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Aalto Doctoral Programme in Science

Application period:

Language of instruction:, eligibility:, field of study:, organising school:, table of contents, choose doctoral studies at the school of science.

The research at our school focuses on advanced energy solutions, condensed matter and materials physics; creation and transformation of technology based business; data science and artificial intelligence; health technology; neuroscience; and software engineering.

Through our internationally-acclaimed high-level research we aim to make a significant impact on society.

Doctoral education pilot

We are hiring 178 new doctoral researchers - get your doctorate from Aalto

Anna Cichonska uses data science to develop better healthcare

Dr. Cichonska has received two awards for her dissertation and now she helps develop preventive medicine using data science

Why can’t AI say ‘I don’t know’?

Overconfident AI systems can be dangerous, so researchers are teaching them humility

Your path to doctoral studies at the School of Science

• Apply for a salaried doctoral researcher position at Aalto. Salaried doctoral researcher positions are advertised at  Aalto University Open positions .
• If you are interested in  full-time studies but there are no open positions at the moment, please directly contact a professor in charge of your intended research field to discuss the possible supervision of doctoral studies. Professors may also have information on other funding possibilities (such as grants), as well as on upcoming positions that are not yet announced.
• If you are employed elsewhere but wish to pursue doctoral studies, that is possible either as a  full-time or part-time student , depending on your situation. In this case, please contact the potential supervising professor directly. Note that to pursue the degree, you need to reside in Finland at least part of the study time.
• In some cases it is also possible to start pursuing doctoral studies without funding (part-time doctoral studies). In this case, please contact the potential supervising professor directly. Note that to pursue the degree, you need to reside in Finland at least part of the study time. Non-Finnish citizens need therefore to take into account  the income requirements of the Finnish Immigration Service. 
• After agreeing with the supervising professor, apply for the study right in our doctoral programme (in addition to a possible working contract at Aalto) - see instructions below. Please note that you are not a doctoral student before you are officially admitted to the doctoral programme, even if you already have a salaried doctoral research position.

Note: Before applying for the salaried positions and/or contacting the potential supervising professor(s), please check below the requirements and qualifications needed for applying for the study right in our doctoral programme.

Discover your research topic and find a supervising professor

Research activities at the departments are arranged under research groups. If your research interest aligns with one of the research groups, it will be easier to find a doctoral study place.

Find research groups under our Department pages Research fields and supervising professors in the School of Science

In addition to the departments' and research groups' pages, you can use Aalto University's research portal for finding the professors who are researching the area in which you want to do your doctoral research. Before applying for doctoral studies you should be aware of the research done and researchers working in the field of your interest.

Aalto University's research portal for finding our researchers and research projects

More information on discovering your research topic and finding a professor

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Basic information on doctoral studies

Objective of studies.

Doctoral students will be equipped with the professional skills and knowledge required for demanding academic research and teaching positions. They will be trained for management, research and development, and other specialist positions of the information society.

The departments, which are in charge of the doctoral programme’s education and research at the School of Science , offer research fields that are based on strong research traditions and research at the highest international level. The School of Science is also very active in various national and international doctoral education networks.

Content of studies and degree structure

Doctoral education at the School of Science is based on vigorous basic research, forming a strong basis for teaching as well as development and innovation activities. The most important part of the education is the research work, which is conducted in a robust and dynamic research environment. The theoretical studies that support the research work are tailored individually to suit the different needs of each doctoral student. The theses of the School of Science are of very high quality and often contain articles published in international peer-review journals. Full-time doctoral students can complete the doctoral degree in four years.

The Doctor of Science (Technology) degree consists of

• an approved doctoral thesis
• research field studies (20-35 ECTS)
• general research studies (5-20 ECTS)

Full-time or part-time studies

All doctoral students are defined as either full-time or part-time students. Doctoral students may not change their study mode by themselves, but it can be changed by application if necessary.

Full-time doctoral students plan their studies with the view to allowing the doctorate to be earned within four years of the right to pursue a doctoral degree being granted. Those applying for a full-time right to pursue a doctoral degree must have funding secured for at least 6 months (e.g. from the employer, or through project funding or a grant). Students employed outside Aalto University must append in their application a certificate issued by the employer proving their possibility to pursue full-time studies (i.e. a minimum of 80% of working hours may be used towards doctoral studies).

Those who do not meet the above criteria for full-time doctoral students are regarded as part-time doctoral students . This category includes, for instance, doctoral students who have a main occupation elsewhere than at the School of Science. Part-time doctoral students plan their studies so as to allow the doctoral degree to be completed in a maximum of eight years.

It is advisable to have a discussion with the part-time students on whether their research is closely connected to their work, and how their employer can support intensive doctoral studies alongside work.

Study language

The language of instruction is, in principle, English, but the doctoral thesis can also be completed in Finnish or Swedish.

The applicants will define in their application in which language they will pursue the degree. The possible languages are Finnish, Swedish, or English. If doctoral students want to write their doctoral thesis in Finnish or in Swedish, the language of the degree will be Finnish or Swedish. If the doctoral thesis is written in English, doctoral students can choose English as the language of the degree that must be approved by the doctoral programme committee. The language of degree can, on reasonable grounds, be changed at a later stage if the language of the doctoral thesis changes.

Funding and fees

The most common ways to fund doctoral studies are

• working in a salaried doctoral researcher position
• personal grant(s) or scholarship(s) from foundations or funding agencies

Most Aalto doctoral students combine different funding sources during their studies. 

How to find and apply for funding for doctoral studies and research? Generally Aalto University does not offer scholarships for doctoral studies. However, there is an on-going scholarship scheme until 2024 for students from African and South American countries: Finland Fellowship .

During the academic year 2024-2025, the Finnish Ministry of Education and Culture is funding 178 new doctoral researcher positions at Aalto University through a doctoral education pilot.

Doctoral education pilot: 178 doctoral researchers' salaried positions

Fees and costs

Aalto University doctoral studies are free of tuition fees. Aalto University does not charge fees for enrollment to the University. Doctoral students are welcome to join the Aalto University Student Union. The membership of the Student Union is subject to an annual fee.

If you need a residence permit for research in Finland, please see more information about income requirement at the Finnish Immigration Services .

International opportunities and Cotutelle

Internationality is an integral part of the school’s doctoral education in both recruiting and educating doctoral students. The School of Science is well connected to a number of top-level international universities and research institutes in its field.

Aalto University encourages its doctoral students to spend at least six months of their study time abroad, as international mobility enhances doctoral students’ career opportunities . Visiting a foreign university or research institute often means sharing knowledge and know-how, creating new ideas, expanding international networks, and developing one’s professional skills.

Cotutelle - joint supervision

The Aalto University encourages doctoral degrees that are jointly supervised with an international partner. These agreements are referred to as Cotutelle Agreements. Arrangements for joint supervision are made in terms of the studies and supervision of a single doctoral student that will be awarded degrees and the associated certificates from both universities.

Cotutelle agreements are part of the university's aim to achieve and maintain high quality of international standards in research and education. International cooperation is an integral part of the doctoral education of Aalto University, and one method for such cooperation is arrangements for the joint supervision of doctoral degrees. A doctoral student may earn a double degree under a joint supervision arrangement between two universities provided that the joint supervision is based on genuine scientific cooperation, bringing added value to the doctoral thesis and enhancing the quality of the research.

Cotutelle agreements should be made at the beginning of the studies but it requires a right to study at the Aalto University before any agreement can be made.

Multidisciplinary opportunities

The doctoral education networks collaborate through seminars, courses, summer schools and events as well as promoting networking, and increasing peer support among doctoral students.

Doctoral education networks

The School of Science operates in the following doctoral education networks:

Brain & Mind CMMP- Network in Condensed Matter and Materials Physics Doctoral Education Network in Systems Analysis, Decision Making and Risk Management ENNUSTE - Doctoral Education Network in Nuclear Science and Technology FDNSS - Finnish Doctoral Education Network in Stochastics and Statistics HICT - Helsinki doctoral education network in information and communications technology Nordic IoT Hub - Nordic collaboration in Industrial IoT

More information

Career opportunities and employability for Aalto doctoral students

Why choose Aalto University?

How to apply?

The Doctoral Programme in Science invites applications continuously (applications will not be processed in July). The more exact application times can be found below.

Before submitting the application, each applicant must contact a supervising professor who is responsible in their intended research field to doctoral studies and the supervision of the studies. Applicants are urged to ensure that their expertise and research interests are commensurate with the research group (and those of the supervising professor of their studies) that they apply to.

Application dates & deadlines

Applies to all applicants, with the exception of applicants for part-time doctoral studies in the research field of Industrial Engineering and Management .

Applicants to the research field of Industrial Engineering and Management

• Applications are invited from full-time applicants to the research field of Industrial Engineering and Management once a month. The application deadlines are identical with those of other research fields in the programme, please see deadlines above.
• Applicants to part-time doctoral studies in the field of Industrial Engineering and Management may apply twice a year.

Application periods 2024: part-time applicants, Industrial Engineering and Management

Processing the applications

Each application is processed in the next possible meeting of the Doctoral Programme Committee when all the required materials have been received. Only applications with all the required materials will be processed. Incomplete applications will be rejected, unless the missing materials are sent by the deadline given. The right to pursue a degree will be valid only after the dean has granted the right and the applicant has accepted the offer of admission. The applicant has two weeks to accept the offer and cannot postpone the start of the right to pursue a degree.*

*Please note:

From 1 August 2016 onwards applicants who have been given an offer of admission may accept only one student place leading to a higher education degree in Finland during one academic term (Universities Act 558/2009). Higher education degrees include bachelor’s, master’s, and doctoral degrees awarded by universities as well as degrees from universities of applied sciences.

The academic terms run from 1 August to 31 December and from 1 January to 31 July. The acceptance of a student place is binding and cannot be cancelled. Even if the accepted applicants postpone the commencement of studies or give up their right to study, they cannot accept another study place leading to a higher education degree starting the same academic term.

Eligibility

The general eligibility criteria for higher education are defined in the Universities Act (558/2009, section 37) and in the Aalto University Student Admissions Criteria for 2023.

Eligible applicants for studies leading to a doctoral degree from the Doctoral Programme in Science will have completed:

• a relevant master’s degree awarded by a university;
• a relevant master’s degree awarded by a university of applied sciences; or
• a relevant study programme abroad which in the awarding country gives eligibility for the corresponding level of higher education.

The university may require a student admitted to study towards an academic or artistic licentiate or doctoral degree to complete supplementary studies in order to acquire the knowledge and skills needed for the study programme.

Policy on the recognition of degrees awarded outside Finland

Applicants holding a degree earned abroad are eligible for doctoral studies provided their degree gives them eligibility for corresponding higher education in the awarding country. As a general rule, the grounds for Aalto’s recognition of degrees earned abroad is that the normative time to attaining them is at least four years, which includes a master’s thesis or the equivalent, and that such studies in the view of the school equip the student with the skills and knowledge needed to pursue doctoral studies at the school. The general policy on the recognition of a European degree as the basis for doctoral degree studies is that it be a higher-education degree combination (3+2 years) earned in accordance with the Bologna Process principles.

Eligibility on the grounds of higher-education degrees with a structure differing from the abovementioned are considered on a case-by-case basis. In such cases, attention will focus particularly on how well the degree has prepared the applicant to pursue doctoral studies.

Policy on the recognition of master’s degrees from Finnish universities of applied sciences

Applicants with a master’s degree in a relevant field earned at a Finnish university of applied sciences are reviewed on a case-by-case basis for their aptitude to pursue doctoral studies. If the school deems the applicant with a relevant master's degree from a university of applied sciences as having the potential to complete the doctoral degree, the applicant will be assigned sufficient supplementary studies to allow him or her to begin the doctoral/licentiate studies. The scope of the supplementary studies may not, however, exceed 60 ECTS credits. If the scope of the supplementary studies exceeds this maximum, the applicant is advised to complete a master's degree at the university level before applying for a right to pursue the doctoral degree.

When assessing the students’ potential for successful doctoral studies and determining their need for supplementary studies, the school will consider the scope of master’s degrees at the student’s university of applied sciences (in Finland, such degrees are of 60–90 cr, less than the 120-credit scope of master’s degrees at Finnish universities such as Aalto).

Applicants with a prior degree earned abroad and corresponding to a relevant Finnish master’s degree from a university of applied sciences are treated equally to those with master’s degree from a Finnish university of applied sciences.

Evaluation criteria

The academic evaluation of the applicant is performed by the supervising professor in charge of the research field sought by the applicant. The Doctoral Programme Committee also evaluates the applicants. In addition, all applicants to the field of industrial engineering and management are evaluated by the Department of Industrial Engineering and Management.

The evaluation of applicants takes into account the following criteria:

Contents of the previous degree(s):

• sufficient basic information concerning the research field applied for; this information is collected from e.g. the major studies or advanced studies that were included in the applicant’s master's degree
• sufficient basic information to support the applicant’s ability to carry out the research work and writing for the doctoral thesis

The School of Science may set prerequisite studies for the applicant to complete by e.g. taking master’s level courses.

Academic performance:

• The applicant received a minimum grade of at least 4 (on a scale of 1–5) for the master's thesis
• an average grade of 3.5 (on a scale of 1–5)  for the master’s degree courses (excluding the thesis), OR
• if the applicant earned his/her master’s degree in accordance with the degree regulations of 1995 or earlier (when Finnish bachelor's and master's degree were not pursued separately), he or she received an average grade of at least 3.0 (scale 1–5) for the major at the master's level.

Exceptions to the grade limits mentioned above may be made only for special reasons set forth in a well-founded written statement by the supervising professor. In such cases, the Doctoral Programme will request a statement from the supervising professor.

Other evaluation criteria:

• the quality of the applicant’s university degree and its status internationally
• the applicant’s potential as a researcher; previous experience in research research-related work experience, conference presentations, journal articles, etc.
• relevance of the research topic: to ensure genuine research interest by the supervising professor and adequate resources to advise the student in the research of the department’s focus area
• the research proposal: the theoretical and practical innovative value of the topic; the feasibility of the research proposal (its quality, planned methods, etc.)
• time management and resources: the research proposal and the time the student has available for the doctoral studies over the next four (4) years
• the supervising resources of the university in the research field
• other grounds for admission presented by the applicant

Applicant evaluations for the research field of industrial engineering and management:

The Department of Industrial Engineering and Management and the supervising professor are responsible for evaluating applicants to the research field of industrial engineering and management. The Doctoral Programme will request an evaluation statement from the department. Preference will be given to applicants who have shown outstanding academic performance and are otherwise strongly qualified for doctoral studies in the department.

Required language proficiency

Successful applicants will have excellent skills in Finnish, Swedish, or English. The applicant chooses the language(s) of instruction that he/she will use for demonstrating proficiency.

Proficiency in a national language of Finland is demonstrated in accordance with the ‘General recommendations for admissions criteria for Finnish universities’.

Proficiency in English may be demonstrated in one of the following ways:

• The applicant has earned a degree taught in Finnish, Swedish or English in a higher education institution in Finland;
• The applicant has earned an English-medium higher education degree in an EU/EEA country, Australia, Canada, New Zealand, South Africa, Switzerland, the United Kingdom or the United States while residing in the respective country;
• The applicant has received his or her primary and secondary education in English in an EU/EEA country, Australia, Canada, New Zealand, South Africa, Switzerland, the United Kingdom or the United States while residing in the respective country;
• The applicant has completed the Aalto Executive Education MBA, EMBA or DBA degree; 
• The applicant has completed CEMS Master in International Management entity; or
• Applicants submit their English-language test results in accordance with the information below.

In points 1–3 of the above list, a minimum of one half of the aforementioned degree must be completed in a country and higher education institution that meets the requirements for exempting the student from taking an English test. The language of the degree must be stated unambiguously in the degree certificate or its appendix, or in the transcript of records or other official document issued by the awarding institution. If the degree was completed in more than one language, the appendix must clearly indicate the amount of studies that were completed in English.

In points 1 – 2 of the above list, a university degree showing language proficiency must be at least three years' lower university degree, at least one year's higher university degree or doctorate. The university must be a recognised part of the country's official national education system. The university must be found on the country's official list of recognised universities with a right to degree-granting or on a list of recognised universities maintained by an international organisation (e.g., UNESCO). 

The university must be recognised in the country of point 1 or 2.

The recognized English language tests and their minimum scores required for admission to doctoral studies are (Aalto University Admissions Criteria 2022):

• IELTS (Academic): 6.5, and 5.5 for Writing;
• IBT (Internet-based Test): 92, and 22 for the Writing section or
• iBT® Special Home Edition: 92 and 22 for the Writing section
• PDT (Paper-Delivered Test): Reading 22, Listening 22, and Writing 24
• C1 Advanced, prev. Cambridge Certificate in Advanced English: A,B or C
• C2 Proficiency, prev. Cambridge Certificate of Proficiency in English: A,B,C or Level C1
• Pearson Test of English Academic (PTE A): 62, and 54 for writing
• When it comes to the IELTS and TOEFL tests, the following online tests are also accepted: TOEFL iBT® Special Home Edition ja IELTS Indicator (Academic).

In addition, at the School of Science, an English language test is not required in doctoral admissions of applicants who have:

• been deemed by their supervising professor as having sufficient proficiency in English to pursue doctoral studies. The supervising professor must submit a written statement on the language skills of the applicant and the statement should be added in the application. If the applicant does not submit the statement together with other application documents the Doctoral Programme will request the statement from the supervising professor.

Submission of English test result:

Only official reports of the language test are acceptable as proof of proficiency.

• For IELTS test, upload a copy of the official test report (as a PDF) to the application system. The test results are verified through the test administrator’s electronic verification service.
• TOEFL test results must be sent to Aalto University by the test administrator directly. Request your official score report to be sent from the test administrator to Aalto University reporting code  7364 . Unofficial score reports sent by applicants will not be accepted. Test scores submitted with the Aalto University reporting code are checked for authenticity in the test administrator’s verification database. The scores are available within 1 to 2 weeks of sending the score report request.
• PTE test scores are sent via the test administrator’s electronic service. Applicants who took the PTE test must log in to their PTE account and send their results in the system to Aalto University. The test administrator notifies by email when the results have been sent to the university.
• For the C1 Advanced or C2 Proficiency language test, upload a PDF copy of the results report to the application system. The test-taker’s ID number (e.g. ABC1234567) and reference number (e.g. 173YU0034522) must be entered in the system. Test takers must be logged in to the language test system to submit their results to Aalto University. The results are verified electronically.

Validity of the language test

The language test result has to be valid at least on the day of the Doctoral Programme Committee meeting where the applicant's application is processed.

More information on the language tests can be found on the pages of the test providers:

• IELTS  (ielts.org)
• TOEFL  (ets.org)
• PTE Academic  (pearsonpte.com)
• C1 Advanced (cambridgeesol.org)
• C2 Proficiency (cambridgeesol.org)

Application procedure

• Read the application instructions carefully and prepare all the required appendices (listed and explained in more detail below). Remember signatures of yourself, your supervising professor and thesis advisor for all necessary documents. By signing these documents, the professor confirms to be your supervising professor.
• Apply on the online application system (Studyinfo.fi, current link below). In the beginning of the application form, please choose the Doctoral Programme in Science as your study programme (" Add study programme"). 
• For choosing the mode of study, see the definition of full-time and part-time doctoral students.
• Language of the degree: Choose English unless you wish to write your doctoral thesis in Finnish or Swedish.
• Fill in the application carefully. The required appendices depend on your choices.
• Attach all the required documents as pdf documents. There are some documents required for every applicant and others required only for those whose Master's degree is from elsewhere than Aalto University. Please see the details below.
• Submit the application by the deadline.
• Send certified hard copies / verified documents of the required degree documents if your M.Sc. degree is from elsewhere than Aalto University or one of its preceders (explained in more detail below). Remember that these are needed before admission.

