The persistent shadow of the supermassive black hole of M 87

I. Observations, calibration, imaging, and analysis^⋆

¹ Massachusetts Institute of Technology Haystack Observatory, 99 Millstone Road, Westford, MA, 01886, USA
² National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
³ Black Hole Initiative at Harvard University, 20 Garden Street, Cambridge, MA 02138, USA
⁴ Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁵ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁶ Department of Physics, Faculty of Science, Universiti Malaya, 50603 Kuala Lumpur, Malaysia
⁷ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
⁸ Department of Physics & Astronomy, The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, USA
⁹ Institute of Astronomy and Astrophysics, Academia Sinica, 11F of Astronomy-Mathematics Building, AS/NTU No