Required appendices for all applicants

Please submit the following appendices in Studyinfo.fi when using the Electronic application form .

In the application form, please choose Doctoral Programme in Science as a study programme ("Add study programme").

The study plan, research plan, supervision plan and funding plan must all be approved and signed by both the applicant and the supervising professor . Upon his or her signature of the documents, the professor in charge of the research field agrees to act as the supervising professor of the applicant.

After reading the instructions and getting all the documents ready, fill in the application, attach all the required documents (and the additional appendices required for those with master's degree elsewhere than at Aalto University) and send it.

Curriculum vitae (CV)

Include a list of publications and proof of other scientific activity. Template for a researcher's CV .

Credit plan

A preliminary Study plan (credit plan) for the theoretical studies of the degree, 30 ECTS. You and your supervising professor have to sign this document. 

See the Curriculum of the Doctoral Programme in Science for instructions.

Research plan

Research plan with an implementation schedule.

Funding plan

Funding plan is a free format document including the following information:

The source, the amount and the start and end dates of secured funding, More information on funding your doctoral studies (aalto.fi)

Supervision plan

Carefully read the guidelines , which give detailed information about the mutual duties and responsibilities of the supervising professor, thesis advisors and doctoral student, before filling in the responsibilities to the Supervision plan template .

• You can have  1–3 thesis advisor(s). Theses advisors need to have a doctoral degree (remember to check this especially in case of advisors who work outside Aalto University). The supervising professor can be one of the thesis advisors. In case you don't have separate advisor(s), supervising professor will be nominated to both roles.
• You, your supervising professor, (possible co-supervisor) and thesis advisor(s) have to sign this document.

At SCI a deputy supervising professor has to be assigned always. The deputy professor has to be a tenure-track professor of the school.

Identification document

Copy of the identity page of the passport or other official identification that indicates the citizenship of the applicant.

Copy of the degree certificate and the transcript of study records

• Master's degree certificate
• Official transcripts of records of all the courses included in the master’s degree
• All the appendices of the degree documents (typically the Diploma Supplement in European Higher Education Area). 
• Official translations of the degree certificate and the transcript of records, if the originals are not in Finnish, Swedish, or English.
• The (translated) documents should clearly indicate the thesis grade, evaluation and the grading scale used.

Note, if your degree is from Aalto University, you can submit only the official transcript of records. 

Please upload these as scanned copies to the electronic application form in Studyinfo. Depending on the situation and your choices in the form, you may need to upload these documents twice. This is because of the structure of the form.

Please submit also the certified hard copies /verified degree documents according to the instructions described below . Submit the certified copies/verification documents to the doctoral programme before admission. Please note that certified hard copies will not be returned to you. In case your master's degree is from Aalto University (or any of its preceders), or from another University in Finland (degree completed after 2003) and you have a Finnish personal identification code, the certified copies are not required.

Proof of proficiency in Finnish, Swedish or English

In the application form, you choose how you demonstrate the language proficiency. Depending on your master's degree origin, you demonstrate the language proficiency either by your master's degree certificate and transcripts, or by an English-language test. See the details about different options in Language proficiency section above.

Pay attention that the degree language is mentioned in your degree documents (in options 2-3 of demonstrating the language proficiency ). Please contact [email protected] , if you have questions regarding your language proficiency.

Submitting the English-language test result (in option 6)

• A copy of the official IELTS score report (PDF-copy) is uploaded in the application system. The test result will be verified by Aalto University from the test provided.
• PTE scores are submitted through the electronic result service. The applicant need to sign in to his/her own PTE-account and send the test result through the electronic certification service to Aalto University. The test provider will inform by e-mail, when the test score has been submitted to the University.
• A copy of the C1 Advanced or C2 Proficiency language test score report (PDF-copy) is uploaded in the application system. The ID-number (e.g. ABC123456) and the reference number (e.g. 173YU0034522) need to be mentioned on the application form. The applicant also need to sign in to the language test system and share the scores with Aalto University. The scores will be verified electronically.

Additional appendices required for those with master's degree elsewhere than at Aalto University

Applicants with a master’s degree or education earned elsewhere than at Aalto University (or at one of its predecessors) must also provide the following documents:

An abstract of master's thesis in English

Please submit the abstract of your master’s thesis in English, so that we know what your master’s thesis was about.

Documents confirming eligibility or degree language

If needed, submit a document confirming eligibility for doctoral studies in the country that awarded the the degree or gave the education (see section Eligibility) and a certified translation of it, if the original document is not in Finnish, Swedish or English. You can attach the document in Studyinfo or send it via email to [email protected] .

You may also need to submit a certificate from the university proving the degree language , if the information is not available in other official degree documents. In this case, please use the same procedure as described above.

Certified hard copies / verified degree document if the degree is awarded by a higher education institution outside Finland

Please, send the certified hard copies / verified degree documents of the required degree documents including official translations (listed above) also by postal mail to our office (Antti Susiluoto, Doctoral Programme in Science, P O BOX 15500, 00076 AALTO) by the application deadline . Please note that certified hard copies will not be returned to you.

Country specific instructions:

Applicants who have completed their master's degree in: Australia, Bangladesh, Cameroon, Canada, China, Eritrea, Ethiopia, Ghana, India, Indonesia, Iran, Ireland, Kenya, Malaysia, Nepal, New Zealand, Nigeria, Pakistan, South Africa, Sudan, the United Kingdom or the United States:

Please note that the required degree documents including official translations need to be submitted according to the country-specific document requirements . Read the requirements on Country-specific requirements , and send the documents to the doctoral programme as required in the "Country specific requirements". If the documents need to be sent by postal mail, the address is: Antti Susiluoto, Doctoral Programme in Science, P O BOX 15500, 00076 AALTO. If you use courier services, please send the documents to this address: Antti Susiluoto, Doctoral Programme in Science, Maarintie 8, 02150 Espoo, Finland. If the documents can be submitted electronically (they can be verified in an electronic system), send them by e-mail to [email protected] . You can also visit our office at Maarintie 8:

Please DO NOT send the documents to the Admission Services as instructed in the country specific requirements webpage.

Certified hard copies if the degree is awarded by a higher education institution in Finland

• If you have completed a degree in Finland after 1 January 2003 and you have a Finnish personal identification code , Aalto University will verify your degree electronically using a national database and you do not need to send anything by postal mail.
• If your degree was completed before 1 January 2003 , or you do not have a Finnish personal identification code, send certified hard copies of the required degree documents (listed above) to our office by postal mail (Antti Susiluoto, Doctoral Programme in Science, P O BOX 15500, 00076 AALTO).

Certified hard copies and translations - detailed instructions

Copies of degree certificates and a transcript of records must be certified by the awarding university or by a notary public . The copies must be taken from the original, official documents. A multiple-page certified copy must be certified on the front side of every page. Each page must have the certifying official’s original signature, printed name, ink stamp and date . Copies of officially certified copies are not accepted, thecertifying official’s ink stamps and signatures must be original. A note declaring official copy status (such as a “True copy” stamp) is insufficient.

The translation is official if it has been done by the higher education institution that awarded the degree or by a certified translator (authorised translator) . The translations must have the certified translator’s original ink stamp and signature.

The official translations must be either original or certified paper copies of the original documents. Unofficial copies of the translations are insufficient. The official translations must be accompanied by certified paper copies of the original documents in the original language. Translations by themselves are insufficient.

Sending certified copies by mail to Aalto University (guidelines given by the Finnish customs)

• Send the consignment of documents as a letter. Do not send it as a parcel.
• Do not determine a value for the letter, when sending it. Do not indicate even the amount paid for a possible insurance for the consignment.  
• If the country of dispatch requires the sender to determine a value for the consignment of documents, the value is zero (euros or other currency).
• The goods description for the consignment should be, for example, documents .

If you have any questions about admissions and application instructions, you can contact [email protected]

In case of programme-specific questions and inquiries, you may also contact the Learning Services of the Doctoral Programme in Science .

Departments of School of Science

Department of mathematics and systems analysis.

Our main research areas are algebra and discrete mathematics, analysis, applied mathematics and mechanics, stochastics and statistics, and systems analysis and operations research.

Department of Computer Science

cs.aalto.fi

Department of Industrial Engineering and Management

We conduct world-class research and education focusing on the creation and transformation of technology-based business.

Department of Neuroscience and Biomedical Engineering

We study system-level dynamic functions of the human brain, mind and body.

Department of Applied Physics

The Department of Applied Physics pursues vigorous research in physical sciences and creates important industrial applications.

• Published: 19.12.2019
• Updated: 16.8.2024

Doctoral Programmes

Faculty of built environment.

Doctoral Programme in the Built Environment  (DPBEN)

Faculty of Education and Culture

Doctoral Programme of Education and Society  (DPEDU)

Faculty of Engineering and Natural Sciences

Doctoral Programme in Engineering and Natural Sciences  (TLTO)

Doctoral Programme in Engineering Sciences  (TTITO)

Faculty of Information Technology and Communication Sciences

Doctoral Programme of Humans and Technologies  (DPHAT)

Doctoral Programme in Media, Communication and Performing Arts  (DPMCP)

Doctoral Programme in Language Studies  (DPLA)

Doctoral Programme of Computing and Electrical Engineering  (DPCEE)

Faculty of Management and Business

Doctoral Programme in Administrative Sciences, Business Studies and Politics  (DPHKP)

Doctoral Programme in Business and Technology Management  (TOTO)

Faculty of Medicine and Health Technology

Doctoral Programme in Medicine, Biosciences and Biomedical Engineering  (DPMBBE)

Faculty of Social Sciences

Doctoral Programme in Literary Studies  (DPLS)

Doctoral Programme in Health Sciences  (DPHS)

Doctoral Programme in History  (DPHI)

Doctoral Programme in Psychology and Logopedics  (DPPL)

Doctoral Programme in Social Sciences  (DPSS)

Doctoral Programme in Medicine  (DPMD)

Doctoral Programme in Philosophy  (DPPH)

International Doctoral Programme in Epidemiology and Public Health  (IPPE)

Additional information on doctoral studies

Structure and duration of doctoral studies.

In addition to the doctoral dissertation, the requirements for a doctoral degree include other studies, which you should plan to support your doctoral research. The structure of the other studies can be found in the curriculum of your doctoral programme.

For full-time doctoral students, the target time of completing the doctoral degree is four years. Part-time students may take longer to complete their degree.

Doctoral dissertation

To earn a doctoral degree, students must complete a dissertation and defend it in a public examination. Students prepare a dissertation to demonstrate their ability to produce original scientific knowledge in the field of their research. Writing the dissertation requires that the student is capable of conducting independent scientific research.

Tampere University Doctoral School

The Doctoral School supports the development of diverse, multidisciplinary and international expertise among doctoral researchers and works to promote employability of our doctoral graduates.

You will be able to select courses that meet your needs over 50 courses that the Doctoral School offers each year. We give Finnish and English-taught courses both online and in a physical classroom environment.

The Doctoral School hosts regular events for doctoral researchers such as Orientation Day and open lectures. You get to meet other doctoral researchers, network and receive peer support.

Our courses and events provide you with the opportunity to gain experience of multidisciplinary and international teamwork while making effective progress towards your degree.

Get to know the Doctoral School

Doctoral studies can be financed in a variety of ways and admittance to a doctoral programme does not guarantee funding. Students are recommended to contact their supervisor before starting their doctoral studies to discuss their funding options. Funding options for doctoral studies are at least the following:

• Employment at the University (either project funding or a separate doctoral education funding)
• Scholarships and grants
• Student financial aid  (if eligible)
• Adult Education Allowance of the Education Fund  (if eligible) (motion to terminate the allowance was submitted to the parliament on 15 February 2024)
• Doctoral education pilot at Tampere University

The Doctoral School of Industry Innovations

The Doctoral School of Industry Innovations (DSII) offers Doctoral Researchers a unique opportunity to undertake dissertation research, gain a thorough understanding of product development, tackle real-world business challenges and expand their professional networks. Tampere University hires a Doctoral Researcher to complete a four-year, company-sponsored dissertation project under the joint supervision of a university professor and a company representative. 

Read more about DSII

Finland Fellowship

Finland Fellowship is a new funding option awarded by Tampere University as part of the national Finland Scholarship programme. Non-EU/EEA applicants to Doctoral programmes are eligible to apply. The Finland Fellowship contributes to the salary paid Tampere University and includes a 2000 EUR arrival allowance. The Finland Fellowship funding is available from 2022 to 2024. It is funded by the Finnish Ministry of Education and Culture. Positions funded with the Finland Fellowship funding are published as part of open positions at Tampere University.

Read more about working at Tampere Universities

Additional information on applying

Detailed information on applying to a doctoral programme is available in the admission requirements of the programme and our webpage Applying to Doctoral programmes.

Applying to doctoral programmes

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Doctoral Admissions

Doctoral studies in finland.

Begin your doctoral journey in Finland by exploring programs through the  Studyinfo.fi portal, or by contacting universities directly for detailed information on doctoral study and research opportunities. Ensure you're familiar with each university's application timelines, eligibility criteria, and specific requirements.

Find more information on Doctoral admissions on each university’s website . 

Funding and positions

You'll find tips on scholarship opportunities for doctoral research in the section Doctoral Funding . Universities might also offer paid doctoral and post-doctoral positions.

For doctoral and post-doc researcher positions, follow academic recruitment platforms and the universities’ own announcements.

Resources for researchers

• Access resources, advice, and guidelines tailored for early career researchers through the Finnish Union of University Researchers and Teachers (FUURT) .
• Explore the Finnish science and innovation landscape, including policy and ongoing research, at Research.fi .

Academic research positions and jobs

• Jobs in Finland / Academic
• Academicpositions.fi

2 physics positions in Finland

Filtered by, refine your search.

• Research Job 1

Doctoral Researcher in Power Electronics (DSII)

, mathematical programming, and embedded systems. Our vision is to develop software solutions that fully utilize the capability of the power electronic hardware by operating the system close to its physical limits

University Instructor (Software Quality)

of Unit Timo Hämäläinen, timo.hamalainen(at)tuni.fi University Lecturer Terhi Kilamo, terhi.kilamo(at)tuni.fi, +358408490723 Questions regarding the recruitment process : HR Specialist Teuvo Moilanen

Searches related to physics

• postdoctoral
• materials science
• engineering
• atomic physics
• medical physics
• phd physics

Doctoral defence of Ilakya Selvarajan, MSc, 12 Sep 2024: Cell type specific genetic regulatory mechanisms in human coronary artery disease

Body flexibility in middle age linked to survival, doctoral defence of obed asamoah, msc, 5.9.2024: evaluating local perceptions of sustainable utilisation of non-timber forest products and their potential to alleviate poverty in ghana's forest fringe communities, obed asamoah, msc: doctoral defence in forest science, online, opening ceremony of the academic year 2024–2025, kalle karjalainen, msc: doctoral defence in applied physics, kuopio.

Find more news and events

Refine your search

UEF Doctoral School

The University of Eastern Finland's Doctoral School and the associated doctoral programmes are responsible for arranging scientific doctoral studies at our university. Our doctoral programmes offer teaching and supervision for doctoral researchers. The aim is to ensure the high quality of doctoral education and to educate highly skilled researchers and experts.

The director of the doctoral school is Academic Rector Tapio Määttä. Administration of the school is coordinated by Head of Education Kaisa Laitinen, and the development of the doctoral school's activities and teaching programme are coordinated by Senior Lecturer Merja Lyytikäinen (contact information below).

Upcoming public examinations of doctoral dissertations

New in doctoral education

The University of Eastern Finland is involved in 11 doctoral education pilots. New doctoral positions with three-year employment contracts will be available.

Learn more about the doctoral education pilots

Doctoral programmes

Doctoral education in the University of Eastern Finland is arranged in 13 discipline specific or thematic doctoral programmes. Further information about applying to programmes, research areas and doctoral studies can be found on the homepages of doctoral programmes.

Philosophical Faculty

• Doctoral Programme in Educational Studies
• Doctoral Programme in Social and Cultural Encounters
• Welfare, Health and Management (WELMA) Doctoral Programme

Faculty of Science, Forestry and Technology

• Doctoral Programme in Science, Forestry and Technology

Faculty of Health Sciences

• Doctoral Programme in Clinical Research
• Doctoral Programme in Drug Research
• Doctoral Programme in Molecular Medicine
• Doctoral Programme in Health Sciences

Faculty of Social Sciences and Business Studies

• Past, Space and Environment in Society Doctoral Programme
• Doctoral Programme in Business Studies
• Doctoral Programme in Law

Content related to doctoral education

Instructions and forms

Find information for different phases in the doctoral education on Kamu Student handbook.

Doctoral researcher positions

Learn more about salary-paying UEF doctoral researcher positions and shared doctoral researcher positions.

For grant-based researchers

We have gathered information and instructions for grant-based researchers in Kamu Student handbook.

Conferment ceremonies

The Doctoral Conferment Ceremony shows appreciation for persons who have completed a doctoral degree.

Contact information

The UEF Doctoral School coordinates doctoral education at the university and provides transferable skills studies to all of the university's doctoral students. All doctoral students are automatically included in the doctoral school.

Doctoral programmes processes applications and makes proposals for the faculties on the rights to study to be granted. They are responsible for the organisation of subject-related doctoral studies, and for the supervision of doctoral students.

Faculties are responsible for the administration of doctoral studies. Faculties decide on requirements of doctorates, approve the doctoral studies curricula, grant the right to pursue doctoral studies, approve the research topic and research supervisor(s), research and doctoral study plans and any changes made to these. Faculties also appoint the preliminary and final examiners for doctoral dissertations and licentiate theses and the opponents and the chairman of the public examination (the Custos) for doctoral dissertations. Faculties grant the permission for the public examination, approve and grade the licentiate thesis and the doctoral dissertation, and approve completed doctoral degrees, award the degrees and give the degree certificates.

Development of the doctoral school's activities and teaching programme: Senior Lecturer Merja Lyytikäinen .

Administration of the doctoral school: Head of Education Kaisa Laitinen .

Contact information of the directors and coordinator of the doctoral programmes can be found on the homepages of programmes .

Contact person: Amanuensis Kaisu Kortelainen .

E-mail: [email protected]

E-mail: lumetdissertations(at)uef.fi

E-mail: [email protected]

Contact persons: Head of Education Annikki Honkanen and Academic Affairs Coordinator Anne Korhonen .

27 Best universities for Physics in Finland

Updated: February 29, 2024

• Art & Design
• Computer Science
• Engineering
• Environmental Science
• Liberal Arts & Social Sciences
• Mathematics

Below is a list of best universities in Finland ranked based on their research performance in Physics. A graph of 5.14M citations received by 207K academic papers made by 27 universities in Finland was used to calculate publications' ratings, which then were adjusted for release dates and added to final scores.

We don't distinguish between undergraduate and graduate programs nor do we adjust for current majors offered. You can find information about granted degrees on a university page but always double-check with the university website.

1. University of Helsinki

For Physics

2. University of Oulu

3. Aalto University

4. University of Tampere

5. University of Turku

6. University of Jyvaskyla

7. Abo Akademi University

8. University of Eastern Finland

9. Lappeenranta University of Technology

10. University of Vaasa

11. University of Lapland

12. Hanken School of Economics

13. Turku University of Applied Sciences

14. HAAGA-HELIA University of Applied Sciences

15. Kajaani University of Applied Sciences

16. University of the Arts Helsinki

17. Metropolia University of Applied Sciences

18. Seinajoki University of Applied Sciences

19. Laurea University of Applied Sciences

20. Arcada University of Applied Sciences

21. Oulu University of Applied Sciences

22. Jyvaskyla University of Applied Sciences

23. Satakunta University of Applied Sciences

24. Novia University of Applied Sciences

25. Centria University of Applied Sciences

26. Savonia University of Applied Sciences

27. Vaasa University of Applied Sciences

The best cities to study Physics in Finland based on the number of universities and their ranks are Helsinki , Oulu , Espoo , and Tampere .

Physics subfields in Finland

PhD Physics programs in Finland

Particle physics and astrophysical sciences.

University of Helsinki

The Times Higher Education World University Rankings is the only global university performance table to judge research-intensive universities across all of their core missions: teaching, research, knowledge transfer and international outlook.

University of Eastern Finland

Deadline information, best universities with physics in finland.

Bachelor Physics programs in Finland

Master Physics programs in Finland

Most Popular Physics programs in Finland

PhD Physics programs in Finland

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PhD in Finland 2024: Scope, Universities & Scholarships

• German Universities

Updated on 18 July, 2024

Sr. Content editor

In  2024, Finland’s universities welcomed around 53800 students of non-Finnish nationalities, with approximately 80% from outside the EU/EEA area. The country offers high-quality education at all levels of study.

Did you know that most universities in Finland offer PhD programs for free?Not only this, the students also get stipends to cover their living costs. Not only this, the students also get stipends to cover their living costs. 

In this article, we have formulated an ultimate guide to pursuing a PhD in Finland, including the scope of PhD, specializations offered, admission requirements, top universities, career prospects, and much more. for students wanting to study abroad.

Table of Contents

• PhD Opportunities in Finland

What is Scope of PhD in Finland

The licentiate degree, national doctoral program, the standard research phd, phd in finland program length, free phd in finland for international students, engineering, computer science, social sciences, natural sciences, top 5 universities for phd in finland, documents for phd in finland application, cimo fellowships, university of helsinki doctoral program scholarships, edufi fellowships, aalto university school of business doctoral scholarships, career prospects after completing phd in finland, phd opportunities in finland .

The key details of opportunities for PhD in Finland are mentioned in the table below:

• Finland offers a unique and enriching experience for students wanting to study abroad for higher education, particularly a doctorate. The Finnish education system is known for its high-quality education, top universities in Finland for PhD, innovative teaching methods, and research-oriented approach.
• Students are encouraged to take ownership of their research projects, develop critical thinking skills, and contribute to the academic community. Doctoral studies in Finland usually take four years to complete, and students during the program are expected to deliver a doctoral thesis based on their research.
• Studying for a PhD degree gives access to the   finest research facilities and equipment. Finnish universities in   Finland for PhD are well-funded and equipped with modern technology, providing students with the resources to conduct their research effectively. The multicultural environment and welcoming community also make it an ideal place for international students.
• Another interesting aspect of pursuing  a PhD from Finland is that there is no tuition cost involved.

PhD in Finland Structure (The Bologna Process)

The Bologna Process started in 2005 in Finland. It brought structural changes to higher education in Finland. Through this process, changes are made in degree structure and curriculum.

Finnish universities changed to a new system of the number of teaching hours, which were equivalent to one ECTS (European Credit Transfer and Accumulation System) credit. This transition was possible through special projects with special coordination across the universities.

Students aiming for higher education abroad can rely on research universities and universities of applied sciences in Finland. The reforms that came with the Bologna Process gave universities independent legal status and increased autonomy in finances and management. Finland's PhD programs are research-focused, with universities responsible for a significant portion of the country’s research output.

In Finland, there are two degrees available after a master's. Here is a brief discussion of both degrees.

In Finland, the licentiate degree is the initial research degree, offering a smaller thesis than a doctoral dissertation and compulsory classes. This final work of the licentiate degree proves the capacity of independent research, which can be monographic or based on articles.

 After the examination, it should be submitted and published in the university’s database. Two doctoral-level examiners evaluate the thesis within two months, awarding the grades denoting their performance- distinction, pass or fail. 

Since August 2020, licentiate studies require 40 ECTS credits, including discipline-specific and transferable skills studies. The thesis must be submitted for plagiarism analysis before viva vacation.

A doctorate in Finland comprises a dissertation and 40 ECTS credit hours of coursework. Generally, it takes four years to complete this degree. The emphasis is on a research component and engagement in the academic community. Discipline studies encompass compulsory ones, amounting to 30 ECTS credits, and optional transferable skills, totaling 10 ECTS credits.

Every course is different and has different ways of completion, such as lectures, exams, and seminars. It is important to note that the existing curricula are reviewed every three years. The students are also urged to participate in scholarly activities such as international conferences and research visits. 

Types of Finnish Doctorate

A PhD in Finland typically takes 4 years and is offered by universities. Finnish doctoral programs emphasize research excellence and student involvement. Each university has its own specific admission criteria and application timelines that candidates should review.

The two types of Finnish doctorate are as follows:

The National Doctoral Program in Finland includes fully-funded doctoral positions salaried by different entities. The Helsinki Doctoral Educational Pilot is one such initiative where the Ministry of Education and Culture, Finland, funds the positions completely. It offers a 36-month employment to the selected candidate with three intake periods. The selected individuals in this PhD program in Finland require no additional Finland PhD Scholarships to finance their doctoral endeavors. 

In Finland, paying for doctoral studies through grants or self-funding is possible. Self-funding students mostly work on the dissertation part-time while holding another job or doing other tasks.

Ideally, work related to the dissertation topic can be negotiated with the employer. If the work is unrelated, study leave or adult education allowances might be options. 

Usually, it takes about four years to complete a PhD if the candidate works full-time, but if they work part-time, the time can extend beyond this. Despite the scholarships, the doctoral researchers are accorded several facilities funded by the universities, such as electronic services, library services, concessional diets, and UniSport services.

The regular process for obtaining a PhD in Finland lasts four academic years for a full-time candidate. The first part of the curriculum, often completed within the first one and a half to two years, comprises major subjects, general methods, and philosophy of the discipline. During the program, the students are exposed to teaching and key competencies required in a postdoctoral discipline. Annual registration requires filing several achievements and outlining future aims and objectives for research projects with one's supervisor.

Many PhD programs are fully funded in Finland, and the candidates are expected to cover only their living expenses. Adequate funding sources are universities' departments that also provide information on paid doctoral positions and scholarships.

In other words, they offer starting money for up to one year of doctoral study while the university's departments administer and apply for these fellowships on your behalf through EDUFI fellowships.

Specializations Offered in PhD in Finland

There is a wide range of specializations in various fields of study PhD in Finland. Some of the popular disciplines include:

Pursuing a PhD in Engineering in Finland will let you learn with some of the leading engineers in the world. Universities in Finland for PhD offer specializations in fields such as Civil Engineering, Mechanical Engineering, and Electrical Engineering.

A PhD in Business in Finland will provide you with the opportunity to join forces with leading academics in the field. Finnish universities offer specializations in fields such as Marketing, Management, and Finance.

Finland is home to the leading computer science programs in the world. Pursuing a PhD in Computer Science in Finland allows you to collaborate with professionals in the field and contribute to groundbreaking research.

Universities in Finland for PhD   offer specializations in fields such as Educational Psychology, Educational Leadership, and Curriculum Studies. Pursuing a PhD in Education in Finland offers you the prospect of working with top academics in the field and contributing to the education system's development.

Finland has the top Social Science programs in the world. Getting a PhD in Social Sciences in Finland allows you to partner with specialists in the field and conduct unexplored research.

PhD programs in Finland in Natural Sciences focus on chemistry, physics, and mathematics research. Students in these programs undertake independent research, attend seminars and workshops, and publish their research in academic journals.

Finland has several top-ranked universities offering PhD programs. Here are the top 5 universities for PhD in Finland based on the QS World University Rankings, their specializations.

Source: QS World University Rankings 2025

PhD in Finland for International Students: Admission Requirements for 2024 

The admission requirements for a PhD in Finland vary depending on the university and the field of study.

General Requirements for PhD in Finland:

• A master's degree or equivalent in a related field of study
• Proof of English language proficiency (TOEFL iBT, 92 with minimum score of 22 in each section, and for IELTS, overall score 6.5 and minimum 6.0 in writing section), or equivalent)
• Letters of recommendation from academic referees
• A statement of purpose outlining your academic goals and research interests
• Application form (hardcopy or softcopy as per the requirement of the university/ college)
• Transcripts of records
• Upper secondary-level educational documents
• Degree certificates/ officially certified copies awarded by the main university
• Score reports of IELTS/ TOEFL/ PTE/ Cambridge Proficiency
• Score reports of SAT/ GRE/ GMAT
• Letters of Recommendation
• Statement of Purpose
• Other documents such as portfolio/ sample work, etc.
• Proof of finances
• Medical tests

The application process for PhD programs in Finland involves the following steps:

• Find the universities and PhD programs in Finland   you are interested in.
• Check the admission requirements and application deadlines for each program.
• Prepare your application materials, including transcripts, letters of recommendation, and a research proposal.
• Submit your application materials online or by mail.
• Wait for the university to inform you of their decision.

The application deadline varies depending on the university and the field of study PhD in Finland.

Scholarships for PhD in Finland

There are various scholarships available for PhD in Finland for Indian students   and international students pursuing a PhD in Finland. Scholarships offer financial assistance to students and can help cover tuition fees, living expenses, and research costs. Here are the top scholarships for PhD in Finland:

The CIMO Fellowships are awarded by the Finnish National Agency for Education to pursue a doctoral degree in Finland. The scholarship covers the living expenses and provides a monthly allowance of €900 to €1200.

 To be eligible for the CIMO Fellowships, students must submit a complete CV, a motivation letter, and a short research plan (between 2 and 5 pages). They will also have to send out two printed and signed copies of the application form with the required attachments.

The University of Helsinki offers several doctoral program scholarships to both domestic and PhD in Finland for Indian students and international students. As part of the national Finland Scholarship program, the University of Helsinki awards Finland Scholarships that cover 100% of tuition fee and also includes a €5000 relocation grant. Students must have an acceptance letter from the University of Helsinki to apply.

The EDUFI Fellowships are awarded by the Finnish National Agency for Education to pursue doctoral studies or research in Finland. The scholarship covers living expenses, travel costs, and insurance and provides a monthly allowance of €19,00 per month. To be eligible for the EDUFI Fellowships, students must have a Master’s degree, be proficient in English, and have a research proposal that aligns with the research interests of a Finnish university.

The Aalto University School of Business offers several doctoral scholarships to highly qualified international students. The scholarship is awarded as a tuition fee waiver. 

In the first two years, students will receive around €25,000 per year after taxes. This money comes from a mix of salary and grants from foundations. Starting from the third year, students are responsible for finding their funding. 

They can do this by getting paid jobs as researchers or by applying for grants from foundations. The school may also provide fully paid positions to top applicants. Usually, students find funding for the third and fourth years of their studies.

Also, PhD in Finland for Indian students must have a research proposal and an acceptance letter from the Aalto University School of Business to apply.

Completing a PhD in Finland can open up various career opportunities, both in academia and industry. Here are the top career prospects for PhD graduates in Finland:

Source: Payscale(as of July 2024)

Conclusion 

Pursuing a PhD in Finland can be a rewarding experience academically and professionally. The country’s high-quality education system, supportive academic environment, and ample research opportunities make it an ideal destination for international students seeking to advance their education and career prospects. If you are considering a PhD in Finland, explore the universities in Finland for PhD requirements, scholarships, and funding opportunities available. With the right preparation and research, you can unlatch the doors to a successful academic and professional future in the ‘Land of a Thousand Lakes.’

Can Indian students apply for PhD programs in Finland?

Yes, Indian students can apply for PhD programs in Finland. However, they must meet the same academic and language proficiency requirements as other international students.

Which universities in Finland offer PhD programs?

Many universities in Finland offer PhD programs across various fields, including the University of Helsinki, Aalto University, University of Turku, and Tampere University, among others.

Is it difficult to secure funding for a PhD in Finland?

While funding opportunities for PhD students in Finland can be competitive, many scholarships and grants are available to help support international students pursuing a PhD in Finland. Researching and applying for funding opportunities early is important to increase your chances.

Neha Uppal is a passionate content creator and editor. She carries 7.5+ years of experience working with leading edutech companies where she worked as a Faculty, Community Manager, and Content Marketeer. At upGrad, she is helping out people keep informed about the scopes and opportunities of studying abroad via informational articles/blogs.

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[Updated 3 days ago] PhD Scholarships for International students in Finland are below:

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Momeni Iranian Financial Assistance Scholarships, 2024 is a Partial Funding international scholarship offered by the Momeni Foundation for international students. Students eligible for this scholarship are: Open to applicants of Iranian descent

This scholarship can be taken for pursuing in All subjects offered by the university . 30 Jun is the deadline to send applications for Momeni Iranian Financial Assistance Scholarships, 2024. Any institution across the world. You may apply on Momeni Iranian Financial Assistance Scholarships, 2024 application form .

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Boehringer Ingelheim Fonds MD Fellowships 2024 is a Partial Funding international scholarship offered by the Boehringer Ingelheim Fonds (BIF) for international students. Students eligible for this scholarship are: Open to Germany nationals

This scholarship can be taken for pursuing in Biomedicine. Deadline varies is the deadline to send applications for Boehringer Ingelheim Fonds MD Fellowships 2024. Renowned research laboratories all over the World except their home institution and city.. You may apply on Boehringer Ingelheim Fonds MD Fellowships 2024 application form .

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Crivelli Europe Scholarships by UniCredit Foundation 2024 is a Partial Funding international scholarship offered by the UniCredit Foundation for international students. Students eligible for this scholarship are: Open to nationals of all countries where UniCredit is present

This scholarship can be taken for pursuing in Economics, Banking or Finance. 15 Nov is the deadline to send applications for Crivelli Europe Scholarships by UniCredit Foundation 2024. Anywhere across the globe . You may apply on Crivelli Europe Scholarships by UniCredit Foundation 2024 application form .

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Boehringer Ingelheim Fonds (BIF) PhD Fellowships 2024 is a Partial Funding international scholarship offered by the Boehringer Ingelheim Fonds (BIF) for international students. Students eligible for this scholarship are: Open to all nationals

This scholarship can be taken for pursuing in Biomedical research. 01 Oct is the deadline to send applications for Boehringer Ingelheim Fonds (BIF) PhD Fellowships 2024. Any Internationally leading laboratory. You may apply on Boehringer Ingelheim Fonds (BIF) PhD Fellowships 2024 application form .

John Monash Scholarships 2024 is a Partial Funding international scholarship offered by the John Monash foundation for international students. Students eligible for this scholarship are: Open to Australian nationals

This scholarship can be taken for pursuing in All subjects offered by the universities. 01 Jul is the deadline to send applications for John Monash Scholarships 2024. Universities around the world. You may apply on John Monash Scholarships 2024 application form .

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Dissertation Fieldwork Grants 2024 is a Partial Funding international scholarship offered by the Wenner-Gren Foundation for international students. Students eligible for this scholarship are: Open to all nationals

This scholarship can be taken for pursuing in Anthropology. 01 Nov is the deadline to send applications for Dissertation Fieldwork Grants 2024. Any research institution around the World. You may apply on Dissertation Fieldwork Grants 2024 application form .

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Sanders Prize in the History of Early Modern Philosophy 2024 is a Partial Funding international scholarship offered by the Marc Sanders Foundation for international students. Students eligible for this scholarship are: Open to all nationalities

This scholarship can be taken for pursuing in History of Early Modern Philosophy. 01 Oct is the deadline to send applications for Sanders Prize in the History of Early Modern Philosophy 2024. Any institutions across the world. You may apply on Sanders Prize in the History of Early Modern Philosophy 2024 application form .

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Horowitz Foundation Grants 2024 is a Partial Funding international scholarship offered by the Horowitz Foundation for Social Policy for international students. Students eligible for this scholarship are: Open to all nationals

This scholarship can be taken for pursuing in Social Policy. 01 Dec is the deadline to send applications for Horowitz Foundation Grants 2024. Institutions/Universities across the World. You may apply on Horowitz Foundation Grants 2024 application form .

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CSIRO Alumni Scholarship In Physics 2025 is a Partial Funding international scholarship offered by the The Commonwealth Scientific and Industrial Research Organisation (CSIRO) for international students. Students eligible for this scholarship are: Open to all nationalities

This scholarship can be taken for pursuing in Physics and Mathematics. Deadline varies is the deadline to send applications for CSIRO Alumni Scholarship In Physics 2025. Any overseas or interstate institution, such as a university or research establishment of international standing... You may apply on CSIRO Alumni Scholarship In Physics 2025 application form .

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EDUFI Doctoral Fellowships in Finland 2024 is a Partial Funding international scholarship offered by the Finnish National Board of Education for international students. Students eligible for this scholarship are: Open to all nationals except Finland

This scholarship can be taken for pursuing in All courses offered by the universities. Deadline varies is the deadline to send applications for EDUFI Doctoral Fellowships in Finland 2024. Accredited Universities of Finland. You may apply on EDUFI Doctoral Fellowships in Finland 2024 application form .

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Scholarships and Fellowships

Physics scholarships and fellowships.

Current WSU students interested in any Liberal Arts and Sciences scholarship, including physics, must submit an application online at ScholarshipUniverse .

Funding for Undergraduate Students

The Physics department awards the following scholarships:

• Douglas A. Knight Memorial Scholarship
• Jean and Henry Unruh, Jr. Scholarship
• Loper Family Scholarship/Fellowship
• Nelson S. Ladd Physics Scholarship
• Timothy T. Scrivner & Jeanne E. Scrivner Endowed Scholarship

Each award has individual guidelines .

The deadline for scholarship applications is April 1, 2024 for scholarships starting the following academic year. Every physics student should apply .

Math minors and double majors

If you're majoring in physics and minoring or majoring in math, you may qualify for awards specific to mathematics students.

View more information on Mathematics Scholarships

For questions please contact us.

Physics Scholarship Coordinator

Dr. Terrance Figy [email protected] 316-978-5565

LAS Scholarship Coordinator

Debbie Neil 316-978-6656

2022-2023 Awardees

Tonya Keiffer, Tyler Zeller, Krystal Groshans, Octavia Pacheco Vazquez, Dustin Burgardt, Caleb Buhler, Shanli Dace, Dion Samual

2021-2022 Awardees

Jaden Nola, Richard Whitehill, Tonya Kieffer, Ayshea Banes, Tyler Zeller, Krystal Groshans, Octavia Pacheo Vazquez

2020-2021 Awardees

Octavio Pacheco Vazquez, Ayshea Banes, Tyler Nolan, Christopher Wright, Richard Whitehill, Elton Bowman, Koby Bradshaw, Alexandra Olmstead

2019-2020 Awardees

Ryan Pastor, Rebecka Brown, Christopher Wright, Jerrod Horsch 

Funding for graduate students

Hall-schneider family physics fellowship, about evelyn hall.

Evelyn Hall finished her BA in physics at the University of Wichita in 1962 and continued towards a master’s degree in physics, ultimately completing an MS in engineering mechanics at WSU in 1974. She worked in aeronautical engineering on a joint WSU/KU program for four semester working full time at both Boeing and Cessna Aircraft. Evelyn spent nine years with BDM Corporation before returning to Cessna Aircraft and retiring in 2004. Her husband, Charles Schneider, had a 35-year career in engineering and program management before retiring from Boeing in 1993.

Admissions to doctoral studies

The Doctoral Programme has five application periods for doctoral study rights each year – two in the spring, two in the fall and one in the summer (only for applicants who have completed their master's degree at the University of Helsinki). 

2024-2025 the application periods are:

• 4–17 September 2024
• 6–19 November 2024
• 8–21 January 2025
• 2–15 April 2025
• 21–31 July 2025 (only graduates of University of Helsinki)

Please note that the application closes at  3 PM local time  on the last day of the application round.

A doctoral study right can only be gained through the admissions process. Applying to the programme outside the set admission periods is not possible.

In addition to the  university's general requirements for doctoral applicants on eligibility and language proficiency , the doctoral programme requires the following conditions are met:

• Applications must meet the minimum requirements set for  supervisory arrangements  (see selection criteria). The supervisors and the coordinating academic named in the application must have agreed to the task.
• Your previous degree must be  relevant  to the planned research topic and discipline. A degree is regarded as relevant if it includes sufficient studies in a discipline which, given the topic of the proposed doctoral dissertation, can be regarded as a suitable basis for doctoral studies.
• All the studies required for the degree you apply with  completed, graded and registered  by the end of the relevant application period. No exceptions are made to this rule. Applicants who are granted a study right must be able to present a certified copy of their official degree diploma before accepting the offered study place.

Only applications meeting the formal criteria for eligibility continue to scientific evaluation in the doctoral programmes.

The target degree available within the programme is Doctor of Philosophy.

The study right will be granted in Faculty of Science.

Please note that your supervisory arrangements must match your chosen target degree and home faculty. The coordinating academic must be in a permanent or long-term employment  to the faculty  you're applying to.

Availability of high-quality supervision is a central part of the selection criteria. To get started, please see the  contact information . You can also have a look at  the list of our supervisors .

The programme requires that the supervision arrangements presented in the application meet the following requirements:

• You must have  at least one   supervisor  who has completed a doctoral degree, and a  coordinating academic  (professor, associate professor or docent employed by the faculty). 
• The coordinating academic must be in a permanent or long-term employment at the  faculty  you're applying to.
• You must attach  a signed letter of commitment (pdf)  from the supervisor(s) and the coordinating academic mentioned in the application. 

If no one has agreed to supervise you, you are unfortunately not eligible to apply.

Thesis committee must be formed in 6 months after the study right has begun.

Please note that the doctoral programme's decision-making is  not  bound by the preliminary agreements to supervise given by the potential supervisors. The evaluation of the applications is based on their overall quality, and available supervision resources alone do not guarantee acceptance.

The following are emphasized in the assessment of the quality of the research plan:

• Feasibility
• Scientific significance
• Suitability to the programme's research profile

When assessing the provisional timetables presented in the applications, special attention is paid to the fact that a full-time doctoral student should aim to complete the dissertation and related studies in approximately four years. Supervisors are expected to support this goal.

The applicant’s potential and motivation will be assessed on the basis of the quality and feasibility of the research proposal as well as previous academic performance and research experience. The ability to complete the studies in the target duration will be judged on the study plan, research proposal and funding plan. 

Please notice that the right to pursue a doctoral degree at the University of Helsinki does not include funding. In the funding plan, write clearly how you plan to fund your research. If you plan to fund your research yourself (part-time doctoral studies), please make sure that the timetable and estimated year graduation take this into account. Read more about funding doctoral studies on  university's web pages .

The following are emphasized when assessing the quality and suitability of previous studies:

• Suitability of the previous degree as a basis for the planned dissertation project
• Previous study performance

When assessing the study plan presented in the application, the following things are considered:

• Appropriateness for the planned dissertation project

Before drawing up your own preliminary study plan, please acquaint yourself with the doctoral programme's degree requirements. The study plan presented in the application is preliminary, and need not list specific courses. The important thing is that you have given thought on what kind of studies would best support your thesis work and drawn up a preliminary timetable for completing these studies.

Acquainted with the selection criteria and all set to apply? Great! Now go back to the  university's general instructions for doctoral applicants , where you will find all the information you need to prepare and submit your application and the needed enclosures. Good luck!

Decisions on admissions for doctoral studies in the programme are made based on the university’s general criteria for doctoral admissions as well as the programme-specific complementary selection criteria, presented on this page.

The final decision on admission is made by the faculty awarding the applicant’s target degree, based on a proposal from the steering group of the doctoral programme.

A  timetable for decisions  is available in the university's general instructions for doctoral applicants.

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The American Astronomical Society (AAS) , established in 1899 and based in Washington, DC, is the major organization of professional astronomers in North America. Its membership of about 7,000 individuals also includes physicists, mathematicians, geologists, engineers, and others whose research and educational interests lie within the broad spectrum of subjects comprising contemporary astronomy. The mission of the AAS is to enhance and share humanity's scientific understanding of the universe.

The Institute of Physics (IOP) is a leading scientific society promoting physics and bringing physicists together for the benefit of all. It has a worldwide membership of around 50 000 comprising physicists from all sectors, as well as those with an interest in physics. It works to advance physics research, application and education; and engages with policy makers and the public to develop awareness and understanding of physics. Its publishing company, IOP Publishing, is a world leader in professional scientific communications.

A publishing partnership

First Very Long Baseline Interferometry Detections at 870 μ m

Alexander W. Raymond 1,2,3 , Sheperd S. Doeleman 1,2,151 , Keiichi Asada 4 , Lindy Blackburn 1,2 , Geoffrey C. Bower 5,6 , Michael Bremer 7 , Dominique Broguiere 7 , Ming-Tang Chen 4 , Geoffrey B. Crew 8 , Sven Dornbusch 9 , Vincent L. Fish 8 , Roberto García 7 , Olivier Gentaz 7 , Ciriaco Goddi 10,11 , Chih-Chiang Han 4 , Michael H. Hecht 8 , Yau-De Huang 4 , Michael Janssen 18,9 , Garrett K. Keating 2 , Jun Yi Koay 4 , Thomas P. Krichbaum 9 , Wen-Ping Lo 4,12 , Satoki Matsushita 4 , Lynn D. Matthews 8 , James M. Moran 1,2 , Timothy J. Norton 2 , Nimesh Patel 2 , Dominic W. Pesce 1,2 , Venkatessh Ramakrishnan 13,14,15 , Helge Rottmann 9 , Alan L. Roy 9 , Salvador Sánchez 16 , Remo P. J. Tilanus 17 , Michael Titus 8 , Pablo Torne 9,16 , Jan Wagner 9 , Jonathan Weintroub 1,2 , Maciek Wielgus 9 , André Young 18 , Kazunori Akiyama 1,8,19 , Ezequiel Albentosa-Ruíz 20 , Antxon Alberdi 21 , Walter Alef 9 , Juan Carlos Algaba 22 , Richard Anantua 1,2,23 , Rebecca Azulay 9,20,24 , Uwe Bach 9 , Anne-Kathrin Baczko 9,25 , David Ball 17 , Mislav Balokovic 26 , Bidisha Bandyopadhyay 13 , John Barrett 8 , Michi Bauböck 27 , Bradford A. Benson 28,29 , Dan Bintley 30,31 , Raymond Blundell 2 , Katherine L. Bouman 32 , Hope Boyce 33,34 , Roger Brissenden 1,2 , Silke Britzen 9 , Avery E. Broderick 35,36,37 , Thomas Bronzwaer 18 , Sandra Bustamante 38 , John E. Carlstrom 29,39,40,41 , Andrew Chael 42 , Chi-kwan Chan 17,43,44 , Dominic O. Chang 1,2 , Koushik Chatterjee 1,2 , Shami Chatterjee 45 , Yongjun Chen (陈永军) 46,47 , Xiaopeng Cheng 48 , Ilje Cho 21,48,49 , Pierre Christian 50 , Nicholas S. Conroy 2,51 , John E. Conway 25 , Thomas M. Crawford 29,39 , Alejandro Cruz-Osorio 52,53 , Yuzhu Cui (崔玉竹) 54,55 , Rohan Dahale 21 , Jordy Davelaar 18,56,57 , Mariafelicia De Laurentis 58,59 , Roger Deane 60,61,62 , Jessica Dempsey 30,31,63 , Gregory Desvignes 9,64 , Jason Dexter 65 , Vedant Dhruv 27 , Indu K. Dihingia 55 , Sergio A. Dzib 9,7 , Ralph P. Eatough 9,66 , Razieh Emami 2 , Heino Falcke 18 , Joseph Farah 67,68 , Edward Fomalont 69 , Anne-Laure Fontana 7 , H. Alyson Ford 17 , Marianna Foschi 21 , Raquel Fraga-Encinas 18 , William T. Freeman 70,71 , Per Friberg 30,31 , Christian M. Fromm 9,53,72 , Antonio Fuentes 21 , Peter Galison 1,73,74 , Charles F. Gammie 27,51,75 , Boris Georgiev 17 , Roman Gold 76 , Arturo I. Gómez-Ruiz 77,78 , José L. Gómez 21 , Minfeng Gu (顾敏峰) 46,79 , Mark Gurwell 2 , Kazuhiro Hada 80,81 , Daryl Haggard 33,34 , Ronald Hesper 82 , Dirk Heumann 17 , Luis C. Ho (何子山) 83,84 , Paul Ho 4,30,31 , Mareki Honma 80,81,85 , Chih-Wei L. Huang 4 , Lei Huang (黄磊) 46,79 , David H. Hughes 77 , Shiro Ikeda 19,86,87,88 , C. M. Violette Impellizzeri 69,89 , Makoto Inoue 4 , Sara Issaoun 2,150 , David J. James 90,91 , Buell T. Jannuzi 17 , Britton Jeter 4 , Wu Jiang (江悟) 46 , Alejandra Jiménez-Rosales 18 , Michael D. Johnson 1,2 , Svetlana Jorstad 92 , Adam C. Jones 29 , Abhishek V. Joshi 27 , Taehyun Jung 48,93 , Ramesh Karuppusamy 9 , Tomohisa Kawashima 94 , Mark Kettenis 95 , Dong-Jin Kim 8 , Jae-Young Kim 9,96 , Jongsoo Kim 48 , Junhan Kim 97 , Motoki Kino 19,98 , Prashant Kocherlakota 53 , Yutaro Kofuji 80,85 , Patrick M. Koch 4 , Shoko Koyama 4,99 , Carsten Kramer 7 , Joana A. Kramer 9 , Michael Kramer 9 , Derek Kubo 5 , Cheng-Yu Kuo 4,100 , Noemi La Bella 18 , Sang-Sung Lee 48 , Aviad Levis 32 , Zhiyuan Li (李志远) 101,102 , Rocco Lico 21,103 , Greg Lindahl 2 , Michael Lindqvist 25 , Mikhail Lisakov 9 , Jun Liu (刘俊) 9 , Kuo Liu 9 , Elisabetta Liuzzo 104 , Andrei P. Lobanov 9 , Laurent Loinard 105 , Colin J. Lonsdale 8 , Amy E. Lowitz 17 , Ru-Sen Lu (路如森) 9,46,47 , Nicholas R. MacDonald 9 , Sylvain Mahieu 7 , Doris Maier 7 , Jirong Mao (毛基荣) 106,107,108 , Nicola Marchili 9,104 , Sera Markoff 109,110 , Daniel P. Marrone 17 , Alan P. Marscher 92 , Iván Martí-Vidal 20,24 , Lia Medeiros 111,150 , Karl M. Menten 9 , Izumi Mizuno 30,31 , Yosuke Mizuno 53,55,112 , Joshua Montgomery 29,34 , Kotaro Moriyama 53,80 , Monika Moscibrodzka 18 , Wanga Mulaudzi 109 , Cornelia Müller 9,18 , Hendrik Müller 9 , Alejandro Mus 20,24 , Gibwa Musoke 18,109 , Ioannis Myserlis 16 , Hiroshi Nagai 19,81 , Neil M. Nagar 13 , Masanori Nakamura 4,113 , Gopal Narayanan 38 , Iniyan Natarajan 1,2 , Antonios Nathanail 53,114 , Santiago Navarro Fuentes 16 , Joey Neilsen 115 , Chunchong Ni 35,36,37 , Michael A. Nowak 116 , Junghwan Oh 95 , Hiroki Okino 80,85 , Héctor Raúl Olivares Sánchez 117 , Tomoaki Oyama 80 , Feryal Özel 118 , Daniel C. M. Palumbo 1,2 , Georgios Filippos Paraschos 9 , Jongho Park 119 , Harriet Parsons 30,31 , Ue-Li Pen 4,35,120,121,122 , Vincent Piétu 7 , Aleksandar PopStefanija 38 , Oliver Porth 53,109 , Ben Prather 27 , Giacomo Principe 103,123,124 , Dimitrios Psaltis 118 , Hung-Yi Pu 4,125,126 , Philippe A. Raffin 4 , Ramprasad Rao 2 , Mark G. Rawlings 30,31,127 , Angelo Ricarte 1,2 , Bart Ripperda 35,120,121,128 , Freek Roelofs 1,2,18 , Cristina Romero-Cañizales 4 , Eduardo Ros 9 , Arash Roshanineshat 17 , Ignacio Ruiz 16 , Chet Ruszczyk 8 , Kazi L. J. Rygl 104 , David Sánchez-Argüelles 77,78 , Miguel Sánchez-Portal 16 , Mahito Sasada 80,129,130 , Kaushik Satapathy 17 , Tuomas Savolainen 9,15,131 , F. Peter Schloerb 38 , Jonathan Schonfeld 2 , Karl-Friedrich Schuster 7 , Lijing Shao 9,84 , Zhiqiang Shen (沈志强) 46,47 , Des Small 95 , Bong Won Sohn 48,49,93 , Jason SooHoo 8 , León David Sosapanta Salas 109 , Kamal Souccar 38 , Joshua S. Stanway 132 , He Sun (孙赫) 133,134 , Fumie Tazaki 135 , Alexandra J. Tetarenko 136 , Paul Tiede 1,2 , Kenji Toma 137,138 , Teresa Toscano 21 , Efthalia Traianou 9,21 , Tyler Trent 17 , Sascha Trippe 139 , Matthew Turk 51 , Ilse van Bemmel 95 , Huib Jan van Langevelde 89,95,140 , Daniel R. van Rossum 18 , Jesse Vos 18 , Derek Ward-Thompson 132 , John Wardle 141 , Jasmin E. Washington 17 , Robert Wharton 9 , Kaj Wiik 142 , Gunther Witzel 9 , Michael F. Wondrak 18,143 , George N. Wong 42,144 , Qingwen Wu (吴庆文) 145 , Nitika Yadlapalli 32 , Paul Yamaguchi 2 , Aristomenis Yfantis 18 , Doosoo Yoon 109 , Ziri Younsi 53,146 , Wei Yu (于威) 2 , Feng Yuan (袁峰) 147 , Ye-Fei Yuan (袁业飞) 148 , J. Anton Zensus 9 , Shuo Zhang 149 , Guang-Yao Zhao 9,21 , and Shan-Shan Zhao (赵杉杉) 46

Published 2024 August 27 • © 2024. The Author(s). Published by the American Astronomical Society. The Astronomical Journal , Volume 168 , Number 3 Citation Alexander W. Raymond et al 2024 AJ 168 130 DOI 10.3847/1538-3881/ad5bdb

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1 Black Hole Initiative at Harvard University, 20 Garden Street, Cambridge, MA 02138, USA; [email protected]

2 Center for Astrophysics ∣ Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA

3 Current address is Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

4 Institute of Astronomy and Astrophysics, Academia Sinica, 11F of Astronomy-Mathematics Building, AS/NTU No. 1, Sec. 4, Roosevelt Road, Taipei 106216, Taiwan, R.O.C.

5 Institute of Astronomy and Astrophysics, Academia Sinica, 645 North A'ohoku Place, Hilo, HI 96720, USA

6 Department of Physics and Astronomy, University of Hawaii at Manoa, 2505 Correa Road, Honolulu, HI 96822, USA

7 Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, F-38406 Saint Martin d'Hères, France

8 Massachusetts Institute of Technology Haystack Observatory, 99 Millstone Road, Westford, MA 01886, USA

9 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany

10 Dipartimento di Fisica, Universitá degli Studi di Cagliari, SP Monserrato-Sestu km 0.7, I-09042 Monserrato, Italy

11 INAF–Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047, Selargius, CA, Italy

12 Department of Physics, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 106216, Taiwan, R.O.C.

13 Astronomy Department, Universidad de Concepción, Casilla 160-C, Concepción, Chile

14 Finnish Centre for Astronomy with ESO, FI-20014 University of Turku, Finland

15 Aalto University Metsähovi Radio Observatory, Metsähovintie 114, FI-02540 Kylmälä, Finland

16 Institut de Radioastronomie Millimétrique (IRAM), Avenida Divina Pastora 7, Local 20, E-18012, Granada, Spain

17 Steward Observatory and Department of Astronomy, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA

18 Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands

19 National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

20 Departament d'Astronomia i Astrofísica, Universitat de València, C. Dr. Moliner 50, E-46100 Burjassot, València, Spain

21 Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, E-18008 Granada, Spain

22 Department of Physics, Faculty of Science, Universiti Malaya, 50603 Kuala Lumpur, Malaysia

23 Department of Physics & Astronomy, The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, USA

24 Observatori Astronòmic, Universitat de València, C. Catedrático José Beltrán 2, E-46980 Paterna, València, Spain

25 Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, SE-43992 Onsala, Sweden

26 Yale Center for Astronomy & Astrophysics, Yale University, 52 Hillhouse Avenue, New Haven, CT 06511, USA

27 Department of Physics, University of Illinois, 1110 West Green Street, Urbana, IL 61801, USA

28 Fermi National Accelerator Laboratory, MS209, P.O. Box 500, Batavia, IL 60510, USA

29 Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA

30 East Asian Observatory, 660 North A'ohoku Place, Hilo, HI 96720, USA

31 James Clerk Maxwell Telescope (JCMT), 660 North A'ohoku Place, Hilo, HI 96720, USA

32 California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA

33 Department of Physics, McGill University, 3600 rue University, Montréal, QC H3A 2T8, Canada

34 Trottier Space Institute at McGill, 3550 rue University, Montréal, QC H3A 2A7, Canada

35 Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo, ON N2L 2Y5, Canada

36 Department of Physics and Astronomy, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada

37 Waterloo Centre for Astrophysics, University of Waterloo, Waterloo, ON N2L 3G1, Canada

38 Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA

39 Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA

40 Department of Physics, University of Chicago, 5720 South Ellis Avenue, Chicago, IL 60637, USA

41 Enrico Fermi Institute, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA

42 Princeton Gravity Initiative, Jadwin Hall, Princeton University, Princeton, NJ 08544, USA

43 Data Science Institute, University of Arizona, 1230 North Cherry Avenue, Tucson, AZ 85721, USA

44 Program in Applied Mathematics, University of Arizona, 617 North Santa Rita, Tucson, AZ 85721, USA

45 Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, NY 14853, USA

46 Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, People's Republic of China

47 Key Laboratory of Radio Astronomy and Technology, Chinese Academy of Sciences, A20 Datun Road, Chaoyang District, Beijing, 100101, People's Republic of China

48 Korea Astronomy and Space Science Institute, Daedeok-daero 776, Yuseong-gu, Daejeon 34055, Republic of Korea

49 Department of Astronomy, Yonsei University, Yonsei-ro 50, Seodaemun-gu, 03722 Seoul, Republic of Korea

50 Physics Department, Fairfield University, 1073 North Benson Road, Fairfield, CT 06824, USA

51 Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801, USA

52 Instituto de Astronomía, Universidad Nacional Autónoma de México (UNAM), Apdo Postal 70-264, Ciudad de México, Mexico

53 Institut für Theoretische Physik, Goethe-Universität Frankfurt, Max-von-Laue-Straße 1, D-60438 Frankfurt am Main, Germany

54 Research Center for Astronomical Computing, Zhejiang Laboratory, Hangzhou 311100, People's Republic of China

55 Tsung-Dao Lee Institute, Shanghai Jiao Tong University, Shengrong Road 520, Shanghai, 201210, People's Republic of China

56 Department of Astronomy and Columbia Astrophysics Laboratory, Columbia University, 500 West 120th Street, New York, NY 10027, USA

57 Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Avenue, New York, NY 10010, USA

58 Dipartimento di Fisica "E. Pancini", Università di Napoli "Federico II", Compl. Univ. di Monte S. Angelo, Edificio G, Via Cinthia, I-80126, Napoli, Italy

59 INFN Sez. di Napoli, Compl. Univ. di Monte S. Angelo, Edificio G, Via Cinthia, I-80126, Napoli, Italy

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61 Department of Physics, University of Pretoria, Hatfield, Pretoria 0028, South Africa

62 Centre for Radio Astronomy Techniques and Technologies, Department of Physics and Electronics, Rhodes University, Makhanda 6140, South Africa

63 ASTRON, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands

64 LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, F-92195 Meudon, France

65 JILA and Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309, USA

66 National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100101, People's Republic of China

67 Las Cumbres Observatory, 6740 Cortona Drive, Suite 102, Goleta, CA 93117-5575, USA

68 Department of Physics, University of California, Santa Barbara, CA 93106-9530, USA

69 National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA

70 Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 32-D476, 77 Massachusetts Avenue, Cambridge, MA 02142, USA

71 Google Research, 355 Main Street, Cambridge, MA 02142, USA

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73 Department of History of Science, Harvard University, Cambridge, MA 02138, USA

74 Department of Physics, Harvard University, Cambridge, MA 02138, USA

75 NCSA, University of Illinois, 1205 West Clark Street, Urbana, IL 61801, USA

76 CP3-Origins, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark

77 Instituto Nacional de Astrofísica, Óptica y Electrónica. Apartado Postal 51 y 216, 72000. Puebla Pue., Mexico

78 Consejo Nacional de Humanidades, Ciencia y Tecnología, Av. Insurgentes Sur 1582, 03940, Ciudad de México, Mexico

79 Key Laboratory for Research in Galaxies and Cosmology, Chinese Academy of Sciences, Shanghai 200030, People's Republic of China

80 Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, 2-12 Hoshigaoka, Mizusawa, Oshu, Iwate 023-0861, Japan

81 Department of Astronomical Science, The Graduate University for Advanced Studies (SOKENDAI), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

82 NOVA Sub-mm Instrumentation Group, Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen, The Netherlands

83 Department of Astronomy, School of Physics, Peking University, Beijing 100871, People's Republic of China

84 Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, People's Republic of China

85 Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

86 The Institute of Statistical Mathematics, 10-3 Midori-cho, Tachikawa, Tokyo, 190-8562, Japan

87 Department of Statistical Science, The Graduate University for Advanced Studies (SOKENDAI), 10-3 Midori-cho, Tachikawa, Tokyo 190-8562, Japan

88 Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8583, Japan

89 Leiden Observatory, Leiden University, Postbus 2300, 9513 RA Leiden, The Netherlands

90 ASTRAVEO LLC, PO Box 1668, Gloucester, MA 01931, USA

91 Applied Materials Inc., 35 Dory Road, Gloucester, MA 01930, USA

92 Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA

93 University of Science and Technology, Gajeong-ro 217, Yuseong-gu, Daejeon 34113, Republic of Korea

94 Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8582, Japan

95 Joint Institute for VLBI ERIC (JIVE), Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands

96 Department of Astronomy and Atmospheric Sciences, Kyungpook National University, Daegu 702-701, Republic of Korea

97 Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea

98 Kogakuin University of Technology & Engineering, Academic Support Center, 2665-1 Nakano, Hachioji, Tokyo 192-0015, Japan

99 Graduate School of Science and Technology, Niigata University, 8050 Ikarashi 2-no-cho, Nishi-ku, Niigata 950-2181, Japan

100 Physics Department, National Sun Yat-Sen University, No. 70, Lien-Hai Road, Kaosiung City 80424, Taiwan, R.O.C.

101 School of Astronomy and Space Science, Nanjing University, Nanjing 210023, People's Republic of China

102 Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Nanjing 210023, People's Republic of China

103 INAF-Istituto di Radioastronomia, Via P. Gobetti 101, I-40129 Bologna, Italy

104 INAF-Istituto di Radioastronomia & Italian ALMA Regional Centre, Via P. Gobetti 101, I-40129 Bologna, Italy

105 Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Morelia 58089, Mexico

106 Yunnan Observatories, Chinese Academy of Sciences, 650011 Kunming, Yunnan Province, People's Republic of China

107 Center for Astronomical Mega-Science, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing, 100012, People's Republic of China

108 Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, 650011 Kunming, People's Republic of China

109 Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands

110 Gravitation and Astroparticle Physics Amsterdam (GRAPPA) Institute, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands

111 Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08544, USA

112 School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai, 200240, People's Republic of China

113 National Institute of Technology, Hachinohe College, 16-1 Uwanotai, Tamonoki, Hachinohe City, Aomori 039-1192, Japan

114 Research Center for Astronomy, Academy of Athens, Soranou Efessiou 4, 115 27 Athens, Greece

115 Department of Physics, Villanova University, 800 Lancaster Avenue, Villanova, PA 19085, USA

116 Physics Department, Washington University, CB 1105, St. Louis, MO 63130, USA

117 Departamento de Matemática da Universidade de Aveiro and Centre for Research and Development in Mathematics and Applications (CIDMA), Campus de Santiago, 3810-193 Aveiro, Portugal

118 School of Physics, Georgia Institute of Technology, 837 State Street NW, Atlanta, GA 30332, USA

119 School of Space Research, Kyung Hee University, 1732, Deogyeong-daero, Giheung-gu, Yongin-si, Gyeonggi-do 17104, Republic of Korea

120 Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8, Canada

121 Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada

122 Canadian Institute for Advanced Research, 180 Dundas Street West, Toronto, ON M5G 1Z8, Canada

123 Dipartimento di Fisica, Università di Trieste, I-34127 Trieste, Italy

124 INFN Sez. di Trieste, I-34127 Trieste, Italy

125 Department of Physics, National Taiwan Normal University, No. 88, Sec. 4, Tingzhou Road, Taipei 116, Taiwan, R.O.C.

126 Center of Astronomy and Gravitation, National Taiwan Normal University, No. 88, Sec. 4, Tingzhou Road, Taipei 116, Taiwan, R.O.C.

127 Gemini Observatory/NSF's NOIRLab, 670 North A'ohoku Place, Hilo, HI 96720, USA

128 Department of Physics, University of Toronto, 60 St. George Street, Toronto, ON M5S 1A7, Canada

129 Department of Physics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan

130 Hiroshima Astrophysical Science Center, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan

131 Aalto University Department of Electronics and Nanoengineering, PL 15500, FI-00076 Aalto, Finland

132 Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK

133 National Biomedical Imaging Center, Peking University, Beijing 100871, People's Republic of China

134 College of Future Technology, Peking University, Beijing 100871, People's Republic of China

135 Tokyo Electron Technology Solutions Limited, 52 Matsunagane, Iwayado, Esashi, Oshu, Iwate 023-1101, Japan

136 Department of Physics and Astronomy, University of Lethbridge, Lethbridge, AB T1K 3M4, Canada

137 Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai 980-8578, Japan

138 Astronomical Institute, Tohoku University, Sendai 980-8578, Japan

139 Department of Physics and Astronomy, Seoul National University, Gwanak-gu, Seoul 08826, Republic of Korea

140 University of New Mexico, Department of Physics and Astronomy, Albuquerque, NM 87131, USA

141 Physics Department, Brandeis University, 415 South Street, Waltham, MA 02453, USA

142 Tuorla Observatory, Department of Physics and Astronomy, University of Turku, Finland

143 Radboud Excellence Fellow of Radboud University, Nijmegen, The Netherlands

144 School of Natural Sciences, Institute for Advanced Study, 1 Einstein Drive, Princeton, NJ 08540, USA

145 School of Physics, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, People's Republic of China

146 Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK

147 Center for Astronomy and Astrophysics and Department of Physics, Fudan University, Shanghai 200438, People's Republic of China

148 Astronomy Department, University of Science and Technology of China, Hefei 230026, People's Republic of China

149 Department of Physics and Astronomy, Michigan State University, 567 Wilson Road, East Lansing, MI 48824, USA

Author notes

150 NASA Hubble Fellowship Program, Einstein Fellow.

151 Corresponding author.

Alexander W. Raymond https://orcid.org/0000-0002-5779-4767

Sheperd S. Doeleman https://orcid.org/0000-0002-9031-0904

Keiichi Asada https://orcid.org/0000-0001-6988-8763

Lindy Blackburn https://orcid.org/0000-0002-9030-642X

Geoffrey C. Bower https://orcid.org/0000-0003-4056-9982

Michael Bremer https://orcid.org/0000-0001-7511-3745

Dominique Broguiere https://orcid.org/0000-0001-9151-6683

Ming-Tang Chen https://orcid.org/0000-0001-6573-3318

Geoffrey B. Crew https://orcid.org/0000-0002-2079-3189

Sven Dornbusch https://orcid.org/0000-0003-3211-3352

Vincent L. Fish https://orcid.org/0000-0002-7128-9345

Roberto García https://orcid.org/0000-0002-6584-7443

Olivier Gentaz https://orcid.org/0000-0002-0115-4605

Ciriaco Goddi https://orcid.org/0000-0002-2542-7743

Michael H. Hecht https://orcid.org/0000-0002-4114-4583

Yau-De Huang https://orcid.org/0000-0001-8783-6211

Michael Janssen https://orcid.org/0000-0001-8685-6544

Garrett K. Keating https://orcid.org/0000-0002-3490-146X

Jun Yi Koay https://orcid.org/0000-0002-7029-6658

Thomas P. Krichbaum https://orcid.org/0000-0002-4892-9586

Wen-Ping Lo https://orcid.org/0000-0003-1869-2503

Satoki Matsushita https://orcid.org/0000-0002-2127-7880

Lynn D. Matthews https://orcid.org/0000-0002-3728-8082

James M. Moran https://orcid.org/0000-0002-3882-4414

Nimesh Patel https://orcid.org/0000-0002-6021-9421

Dominic W. Pesce https://orcid.org/0000-0002-5278-9221

Venkatessh Ramakrishnan https://orcid.org/0000-0002-9248-086X

Alan L. Roy https://orcid.org/0000-0002-1931-0135

Salvador Sánchez https://orcid.org/0000-0002-8042-5951

Remo P. J. Tilanus https://orcid.org/0000-0002-6514-553X

Michael Titus https://orcid.org/0000-0001-9001-3275

Pablo Torne https://orcid.org/0000-0001-8700-6058

Jan Wagner https://orcid.org/0000-0003-1105-6109

Jonathan Weintroub https://orcid.org/0000-0002-4603-5204

Maciek Wielgus https://orcid.org/0000-0002-8635-4242

André Young https://orcid.org/0000-0003-0000-2682

Kazunori Akiyama https://orcid.org/0000-0002-9475-4254

Ezequiel Albentosa-Ruíz https://orcid.org/0000-0002-7816-6401

Antxon Alberdi https://orcid.org/0000-0002-9371-1033

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Michi Bauböck https://orcid.org/0000-0002-5518-2812

Bradford A. Benson https://orcid.org/0000-0002-5108-6823

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Katherine L. Bouman https://orcid.org/0000-0003-0077-4367

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Roger Brissenden https://orcid.org/0000-0002-2556-0894

Silke Britzen https://orcid.org/0000-0001-9240-6734

Avery E. Broderick https://orcid.org/0000-0002-3351-760X

Thomas Bronzwaer https://orcid.org/0000-0003-1151-3971

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Andrew Chael https://orcid.org/0000-0003-2966-6220

Chi-kwan Chan https://orcid.org/0000-0001-6337-6126

Dominic O. Chang https://orcid.org/0000-0001-9939-5257

Koushik Chatterjee https://orcid.org/0000-0002-2825-3590

Shami Chatterjee https://orcid.org/0000-0002-2878-1502

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Xiaopeng Cheng https://orcid.org/0000-0003-4407-9868

Ilje Cho https://orcid.org/0000-0001-6083-7521

Pierre Christian https://orcid.org/0000-0001-6820-9941

Nicholas S. Conroy https://orcid.org/0000-0003-2886-2377

John E. Conway https://orcid.org/0000-0003-2448-9181

Thomas M. Crawford https://orcid.org/0000-0001-9000-5013

Alejandro Cruz-Osorio https://orcid.org/0000-0002-3945-6342

Yuzhu Cui https://orcid.org/0000-0001-6311-4345

Rohan Dahale https://orcid.org/0000-0001-6982-9034

Jordy Davelaar https://orcid.org/0000-0002-2685-2434

Mariafelicia De Laurentis https://orcid.org/0000-0002-9945-682X

Roger Deane https://orcid.org/0000-0003-1027-5043

Jessica Dempsey https://orcid.org/0000-0003-1269-9667

Gregory Desvignes https://orcid.org/0000-0003-3922-4055

Jason Dexter https://orcid.org/0000-0003-3903-0373

Vedant Dhruv https://orcid.org/0000-0001-6765-877X

Indu K. Dihingia https://orcid.org/0000-0002-4064-0446

Sergio A. Dzib https://orcid.org/0000-0001-6010-6200

Ralph P. Eatough https://orcid.org/0000-0001-6196-4135

Razieh Emami https://orcid.org/0000-0002-2791-5011

Heino Falcke https://orcid.org/0000-0002-2526-6724

Joseph Farah https://orcid.org/0000-0003-4914-5625

Edward Fomalont https://orcid.org/0000-0002-9036-2747

H. Alyson Ford https://orcid.org/0000-0002-9797-0972

Marianna Foschi https://orcid.org/0000-0001-8147-4993

Raquel Fraga-Encinas https://orcid.org/0000-0002-5222-1361

Per Friberg https://orcid.org/0000-0002-8010-8454

Christian M. Fromm https://orcid.org/0000-0002-1827-1656

Antonio Fuentes https://orcid.org/0000-0002-8773-4933

Peter Galison https://orcid.org/0000-0002-6429-3872

Charles F. Gammie https://orcid.org/0000-0001-7451-8935

Boris Georgiev https://orcid.org/0000-0002-3586-6424

Roman Gold https://orcid.org/0000-0003-2492-1966

Arturo I. Gómez-Ruiz https://orcid.org/0000-0001-9395-1670

José L. Gómez https://orcid.org/0000-0003-4190-7613

Minfeng Gu https://orcid.org/0000-0002-4455-6946

Mark Gurwell https://orcid.org/0000-0003-0685-3621

Kazuhiro Hada https://orcid.org/0000-0001-6906-772X

Daryl Haggard https://orcid.org/0000-0001-6803-2138

Ronald Hesper https://orcid.org/0000-0003-1918-6098

Dirk Heumann https://orcid.org/0000-0002-7671-0047

Luis C. Ho https://orcid.org/0000-0001-6947-5846

Paul Ho https://orcid.org/0000-0002-3412-4306

Mareki Honma https://orcid.org/0000-0003-4058-9000

Chih-Wei L. Huang https://orcid.org/0000-0001-5641-3953

Lei Huang https://orcid.org/0000-0002-1923-227X

Shiro Ikeda https://orcid.org/0000-0002-2462-1448

C. M. Violette Impellizzeri https://orcid.org/0000-0002-3443-2472

Makoto Inoue https://orcid.org/0000-0001-5037-3989

Sara Issaoun https://orcid.org/0000-0002-5297-921X

David J. James https://orcid.org/0000-0001-5160-4486

Buell T. Jannuzi https://orcid.org/0000-0002-1578-6582

Britton Jeter https://orcid.org/0000-0003-2847-1712

Wu Jiang https://orcid.org/0000-0001-7369-3539

Alejandra Jiménez-Rosales https://orcid.org/0000-0002-2662-3754

Michael D. Johnson https://orcid.org/0000-0002-4120-3029

Svetlana Jorstad https://orcid.org/0000-0001-6158-1708

Abhishek V. Joshi https://orcid.org/0000-0002-2514-5965

Taehyun Jung https://orcid.org/0000-0001-7003-8643

Ramesh Karuppusamy https://orcid.org/0000-0002-5307-2919

Tomohisa Kawashima https://orcid.org/0000-0001-8527-0496

Mark Kettenis https://orcid.org/0000-0002-6156-5617

Dong-Jin Kim https://orcid.org/0000-0002-7038-2118

Jae-Young Kim https://orcid.org/0000-0001-8229-7183

Jongsoo Kim https://orcid.org/0000-0002-1229-0426

Junhan Kim https://orcid.org/0000-0002-4274-9373

Motoki Kino https://orcid.org/0000-0002-2709-7338

Prashant Kocherlakota https://orcid.org/0000-0001-7386-7439

Patrick M. Koch https://orcid.org/0000-0003-2777-5861

Shoko Koyama https://orcid.org/0000-0002-3723-3372

Carsten Kramer https://orcid.org/0000-0002-4908-4925

Joana A. Kramer https://orcid.org/0009-0003-3011-0454

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Michael Lindqvist https://orcid.org/0000-0002-3669-0715

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Jun Liu https://orcid.org/0000-0002-7615-7499

Kuo Liu https://orcid.org/0000-0002-2953-7376

Elisabetta Liuzzo https://orcid.org/0000-0003-0995-5201

Andrei P. Lobanov https://orcid.org/0000-0003-1622-1484

Laurent Loinard https://orcid.org/0000-0002-5635-3345

Colin J. Lonsdale https://orcid.org/0000-0003-4062-4654

Amy E. Lowitz https://orcid.org/0000-0002-4747-4276

Ru-Sen Lu https://orcid.org/0000-0002-7692-7967

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Sera Markoff https://orcid.org/0000-0001-9564-0876

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Monika Moscibrodzka https://orcid.org/0000-0002-4661-6332

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Ioannis Myserlis https://orcid.org/0000-0003-3025-9497

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Masanori Nakamura https://orcid.org/0000-0001-6081-2420

Gopal Narayanan https://orcid.org/0000-0002-4723-6569

Iniyan Natarajan https://orcid.org/0000-0001-8242-4373

Antonios Nathanail https://orcid.org/0000-0002-1655-9912

Joey Neilsen https://orcid.org/0000-0002-8247-786X

Chunchong Ni https://orcid.org/0000-0003-1361-5699

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Junghwan Oh https://orcid.org/0000-0002-4991-9638

Hiroki Okino https://orcid.org/0000-0003-3779-2016

Héctor Raúl Olivares Sánchez https://orcid.org/0000-0001-6833-7580

Tomoaki Oyama https://orcid.org/0000-0003-4046-2923

Feryal Özel https://orcid.org/0000-0003-4413-1523

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Jongho Park https://orcid.org/0000-0001-6558-9053

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Giacomo Principe https://orcid.org/0000-0003-0406-7387

Dimitrios Psaltis https://orcid.org/0000-0003-1035-3240

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Ramprasad Rao https://orcid.org/0000-0002-1407-7944

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Chet Ruszczyk https://orcid.org/0000-0001-7278-9707

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Miguel Sánchez-Portal https://orcid.org/0000-0003-0981-9664

Mahito Sasada https://orcid.org/0000-0001-5946-9960

Kaushik Satapathy https://orcid.org/0000-0003-0433-3585

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Jonathan Schonfeld https://orcid.org/0000-0002-8909-2401

Karl-Friedrich Schuster https://orcid.org/0000-0003-2890-9454

Lijing Shao https://orcid.org/0000-0002-1334-8853

Zhiqiang Shen https://orcid.org/0000-0003-3540-8746

Des Small https://orcid.org/0000-0003-3723-5404

Bong Won Sohn https://orcid.org/0000-0002-4148-8378

Jason SooHoo https://orcid.org/0000-0003-1938-0720

León David Sosapanta Salas https://orcid.org/0000-0003-1979-6363

Kamal Souccar https://orcid.org/0000-0001-7915-5272

Joshua S. Stanway https://orcid.org/0009-0003-7659-4642

He Sun https://orcid.org/0000-0003-1526-6787

Fumie Tazaki https://orcid.org/0000-0003-0236-0600

Alexandra J. Tetarenko https://orcid.org/0000-0003-3906-4354

Paul Tiede https://orcid.org/0000-0003-3826-5648

Kenji Toma https://orcid.org/0000-0002-7114-6010

Teresa Toscano https://orcid.org/0000-0003-3658-7862

Efthalia Traianou https://orcid.org/0000-0002-1209-6500

Sascha Trippe https://orcid.org/0000-0003-0465-1559

Matthew Turk https://orcid.org/0000-0002-5294-0198

Ilse van Bemmel https://orcid.org/0000-0001-5473-2950

Huib Jan van Langevelde https://orcid.org/0000-0002-0230-5946

Daniel R. van Rossum https://orcid.org/0000-0001-7772-6131

Jesse Vos https://orcid.org/0000-0003-3349-7394

Derek Ward-Thompson https://orcid.org/0000-0003-1140-2761

John Wardle https://orcid.org/0000-0002-8960-2942

Jasmin E. Washington https://orcid.org/0000-0002-7046-0470

Robert Wharton https://orcid.org/0000-0002-7416-5209

Kaj Wiik https://orcid.org/0000-0002-0862-3398

Gunther Witzel https://orcid.org/0000-0003-2618-797X

Michael F. Wondrak https://orcid.org/0000-0002-6894-1072

George N. Wong https://orcid.org/0000-0001-6952-2147

Qingwen Wu https://orcid.org/0000-0003-4773-4987

Nitika Yadlapalli https://orcid.org/0000-0003-3255-4617

Paul Yamaguchi https://orcid.org/0000-0002-6017-8199

Aristomenis Yfantis https://orcid.org/0000-0002-3244-7072

Doosoo Yoon https://orcid.org/0000-0001-8694-8166

Ziri Younsi https://orcid.org/0000-0001-9283-1191

Wei Yu https://orcid.org/0000-0002-5168-6052

Feng Yuan https://orcid.org/0000-0003-3564-6437

Ye-Fei Yuan https://orcid.org/0000-0002-7330-4756

J. Anton Zensus https://orcid.org/0000-0001-7470-3321

Shuo Zhang https://orcid.org/0000-0002-2967-790X

Guang-Yao Zhao https://orcid.org/0000-0002-4417-1659

Shan-Shan Zhao https://orcid.org/0000-0002-9774-3606

• Received 2024 April 30
• Revised 2024 June 23
• Accepted 2024 June 24
• Published 2024 August 27

Very long baseline interferometry ; Radio interferometry ; Black holes ; Supermassive black holes ; High angular resolution ; Astronomical techniques ; Event horizons

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The first very long baseline interferometry (VLBI) detections at 870 μ m wavelength (345 GHz frequency) are reported, achieving the highest diffraction-limited angular resolution yet obtained from the surface of the Earth and the highest-frequency example of the VLBI technique to date. These include strong detections for multiple sources observed on intercontinental baselines between telescopes in Chile, Hawaii, and Spain, obtained during observations in 2018 October. The longest-baseline detections approach 11 G λ , corresponding to an angular resolution, or fringe spacing, of 19 μ as. The Allan deviation of the visibility phase at 870 μ m is comparable to that at 1.3 mm on the relevant integration timescales between 2 and 100 s. The detections confirm that the sensitivity and signal chain stability of stations in the Event Horizon Telescope (EHT) array are suitable for VLBI observations at 870 μ m. Operation at this short wavelength, combined with anticipated enhancements of the EHT, will lead to a unique high angular resolution instrument for black hole studies, capable of resolving the event horizons of supermassive black holes in both space and time.

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1. Introduction

The technique of very long baseline interferometry (VLBI) involves a network of independently clocked telescopes separated by large distances, which simultaneously observe a common astronomical source (Thompson et al. 2017 ). The angular resolution, or fringe spacing, in a VLBI observation scales inversely with both the distance between stations (i.e., the length of the baseline) and the observing frequency. The present article reports the first fringe detections made at 870 μ m wavelength (345 GHz nominal frequency), which constitutes the shortest-wavelength VLBI observation to date. The experiment we describe was intended as a first technical demonstration of the 870 μ m VLBI capability using facilities that are part of the Event Horizon Telescope (EHT) array. Figure 1 shows the stations that participated in the fringe test along with the usual metric used to characterize millimeter-wavelength observing conditions: the 225 GHz zenith opacity (Thompson et al. 2017 ).

Figure 1.  (Top) Stations in the 870 μ m fringe test. (Bottom) Zenith opacity at 225 GHz, which is the standard frequency used for monitoring millimeter-wave conditions. The observing window on each day is indicated by the green shading. Conditions at ALMA were very good during both days ( τ 225 ≈ 0.05). The black lines indicate the opacity at each site calculated using inputs from MERRA-2 reanalysis during the observing windows, which we use to estimate 870 μ m (345 GHz) opacity. Opacities for APEX and NOEMA have been estimated by converting precipitable water vapor column amounts.

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The VLBI observing wavelength has decreased over time. The first 3 mm VLBI detections (at 86 GHz) were obtained through observations performed in 1981 (Readhead et al. 1983 ), the first 3 mm intercontinental detections (100 GHz) were obtained through observations performed in 1988 (Baath et al. 1991 , 1992 ), and the first successful 1.3 mm (230 GHz) VLBI was carried out in 1989 (Padin et al. 1990 ). The especially long time since the last significant decrease in VLBI wavelength reflects the challenges of carrying out such observations, which are detailed below. Even so, there have been several milestones of note since the early 1990s on the path toward developing short-wavelength VLBI as an important technique for astrophysics. Increased sensitivity through the use of larger telescopes and advanced receivers led to 1.4 mm (215 GHz) detections on a ∼1100 km baseline of multiple active galactic nuclei (AGN) and Sagittarius A* (Sgr A*), the Galactic center supermassive black hole (Greve et al. 1995 ; Krichbaum et al. 1997 , 1998 ). A return to the longer-wavelength 2 mm spectral windows (147 GHz and 129 GHz) allowed extension of millimeter-wavelength VLBI to intercontinental baselines (Doeleman et al. 2002 ; Greve et al. 2002 ; Krichbaum et al. 2002 ). Building on this work, Doeleman et al. ( 2008 , 2012 ) used purpose-built wideband digital VLBI systems on 1.3 mm transoceanic baselines to report the discovery of event-horizon-scale structures in Sgr A* and the much more massive black hole, M87*. The EHT collaboration has now imaged both of these sources with a global 1.3 mm VLBI array (Event Horizon Telescope Collaboration et al. 2019a , 2022a , 2024 ).

The EHT is the highest-resolution ground-based VLBI instrument to date (Event Horizon Telescope Collaboration et al. 2019b ). The EHT fringe spacing is approximately 25 μ as at 1.3 mm wavelength. The finite diameter of the Earth limits ground-based 1.3 mm fringe spacing to 21 μ as, corresponding to a 9.8 G λ baseline. In practice, modern imaging methods, such as regularized maximum likelihood, achieve a slightly higher angular resolution that exceeds the diffraction limit (Event Horizon Telescope Collaboration et al. 2019c ).

For future campaigns, the EHT has developed the capability to observe at 870 μ m, and enhancing the ability to observe at this wavelength through new stations and wider bandwidth is an important aspect of long-term enhancements envisaged by the next-generation EHT (ngEHT) project (Doeleman et al. 2019 , 2023 ; Raymond et al. 2021 ). For a given set of station locations, observing at 870 μ m improves angular resolution by approximately 50% compared to observing at 1.3 mm, which will provide a sharper view of the black hole shadow and environment; the 870 μ m fringe spacing limit set by the diameter of the Earth is approximately 14 μ as, corresponding to a 14.7 G λ baseline. Observations at 870 μ m are also important for polarimetric measurements. Faraday rotation, which scrambles the imaged electric field vector position angle pattern, diminishes with the square of the frequency. Therefore, 870 μ m observations may help distinguish Faraday rotation from the intrinsic field pattern set by the horizon-scale magnetic field and plasma properties (Event Horizon Telescope Collaboration et al. 2021 ; Wielgus et al. 2024 ). For Sgr A*, the angular size of the black hole shadow is larger than that of M87* (Event Horizon Telescope Collaboration et al. 2022a ), but scattering in the ionized interstellar medium affects the image angular resolution (see, e.g., Johnson et al. 2018 ). At 1.3 mm, the scatter broadening is comparable to the current EHT resolution, but it decreases approximately as the observing wavelength squared. Thus, at 870 μ m, scattering effects would be significantly diminished and would not limit the resolution of a VLBI array for studies of Sgr A*. In particular, extension of the EHT to 870 μ m wavelengths can target photon ring substructure in Sgr A*, aiming to detect the orbit of light that makes a full "u-turn" around the black hole (Johnson et al. 2020 ; Palumbo et al. 2023 ). For these reasons, 870 μ m VLBI opens important new directions for advanced horizon-resolved studies of the two primary EHT sources. At the same time, higher-frequency VLBI brings more sources into range for horizon-resolved black hole studies (Pesce et al. 2021 ; Lo et al. 2023 ; Ramakrishnan et al. 2023 ), and the increased resolution at 870 μ m benefits nonhorizon VLBI studies of AGN jets (e.g., Kim et al. 2020 ; Janssen et al. 2021 ; Issaoun et al. 2022 ; Jorstad et al. 2023 ; Paraschos et al. 2024 ). Additionally, due to reduced opacity, shorter wavelengths probe more compact regions of jetted AGN sources (an example being the core-shift effect; Lobanov 1998 ; Hada et al. 2011 ). Hence, 870 μ m VLBI has the potential to image the jet launching region closer to the central black hole, enabling investigations of the physics behind jet formation, collimation, and acceleration. In particular, the poorly understood limb brightening in transversely resolved inner jets (e.g., Janssen et al. 2021 ) can be studied in much greater detail.

Extension of observing to 870 μ m similarly enhances the capability of the EHT to capture dynamics near the event horizon. In the case of Sgr A*, the dynamical timescale is ∼200 s (10 GM / c 3 ). Simultaneous 1.3 mm and 870 μ m observing can sample sufficient Fourier spatial frequencies within this integration time to allow snapshot imaging using the technique of multifrequency synthesis (MFS; Chael et al. 2023 ). Combining such snapshots will enable recovery of accretion and jet launching kinematics. For M87*, the dynamical timescale is ∼3 days, and data obtained in both 1.3 mm and 870 μ m on sequential days can be combined to form high-fidelity MFS images for time-lapse movie reconstruction of the event horizon environment. Realizing the full scientific potential of 870 μ m VLBI (Johnson et al. 2023 ) will require the planned ngEHT upgrade (Doeleman et al. 2023 ).

While there are clearly many motivating reasons for 870 μ m VLBI observing, a number of factors make the measurements difficult in this short-wavelength regime. The atmosphere is more opaque at 870 μ m than at 1.3 mm (see, for example, Liebe 1985 ; Matsushita et al. 1999 , 2016 , 2022 ), which means that sources are more attenuated and noise levels due to atmospheric emission are elevated. Overall, the effective system temperatures of coherent radio receivers are intrinsically greater at 870 μ m than at 1.3 mm. 152 The aperture efficiency of the collecting optics tends to diminish at high frequency, and the source flux density tends to decrease. In addition, coherence losses due to the VLBI frequency standards used at each site increase with observing frequency (Doeleman et al. 2011 ). The EHT array, conceived as a common, international effort of independent observatories working in the short-millimeter range, has directly addressed these challenges and provides key enabling infrastructure for extension of VLBI to higher frequencies (Event Horizon Telescope Collaboration et al. 2019b ).

The telescopes comprising the EHT array are precision structures sited at high-altitude, low-opacity locations (see, e.g., Levy et al. 1996 ; Mangum et al. 2006 ; Greve & Bremer 2010 ; Chen et al. 2023 and references therein on the design and qualification of such instruments). State-of-the-art instrumentation underpinning the operation of these telescopes, as single-dish facilities and for VLBI, includes cryogenic receivers and wideband digital backends—all refined over many years to optimize performance at millimeter and submillimeter wavelengths. Steady improvements in superconductor–insulator–superconductor junctions have formed the basis for increased bandwidth and sensitivity of millimeter and submillimeter receivers, leading to state-of-the-art systems in use at EHT sites (see Maier et al. 2005 , 2012 ; Tong et al. 2005 , 2013 ; Chenu et al. 2007 , 2016 ; Carter et al. 2012 ; Mahieu et al. 2012 ; Kerr et al. 2014 ; Klein et al. 2014 ; Belitsky et al. 2018 ; Han et al. 2018 ).

Following the successful 1.3 mm VLBI observations in 2017, test observations at 870 μ m were conducted on the EHT array in 2018 October. Conditions at the Atacama Large Millimeter/submillimeter Array (ALMA) station during this test, including characterization of the system used there to phase the array for VLBI, are described in Crew et al. ( 2023 ). The present paper describes the VLBI test observations

2.1. Schedule

The 870 μ m fringe test observations consisted of two short scheduling blocks designed for two different subarrays. An eastern subarray, comprising ALMA, the Atacama Pathfinder EXperiment (APEX), the Greenland Telescope (GLT), the Institut de Radioastronomie Millimétrique 30 m telescope (IRAM30m), and the Northern Extended Millimeter Array (NOEMA), was scheduled to include blazar sources that were visible in the nighttime hours at all sites: CTA 102, 3C 454.3 , and BL Lac. A western subarray, comprising ALMA, APEX, GLT, and the Submillimeter Array (SMA), observed quasars J0423−0120, J0510+1800 , J0521+1638 , and J0522−3627 . The eastern subarray scheduling block was followed by several scans on BL Lac at 1.3 mm wavelength to aid diagnosis in the event of a null result. Schedule blocks for both subarrays were optimized for fringe detection at 870 μ m VLBI, and they spanned a duration of between 1 and 2 hr with at least two scans on every source. Most scans lasted 5 minutes.

The observing window consisted of five nights, 2018 October 17–21, between approximately midnight and 2:00 Coordinated Universal Time (UTC) for the eastern subarray scheduling block and between 9:00 and 11:00 UTC for the western subarray scheduling block. Each scheduling block was triggered twice within the observing window. We report herein on successful observations with the eastern array on 2018 October 18–19 and with the western array on 2018 October 21. Details of the scheduling blocks and sources observed are shown in Figure 2 .

Figure 2.  870 μ m observations that yielded detections were made during two separate scheduling blocks: 2018 October 18/19 and 2018 October 21. The observations on the first night were done with an eastern array comprising ALMA, APEX, GLT, IRAM30m, and NOEMA. Observations on the second night were made with a western array: ALMA, APEX, GLT, and SMA. The scheduling blocks for both nights are shown along with the one-letter station codes, which are listed in parentheses. All detections are on baselines involving ALMA. The scans that yielded detections on baselines defined by a given station are indicated by the white horizontal ticks centered in each time block: from the top, ticks correspond to XL, XR, YL, and YR mixed polarizations per the legend at upper right. The absence of a tick indicates a nondetection. Three scans at 230 GHz (1.3 mm) were performed at the end of the eastern subarray scheduling block using just the IRAM30m and ALMA facilities.

2.2. Instrumentation and Array

Several important technologies developed for 1.3 mm VLBI are leveraged to address the challenges of 870 μ m observing, many of which are outlined in Event Horizon Telescope Collaboration et al. ( 2019b ). The VLBI backends, used to condition and digitize signals from the telescope receivers, have a cumulative data rate of 64 Gbps (Vertatschitsch et al. 2015 ; Tuccari et al. 2017 ) across four 2 GHz wide bands and two polarizations. Each station is outfitted with a hydrogen maser time standard, which had previously been found to be sufficiently stable for timekeeping in a 1.3 mm VLBI experiment and was expected to be sufficiently stable for 870 μ m.

Phased array beamforming capability is implemented at both the SMA (Young et al. 2016 ) and ALMA (Matthews et al. 2018 ) array stations. For both these stations, beamformer phasing efficiency at 870 μ m, which directly scales the visibility amplitudes measured on baselines to the station, varied from just below 50% to as high as about 80%. These efficiencies are less than what is typical for 1.3 mm (Event Horizon Telescope Collaboration et al. 2019b ). Section 3.4 has a discussion relevant to ALMA, SMA, and NOEMA 153 of phasing efficiency challenges and planned improvements to mitigate these.

The frequency setup for the 870 μ m fringe test is similar to that described in Table 4 of Event Horizon Telescope Collaboration et al. ( 2019b ). Most stations in the array observed a single 2048 MHz band at a 4–6 GHz intermediate frequency (IF) using a 342.6 GHz sky local oscillator (LO). 154 That frequency setup corresponds to a sky frequency range of 346.552–348.6 GHz. Each station observed both circular polarizations, with the exceptions of APEX (right-circular polarization only) and ALMA (dual linear, X and Y). The recorded station data were correlated using DiFX software (Deller et al. 2011 ) at the MIT Haystack Observatory. Visibility data on baselines to ALMA remained on a mixed-polarization basis (i.e., {X, Y} × {L, R}) because the observing schedules were not long enough to track polarization calibrators over a wide range of parallactic angles, which is necessary for converting the ALMA data from a linear to a circular basis (Martí-Vidal et al. 2016 ; Matthews et al. 2018 ; Goddi et al. 2019 ). Subsequent fringe fitting was done using the Haystack Observatory Postprocessing System (HOPS 155 ; Whitney et al. 2004 ; see also Blackburn et al. 2019 ).

2.2.1. ALMA

ALMA observed in dual linear polarization with IRAM-designed 870 μ m (i.e., Band 7) cartridges (Mahieu et al. 2012 ). The ALMA Phasing System (APS; Matthews et al. 2018 ) was used to aggregate the collecting area of the active dishes in the ALMA array. The APS capability had been used previously for VLBI science at 3 mm (Issaoun et al. 2019 ; Okino et al. 2022 ; Zhao et al. 2022 ) and 1.3 mm (Event Horizon Telescope Collaboration et al. 2019a , 2019b ) but not at shorter wavelengths, albeit the setup for 870 μ m observations is similar to the longer-wavelength bands. In the 870 μ m experiment, the four recorded 2.048 GHz subbands were tuned to center frequencies of 335.6, 337.541406, 347.6, and 349.6 GHz. The choice of the 337.541406 GHz frequency results from ALMA-specific tuning restrictions.

The ALMA phased array included 25 12 m antennas during the eastern track and 29 12 m antennas during the western track with a maximum antenna spacing of 600 m in both cases. Wind speeds were greater than 10 m s −1 at the ALMA site. During the eastern track, the phasing efficiency was below 50% for most of the time and at best was about 80%. During the October 21 track (western) in better weather, the phasing efficiency was more stable and greater than approximately 90% (Crew et al. 2023 ).

2.2.2. APEX

The APEX and ALMA stations are colocated, and conditions were similar at the two telescopes. APEX observed using the 345 GHz FLASH+ linear receiver (Klein et al. 2014 ). That receiver may not have been functioning optimally during the experiment and has since been replaced by the Swedish-ESO PI Instrument for APEX (Belitsky et al. 2018 ; Meledin et al. 2022 ). A quarter wave plate was used to achieve circular polarization. Two backends, a ROACH2 Digital Backend (R2DBE; Vertatschitsch et al. 2015 ) and a Digital BaseBand Converter 3 (Tuccari et al. 2017 ), were operated in parallel.

The GLT station participated in the observation but at the time was still commissioning specific subsystems. The GLT antenna has operated at Pituffik Space Base, formerly the Thule Airbase site, in Greenland since 2017 August (Inoue et al. 2014 ; Raffin et al. 2016 ; Matsushita et al. 2018 ; Koay et al. 2020 ; Chen et al. 2023 ). The GLT observed in dual linear polarization with the IRAM-made 870 μ m (i.e., Band 7) cartridges (Mahieu et al. 2012 ). The 345 GHz receiver on the GLT saw first light in continuum and spectral-line modes in 2018 August. Pointing and focus calibration at 345 GHz were still in the commissioning phase during the 870 μ m observation reported here. The GLT pointing system has since been fully commissioned for recent and future VLBI observing. Similarly, final adjustments to the dish surface had yet to be made, and the surface accuracy was estimated to be 170 μ m rms during the observations reported here. Subsequent improvements have led to rms surface accuracy in the 17–40 μ m range (see Table 7 in Chen et al. 2023 ).

2.2.4. IRAM30m

The IRAM30m telescope used the heterodyne Eight MIxer Receiver (Carter et al. 2012 ) in the 870 μ m band also known as E330. The setup and preobserving checks were analogous to a regular Global Millimeter VLBI Array or EHT session. The opacity at 870 μ m during the scheduled VLBI observations was high and would not typically have triggered single-dish science operation at this wavelength.

2.2.5. NOEMA

Portions of the NOEMA station were still being commissioned during the 870 μ m experiment. NOEMA observed in dual polarization as a single-antenna station, not as a phased array. The NOEMA receiver was a dual-polarization single-sideband unit (Chenu et al. 2016 ) with a 4 GHz bandpass. Recording was with a 16 Gbps R2DBE. The NOEMA phased array has since been commissioned for VLBI observing.

The SMA station observed with seven antennas arranged in the compact configuration with a maximum baseline of 69.1 m. The SMA Wideband Astronomical ROACH2 Machine (SWARM; Primiani et al. 2016 ; Young et al. 2016 ) was run with the VLBI beamformer mode activated, producing a coherent phased array sum of the seven antennas formatted for VLBI recording. As expected, the phasing efficiency was lower than for 1.3 mm operations. The sky LO was set to 341.6 GHz, not 342.6 GHz, to match the SWARM sky coverage with the other stations, compensating for a different IF to baseband LO because SWARM uses its own block downconverter rather than the standard EHT single-dish equipment. The data were recorded in the frequency domain at the standard SMA clock rate (4.576 Gsps), which differs from the standard EHT single-dish sample rate of 4.096 Gsps (Vertatschitsch et al. 2015 ). Adaptive Phased Array Interpolating Downsampler for SWARM (APHIDS) postprocessing was completed to interpolate and invert (from frequency domain to time domain) the SWARM data sets in preparation for VLBI correlation. After APHIDS processing, the SMA EHT data product matches that produced by the standard SMA single-dish station in sample rate and is also a time series matching the standard EHT single-dish data product.

3. Results and Discussion

Figure 1 shows that the conditions during the experiment were mixed across the array. While the observatories do not measure 870 μ m (345 GHz) opacity directly, we use MERRA-2 reanalysis and radiative transfer (Paine 2022 ) that is validated by measurements at 225 GHz (Figure 1 , black lines) to estimate τ 345 . For the eastern subarray on October 18/19, τ 345 was 0.2 at the ALMA and APEX sites and 0.8 at IRAM30m. For the western subarray on October 21, τ 345 was approximately 0.17 at the ALMA and APEX sites and 0.7 at SMA. During the experiment, the opacities at GLT and NOEMA were unfavorable, and detections on baselines to those stations were not achieved; however, both stations have weather that is compatible with 870 μ m observing and will likely yield high-frequency detections in the future (see, e.g., Raymond et al. 2021 ; Matsushita et al. 2022 ). Atmospheric conditions can change rapidly: τ 225 at the SMA decreased by nearly a factor of 4 in the hours following the experiment.

3.1. 870 μ m (345 GHz) Fringes

In VLBI, recorded data from all sites are brought to a central processing facility where data streams from each pair of sites are cross-correlated. The resulting complex correlation quantities provide a dimensionless measure of the electric field coherence between the two sites, which is proportional to a Fourier component of the brightness distribution of the target source. The correlation processor uses an a priori model to align the site data streams, recreating the exact geometry of the physical baseline connecting the two sites at the time of observation. Because the a priori model is imperfect, after processing, the cross-correlation phase typically varies as a function of time and frequency due to residual delay and delay rate, respectively. To average the correlation signal over frequency and time, the correlator output is thus searched over a range of delay and delay rate to find a peak in correlator power—a process also known as "fringe fitting" (Thompson et al. 2017 ). In this experiment, the correlator output was searched by dividing each scan into short segments and incoherently averaging them. The incoherent averaging technique (Rogers et al. 1995 ) estimates noise-debiased VLBI quantities, and it is well suited to processing low signal-to-noise ratio (S/N) VLBI data on sparse arrays as it allows integration beyond the nominal atmospheric coherence time. Figure 3 shows the dependence of amplitude in units of 10 4 and S/N on the duration of the segments for a sample scan on source J0423−0120 for the baseline comprising the ALMA and SMA stations. All four cross-hand polarizations are plotted. The scan identifier 294–0938 in Figure 3 corresponds to the day UTC for the beginning of the scan, where the day is the number of days since 2018 January 1 (294 is October 21) and UTC is the scan start time. The noise-debiased amplitude (Rogers et al. 1995 ) in Figure 3 is indicated by the horizontal blue dashed line. As the segment duration decreases, the effect of decoherence is reduced, so the S/N increases.

Figure 3.  Scan-averaged and noise-debiased 870 μ m fringe amplitude (open blue circles, left axes) and S/N (filled red squares, right axes). Amplitudes and S/N are computed by first dividing each observing scan into short coherently integrated segments, which are then combined incoherently following the procedure in Rogers et al. ( 1995 ). Segment length is shown on the horizontal axis. Each subplot shows a different polarization on the ALMA–SMA baseline for a single scan on J0423−0120 (October 21, 09:38 UTC). Other detections listed in Table 1 have a similar dependence on segment duration but generally lower S/N. The noise-debiased amplitude and coherence time were derived using HOPS and are indicated by the horizontal blue dashed line and the vertical solid black line, respectively.

Compared to a single coherent integration over a full scan (approximately 300 s in most of the measurements), incoherently averaging the parts of a segmented scan increases the S/N by up to a factor of 2 on many of the measurements, yielding higher confidence in the detections. For most of the measurements, S/N values asymptote at the shortest segment durations. Ordinarily, we would expect the S/N values to decrease as the segments are shortened below the coherence time. The behavior we observe could be indicative of a changing coherence during the scan consistent with the windy conditions at ALMA (Crew et al. 2023 ).

Contours of fringe power versus multiband delay and rate are plotted in Figure 4 for a single scan of J0423−0120 on the ALMA–SMA baseline. The measurement exhibits a definitive peak in fringe power for each of the cross-hand polarizations. The rates are all centered near 0. Multiband delays fall within an ambiguity search window of (−8.53 ns, 8.53 ns) as they are derived from measurements spaced at ALMA's channel separation of 58.592375 MHz (Matthews et al. 2018 ; Event Horizon Telescope Collaboration et al. 2019d ).

Figure 4.  870 μ m contours of incoherently averaged fringe power in 5% increments vs. delay and rate for a single scan on J0423−0120 for the ALMA–SMA baseline (October 21, 09:38 UTC). Other detections reported in Table 1 also exhibit clear peaks vs. delay/rate.

The fringe detection threshold was conservatively set at S/N > 7 to prevent false detections, and all resulting detections are summarized in Table 1 ordered by target source. The maximum spatial frequencies sampled are greater than 10.9 G λ between ALMA and the SMA, which significantly exceeds the largest spatial frequencies sampled by the EHT for M87* at 1.3 mm on the longest baseline between Hawaii and Europe (approximately 8 G λ ). The highest-S/N detections exceed 70. Simultaneous detections in all four polarization products were achieved on the ALMA–SMA baseline for J0423−0120 . The zero-baseline flux densities at 870 μ m were obtained from the ALMA local interferometry (Crew et al. 2023 ). The flux densities were 1.4, 1.0, 2.4, 1.2, and 4.9 Jy on CTA 102, BL Lac, J0423−0120 , J0510+1800 , and J0522−3627 , respectively. The source structure of the targets in this work is not known a priori, so it is not possible to say with precision how the correlated amplitudes should vary as a function of baseline length. Furthermore, these observations were designed to be a detection experiment and not carried out with all procedures that would allow robust VLBI flux density calibration. Nevertheless, the S/N on the ALMA–APEX baselines appears to be anomalously low given the short baseline length, which would ordinarily be sensitive to both small-scale structure (10–100 μ as) and larger-scale structure (10–100 mas). This is likely attributable to phase instabilities suspected in the APEX receiver (see Section 2.2.2 ), which has since been retired. Follow-on experiments, already scheduled, will focus on calibration and robust flux density measurements versus baseline length.

Table 1.  870 μ m Detections on the Indicated Baselines, Sources, and Polarizations

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HOPS reports two coherence times: one corresponding to the point below which there is only a small amount of coherence loss within the uncertainty of amplitudes and another corresponding to the maximum S/N. For most of the scans in Table 1 , we report the former. In a few low-S/N cases where the routine was unable to fit the coherence, the coherence time based on S/N is reported instead. The coherence times across baselines range from approximately 10 to 30 s for most cases. For BL Lac, the longer coherence times may be an artifact of the moderate S/N.

3.2. 1.3 mm (230 GHz) Comparison

Presently, the EHT observes at 1.3 mm (Event Horizon Telescope Collaboration et al. 2019b ). Figure 5 compares the Fourier components of the 870 μ m detections on various sources to the 1.3 mm coverage of the 2017 EHT array on M87* (Event Horizon Telescope Collaboration et al. 2019d ). The 870 μ m detections on ALMA–IRAM30m and ALMA–SMA baselines have a higher nominal angular resolution (19 μ as) than the highest-resolution M87* detections (nominally 25 μ as).

Figure 5.  Detections on various targets at 345 GHz (see Table 1 ). The u – v locations of 230 GHz detections on M87* during the EHT 2017 April campaign are shown in gray including low-S/N scans at (25 μ as) −1 .

For a source-specific comparison of the 1.3 mm and 870 μ m bands, ALMA and IRAM30m observed BL Lac at 1.3 mm during three scans at the end of the eastern subarray scheduling block of the 2018 October session. Those data were searched using the same HOPS incoherent averaging method as was used for the 870 μ m observations and provide an independent application of the approach. The 1.3 mm scans provide a check of the 870 μ m processing and a point of comparison for the 870 μ m detections.

The amplitude and S/N values for one of the 1.3 mm scans are plotted in Figure 6 versus the duration of incoherently averaged segments. The S/N values are approximately tenfold greater at 1.3 mm than at 870 μ m (see Figure 3 ), which likely results from a combination of factors that boost sensitivity at the longer wavelength: lower opacity, lower receiver noise, greater aperture efficiency, a wider beam, greater coherence, and greater source flux density. The coherence time determined using HOPS was comparable for the three scans to what was found at 870 μ m: on the order of 6–30 s. As with the 870 μ m measurements, the S/N values asymptote as the segment duration decreases below the coherence time. The consistency of the S/N trends in the 870 μ m and 1.3 mm scans suggests that the behavior is a real feature of the data and not an artifact of the analysis.

Figure 6.  1.3 mm amplitude (open blue circles, left axes) and S/N (filled red squares, right axes) vs. the duration of coherently integrated segments, which are incoherently averaged. Each subplot shows a different polarization on the baseline between ALMA and IRAM30m for a single scan on BL Lac on October 19, 01:13 UTC. Other BL Lac detections listed in Table 2 have a similar dependence on segment duration. The noise-debiased amplitude and coherence time were derived using HOPS and are indicated by the horizontal blue dashed line and the vertical solid black line, respectively. These data were calibrated in the same manner as the 870 μ m detections.

Fringe power contours at 1.3 mm are plotted as a function of multiband delay and rate in Figure 7 , exhibiting obvious peaks. The delays for each of the four polarization cross products is consistent across scans, and the 1.3 mm fringes are summarized in Table 2 . All four polarization cross-hands are detected in each of the three 1.3 mm scans. The 6.4 G λ spatial frequencies are 50% smaller than the 870 μ m scans on the AP baseline, which corresponds to the frequency scaling between the two bands. The 1.3 mm zero-baseline flux density of BL Lac deduced from the ALMA local interferometry (Crew et al. 2023 ) was 1.2 Jy.

Figure 7.  1.3 mm contours of incoherently averaged fringe power in 5% increments vs. delay and rate for the baseline between ALMA and IRAM30m. This example is for a single scan on BL Lac taken on October 19, 01:13 UTC. Other detections reported in Table 2 also exhibit clear peaks vs. in delay-delay rate search space.

Table 2.  1.3 mm Detections on the ALMA–IRAM30m Baseline toward BL Lac for Indicated Polarizations

Note. Scans listed top to bottom on October 19 begin at 01:03, 01:09, and 01:13 UTC.

3.3. Coherence and Allan Deviation

It is convenient to characterize the phase noise of an interferometer by its Allan deviation, which is a measure of fractional stability for an oscillator, time standard, or any time-variable process. When computing the Allan deviation of an observed VLBI interferometer phase, one normalizes by the frequency of observation to produce a dimensionless quantity. The relationships of Allan deviation to the statistical variance, coherence, and phase power spectrum can be found in Thompson et al. ( 2017 ). Examples of the Allan deviation of VLBI systems referenced to hydrogen maser time standards and operating at 1.3 cm and 3 mm wavelengths can be found in Rogers & Moran ( 1981 ) and Rogers et al. ( 1984 ), respectively, and show that at short wavelengths, decoherence is a potential concern. Alternatives to hydrogen masers for short-wavelength VLBI work have been explored (e.g., Doeleman et al. 2011 ). In this section, we compare the observed Allan deviation of the VLBI interferometric phase to limiting factors including the stability of time and frequency standards used in the experiment as well as instabilities due to atmospheric turbulence.

Figure 8 shows the Allan deviation for 870 μ m scans on the ALMA–SMA baseline. Over most integration times, the 870 μ m Allan deviation is comparable to but greater than the maser–maser reference. The 870 μ m traces exhibit relatively small scan-to-scan variation during the course of the brief fringe test when conditions were relatively stable. For comparison, Figure 8 also shows the Allan deviations for a large number of high-S/N 1.3 mm scans from the 2017 EHT campaign (Event Horizon Telescope Collaboration et al. 2019d ). At times of less than about 5 s, the red 1.3 mm traces all approach the limit set by the maser references. At times longer than 5 s, the red traces are noticeably scattered. The scatter exists because of the variability of atmospheric conditions during the course of an observing campaign.

Figure 8.  Allan deviation for 870 μ m (345 GHz) scans observed on the ALMA–SMA baseline (blue lines). For comparison, red lines show the Allan deviation for high-S/N scans (nominally 5 minutes long) during the 1.3 mm (230 GHz) 2017 EHT campaign (Event Horizon Telescope Collaboration et al. 2019b ). Weather variability during the 2017 campaign is responsible for the spread in those scans. The means of the individual Allan deviation traces are shown in bold for the two frequencies. The 870 μ m and 1.3 mm mean traces approach the nominal Allan deviation for a pair of T4 Science brand iMaser 3000 model masers (Thompson et al. 2017 ) at short timescales. At intermediate timescales, atmospheric turbulence can become important. The Allan deviation associated with Kolmogorov turbulence is plotted for a set of nominal parameters (Treuhaft & Lanyi 1987 ).

The tropospheric delay is essentially independent of wavelength for wavelengths longer than about 600 μ m as described by the Smith–Weintraub equation (see Thompson et al. 2017 , Chapter 13). Thus, the Allan deviation is expected to be independent of wavelength for our observations. When the atmospheric conditions are stable, the 1.3 mm Allan deviation for individual scans approaches the maser–maser limit across all integration times. The mean of the 1.3 mm scans is within a factor of approximately 2 of the mean of the 870 μ m traces. The 870 μ m mean Allan deviation on the plot happens to be lower than the 1.3 mm mean for most integration times. However, we do not consider this difference to be significant given the extremely small 870 μ m data set. Further, the observations in 2017 April and 2018 October were of course made in differing weather conditions.

To assess the impact of atmospheric turbulence at longer times, the Allan deviation associated with atmospheric Kolmogorov turbulence is plotted for a set of nominal conditions following the approach outlined by Treuhaft & Lanyi ( 1987 ): 10 m s −1 wind speed, 2 km troposphere scale height, 1.99 × 10 −7 m −1/3 Kolmogorov coefficient, and independent distant sites. The nominal Kolmogorov trace exceeds the maser–maser Allan deviation at longer times, where we expect atmospheric effects to dominate. Beyond 10 s, the nominal Kolmogorov trace matches the shape of the 1.3 mm mean. Although the 870 μ m mean falls somewhere between the maser–maser and nominal Kolmogorov limits, the atmospheric contribution may become more apparent in the future with scans spanning more variable weather conditions.

3.4. Phasing Efficiency

An important figure of merit when used to monitor the performance of phased array beamformers is phasing efficiency. This is a measure of how effectively outputs of the dishes in the local array are coherently summed to synthesize a single IF output from the array's aggregated collecting area. For each array site, periodic estimates of phasing efficiency over time are stored with other essential metadata for use in calibration.

The ALMA and SMA phased arrays experienced lower and more variable phasing efficiency during the 870 μ m test than is typical for 1.3 mm observing in similar conditions. At 870 μ m, atmospheric opacity is between 3 and 3.5 times that for 1.3 mm given the same precipitable water vapor. Further source fluxes decline with increasing frequency or shorter wavelength. Both of these factors result in a lower local array fringe S/N. There is thus greater error in the fits of the antenna phase corrections. Tuning within the band avoids the deep absorption lines due to atmospheric water resonances at 325 and 385 GHz, which would reduce the S/N still further. Also, the atmospheric phase fluctuations tracked by the adaptive phased array system have a greater amplitude for observations in the higher-frequency band. Crew et al. ( 2023 ) note that that moist, windy conditions tend to diminish phasing efficiency, and the winds were quite high at ALMA during the test. At dry, less windy times, ALMA obtained higher phasing efficiencies approaching 100%. While NOEMA participated in this test with a single dish, not as a phased array, all of these factors are expected to apply as well to NOEMA, which is now equipped with a phased array backend capable of beamforming in both the 1.3 mm and 870 μ m bands.

Water vapor radiometer (WVR) based phasing corrections were not in use during the 2018 test. Independent testing at ALMA shows that fast WVR corrections are effective at improving the efficiency when phase fluctuations are primarily due to water vapor. Phasing control loop algorithms are constantly being improved and in future will be better tuned to the 870 μ m wave band. These improvements will expand the opportunities for 870 μ m observing in a wider range of weather conditions and on weaker sources. Despite these challenges, VLBI detections at 870 μ m can be readily achieved even when phasing efficiencies are relatively low and in nonideal weather conditions.

4. Future Directions

Achieving 870 μ m VLBI fringes has strong implications for science directions that future global arrays operating at this wavelength can explore. As angular resolution scales with wavelength, we anticipate improving resolution from ∼23 to ∼15 μ as on the longest EHT baselines (Figure 5 ). Plasma propagation processes typically scale as wavelength squared, so at 870 μ m, scatter broadening of Sgr A* reduces to ∼5 μ as, further sharpening resolution and increasing signal-to-noise on the longest VLBI baselines. Similarly, Faraday rotation measured across the bandpass of EHT receivers at 870 μ m can be used to improve estimates of accretion plasma densities and magnetic field geometries close to EHT targets. For both Sgr A* and M87*, the images at 870 μ m and 1.3 mm are determined predominantly by the achromatic gravitational lensing and hence should exhibit similar characteristics, implying that the aggregate Fourier coverage of VLBI observations at different frequencies can be used to improve modeling of the gravitationally lensed emission and the imaging fidelity generally (Chael et al. 2023 ). Figure 9 shows Fourier amplitudes as a function of radius for GRMHD 156 models of M87* and Sgr A*. Inclusion of 345 GHz observations adds coverage in the visibility plane regions not sampled at 230 GHz, and it extends baseline lengths for higher angular resolution as well as enhanced overall sampling of Fourier spatial frequencies to allow dynamical reconstructions of accretion and jet launch close to the event horizon.

Figure 9.  Left: visibility amplitudes for simulated observations of M87* (top) and Sgr A* (bottom) at observing wavelengths of 1.3 mm (gray) and 0.87 mm (red). The synthetic data have been generated using the ngehtsim package assuming array specifications appropriate for the phase 2 ngEHT array from Doeleman et al. ( 2023 ), including simultaneous dual-band observations, the use of the FPT calibration technique, and 16 GHz of bandwidth at both frequencies. Data points are colored by their S/N on an integration time of 5 minutes, and data points with S/N < 3 have been flagged. Right: images produced from GRMHD simulations of the M87* (top two panels; Event Horizon Telescope Collaboration et al. 2019e ) and Sgr A* (bottom two panels; Event Horizon Telescope Collaboration et al. 2022b ) accretion flows, used to generate the synthetic data shown in the left panels. Both simulations have been ray-traced at observing wavelengths of 1.3 mm (gray) and 0.87 mm (red), and the frequency-dependent effects of interstellar scattering have been applied to the Sgr A* images (Johnson 2016 ; Johnson et al. 2018 ).

5. Conclusions

VLBI fringe detections on baselines between ALMA–APEX, ALMA–IRAM30m, and ALMA–SMA have been achieved at 870 μ m for multiple AGN sources. S/Ns were between approximately 10 and 70. Despite marginal weather conditions across the array, detections to multiple stations and sources were obtained. This work demonstrates that the EHT instrumentation is viable at 870 μ m (345 GHz) and will provide a critical advance in array capability. EHT-wide observations at 870 μ m would yield a fringe spacing of about 15 μ as and, with a full track of coverage, would significantly enhance the fine details of the EHT images of AGN and horizon-scale targets (Doeleman et al. 2019 , 2023 ; Johnson et al. 2023 ).

Acknowledgments

This work was supported by the National Science Foundation (grants AST-1935980, AST-1743747, AST-1440254), an ALMA Cycle 5 North America Development Award, the Gordon and Betty Moore Foundation (awards GBMF3561, GBMF5278, and GBMF10423), and a generous gift from the Deepak Raghavan Family Foundation. Work on this project was conducted in part at the Black Hole Initiative at Harvard University (funded through grants 60477, 61479, and 62286 from the John Templeton Foundation and grant GBMF8273 from the Gordon and Betty Moore Foundation). This work is partly based on observations carried out with the IRAM 30 m telescope and the NOEMA Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). The IRAM NOEMA phasing project was supported by the European Research Council (ERC) Synergy Grant "BlackHoleCam: Imaging the Event Horizon of Black Holes" (grant 610058). The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica. The SMA gratefully acknowledges the efforts of its staff for supporting these observations, including those of the operator on duty, R. Howie. This publication is based on data acquired with the APEX. APEX is a collaboration between the Max-Planck-Institut fur Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory. This work was an activity external to JPL, and effort by A.R. was not in their capacity as an employee of the Jet Propulsion Laboratory, California Institute of Technology. The GLT is supported by the the Ministry of Science and Technology (MOST) of Taiwan (103-2119-M-001-010-MY2, 105-2119-M-001-042, 106-2119-M-001-013, 107-2119-M-001-041, 108-2112-M-001-048, 109-2124-M-001-005, 110-2124-M-001-007) and the National Science and Technology Council (NSTC) of Taiwan (111-2124-M-001-005, 112-2124-M-001-014).

The Event Horizon Telescope Collaboration additionally thanks the following organizations and programs: the Academia Sinica; the Academy of Finland (projects 274477, 284495, 312496, 315721); the Agencia Nacional de Investigación y Desarrollo (ANID), Chile via NCN19 058 (TITANs), Fondecyt 1221421 and BASAL FB210003; the Alexander von Humboldt Stiftung; an Alfred P. Sloan Research Fellowship; Allegro, the European ALMA Regional Centre node in the Netherlands, the NL astronomy research network NOVA, and the astronomy institutes of the University of Amsterdam, Leiden University, and Radboud University; the ALMA North America Development Fund; the Astrophysics and High Energy Physics program by MCIN (with funding from European Union NextGenerationEU, PRTR-C17I1); the Brinson Foundation; "la Caixa" Foundation (ID 100010434) through fellowship codes LCF/BQ/DI22/11940027 and LCF/BQ/DI22/11940030; Chandra DD7-18089X and TM6-17006X; the China Scholarship Council; the China Postdoctoral Science Foundation fellowships (2020M671266, 2022M712084); Consejo Nacional de Humanidades, Ciencia y Tecnología (CONAHCYT, Mexico, projects U0004-246083, U0004-259839, F0003-272050, M0037-279006, F0003-281692, 104497, 275201, 263356); the Colfuturo Scholarship; the Consejería de Economía, Conocimiento, Empresas y Universidad of the Junta de Andalucía (grant P18-FR-1769); the Consejo Superior de Investigaciones Científicas (grant 2019AEP112); the Delaney Family via the Delaney Family John A. Wheeler Chair at Perimeter Institute; Dirección General de Asuntos del Personal Académico-Universidad Nacional Autónoma de México (DGAPA-UNAM, projects IN112820 and IN108324); the Dutch Research Council (NWO) for the VICI award (grant 639.043.513), the grant OCENW.KLEIN.113, and the Dutch Black Hole Consortium (with project No. NWA 1292.19.202) of the research program the National Science Agenda; the Dutch National Supercomputers, Cartesius and Snellius (NWO grant 2021.013); the EACOA Fellowship awarded by the East Asia Core Observatories Association, which consists of the Academia Sinica Institute of Astronomy and Astrophysics, the National Astronomical Observatory of Japan, Center for Astronomical Mega-Science, Chinese Academy of Sciences, and the Korea Astronomy and Space Science Institute; the European Union Horizon 2020 research and innovation program under grant agreements RadioNet (No. 730562), M2FINDERS (No. 101018682), and FunFiCO (No. 777740); the European Research Council for the advanced grant "JETSET: Launching, propagation and emission of relativistic jets from binary mergers and across mass scales" (grant No. 884631); the European Horizon Europe staff exchange (SE) program HORIZON-MSCA-2021-SE-01 grant NewFunFiCO (No. 10108625); the Horizon ERC Grants 2021 program under grant agreement No. 101040021; the FAPESP (Fundação de Amparo á Pesquisa do Estado de São Paulo) under grant 2021/01183-8; the Fondo CAS-ANID folio CAS220010; the Generalitat Valenciana (grants APOSTD/2018/177 and ASFAE/2022/018) and GenT Program (project CIDEGENT/2018/021); the Institute for Advanced Study; the Istituto Nazionale di Fisica Nucleare (INFN) sezione di Napoli, iniziative specifiche TEONGRAV; the International Max Planck Research School for Astronomy and Astrophysics at the Universities of Bonn and Cologne; DFG research grant "Jet physics on horizon scales and beyond" (grant No. 443220636); Joint Columbia/Flatiron Postdoctoral Fellowship (research at the Flatiron Institute is supported by the Simons Foundation); the Japan Ministry of Education, Culture, Sports, Science and Technology (MEXT; grant JPMXP1020200109); the Japan Society for the Promotion of Science (JSPS) Grant-in-Aid for JSPS Research Fellowship (JP17J08829); the Joint Institute for Computational Fundamental Science, Japan; the Key Research Program of Frontier Sciences, Chinese Academy of Sciences (CAS; grants QYZDJ-SSW-SLH057, QYZDJSSW-SYS008, ZDBS-LY-SLH011); the Leverhulme Trust Early Career Research Fellowship; the Max-Planck-Gesellschaft (MPG); the Max Planck Partner Group of the MPG and the CAS; the MEXT/JSPS KAKENHI (grants 18KK0090, JP21H01137, JP18H03721, JP18K13594, 18K03709, JP19K14761, 18H01245, 25120007, 19H01943, 21H01137, 21H04488, 22H00157, 23K03453); the MICINN Research Projects PID2019-108995GB-C22, PID2022-140888NB-C22; the MIT International Science and Technology Initiatives (MISTI) Funds; the Ministry of Science and Technology (MOST) of Taiwan (105-2112-M-001-025-MY3, 106-2112-M-001-011, 106-2119-M-001-027, 106-2923-M-001-005, 107-2119-M-001-017, 107-2119-M-001-020, 107-2119-M-110-005, 107-2923-M-001-009, 108-2112-M-001-051, 108-2923-M-001-002, 109-2112-M-001-025, 109-2923-M-001-001, 110-2112-M-001-033, 110-2923-M-001-001, and 112-2112-M-003-010-MY3); the Ministry of Education (MoE) of Taiwan Yushan Young Scholar Program; the Physics Division, National Center for Theoretical Sciences of Taiwan; the National Aeronautics and Space Administration (NASA; Fermi Guest Investigator grant 80NSSC23K1508, NASA Astrophysics Theory Program grant 80NSSC20K0527, NASA NuSTAR award 80NSSC20K0645); NASA Hubble Fellowship grants HST-HF2-51431.001-A and HST-HF2-51482.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555; the National Institute of Natural Sciences (NINS) of Japan; the National Key Research and Development Program of China (grants 2016YFA0400704, 2017YFA0402703, 2016YFA0400702); the National Science and Technology Council (NSTC; grants NSTC 111-2112-M-001-041, NSTC 111-2124-M-001-005, NSTC 112-2124-M-001-014); the US National Science Foundation (NSF; grants AST-0096454, AST-0352953, AST-0521233, AST-0705062, AST-0905844, AST-0922984, AST-1126433, OIA-1126433, AST-1140030, DGE-1144085, AST-1207704, AST-1207730, AST-1207752, MRI-1228509, OPP-1248097, AST-1310896, AST-1555365, AST-1614868, AST-1615796, AST-1715061, AST-1716327, AST-1726637, OISE-1743747, AST-1816420, AST-1952099, AST-2034306, AST-2205908, AST-2307887); NSF Astronomy and Astrophysics Postdoctoral Fellowship (AST-1903847); the Natural Science Foundation of China (grants 11650110427, 10625314, 11721303, 11725312, 11873028, 11933007, 11991052, 11991053, 12192220, 12192223, 12273022, 12325302, 12303021); the Natural Sciences and Engineering Research Council of Canada (NSERC; including a Discovery Grant and the NSERC Alexander Graham Bell Canada Graduate Scholarships-Doctoral Program); the National Research Foundation of Korea (the Global PhD Fellowship Grant: grants NRF-2015H1A2A1033752, the Korea Research Fellowship Program: NRF-2015H1D3A1066561, Brain Pool Program: 2019H1D3A1A01102564, Basic Research Support grant 2019R1F1A1059721, 2021R1A6A3A01086420, 2022R1C1C1005255, 2022R1F1A1075115); Netherlands Research School for Astronomy (NOVA) Virtual Institute of Accretion (VIA) postdoctoral fellowships; NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation; Onsala Space Observatory (OSO) national infrastructure for the provisioning of its facilities/observational support (OSO receives funding through the Swedish Research Council under grant 2017–00648); the Perimeter Institute for Theoretical Physics (research at Perimeter Institute is supported by the Government of Canada through the Department of Innovation, Science and Economic Development and by the Province of Ontario through the Ministry of Research, Innovation and Science); the Portuguese Foundation for Science and Technology (FCT) grants (Individual CEEC program—5th edition, https://doi.org/10.54499/UIDP/04106/2020 , PTDC/FIS-AST/3041/2020, CERN/FIS-PAR/0024/2021, 2022.04560.PTDC); the Princeton Gravity Initiative; the Spanish Ministerio de Ciencia e Innovación (grants PGC2018-098915-B-C21, AYA2016-80889-P, PID2019-108995GB-C21, PID2020-117404GB-C21); the University of Pretoria for financial aid in the provision of the new Cluster Server nodes and SuperMicro (USA) for a SEEDING GRANT approved toward these nodes in 2020; the Shanghai Municipality orientation program of basic research for international scientists (grant No. 22JC1410600); the Shanghai Pilot Program for Basic Research, Chinese Academy of Science, Shanghai Branch (JCYJ-SHFY-2021-013); the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award for the Instituto de Astrofísica de Andalucía (SEV-2017–0709); the Spanish Ministry for Science and Innovation grant CEX2021-001131-S funded by MCIN/AEI/10.13039/501100011033; the Spinoza Prize SPI 78–409; the South African Research Chairs Initiative through the South African Radio Astronomy Observatory (SARAO; grant ID 77948), which is a facility of the National Research Foundation (NRF), an agency of the Department of Science and Innovation (DSI) of South Africa; the Swedish Research Council (VR); the Taplin Fellowship; the Toray Science Foundation; the UK Science and Technology Facilities Council (grant no. ST/X508329/1); the US Department of Energy (USDOE) through the Los Alamos National Laboratory (operated by Triad National Security, LLC, for the National Nuclear Security Administration of the USDOE, contract 89233218CNA000001); and the YCAA Prize Postdoctoral Fellowship.

We thank the staff at the participating observatories, correlation centers, and institutions for their enthusiastic support. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2016.1.01154.V, ADS/JAO.ALMA#2011.0.00010.E, and ADS/JAO.ALMA#2011.0.00012.E. See https://almascience.nrao.edu/alma-data/eht-2018 for more detail and access to the data. ALMA is a partnership of the European Southern Observatory (ESO; Europe, representing its member states), NSF, and National Institutes of Natural Sciences of Japan, together with National Research Council (Canada), Ministry of Science and Technology (MOST; Taiwan), Academia Sinica Institute of Astronomy and Astrophysics (ASIAA; Taiwan), and Korea Astronomy and Space Science Institute (KASI; Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, Associated Universities, Inc. (AUI)/NRAO, and the National Astronomical Observatory of Japan (NAOJ). The NRAO is a facility of the NSF operated under cooperative agreement by AUI. This research used resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under contract No. DE-AC05-00OR22725; the ASTROVIVES FEDER infrastructure, with project code IDIFEDER-2021-086; and the computing cluster of the Shanghai VLBI correlator supported by the Special Fund for Astronomy from the Ministry of Finance in China. We also thank the Center for Computational Astrophysics, National Astronomical Observatory of Japan. This work was supported by FAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo) under grant 2021/01183-8.

The EHTC has received generous donations of FPGA chips from Xilinx Inc. under the Xilinx University Program. The EHTC has benefited from technology shared under open-source license by the Collaboration for Astronomy Signal Processing and Electronics Research (CASPER). The EHT project is grateful to T4Science and Microsemi for their assistance with hydrogen masers. This research has made use of NASA's Astrophysics Data System. We gratefully acknowledge the support provided by the extended staff of the ALMA, from the inception of the ALMA Phasing Project through the observational campaigns of 2017 and 2018. We would like to thank A. Deller and W. Brisken for EHT-specific support with the use of DiFX. We acknowledge the significance that Maunakea, where the SMA EHT station is located, has for the indigenous Hawaiian people.

See, for example, Janssen et al. ( 2019 ) or the ALMA Cycle 8 2021 Technical Handbook.

NOEMA is also equipped with the phased array, though it was not commissioned at the time of this observation.

ALMA and SMA used slightly different frequency setups to match the sky frequency of the other stations; see Sections 2.2.1 and 2.2.6 .

https://www.haystack.mit.edu/tech/vlbi/hops.html

General relativistic magnetohydrodynamic.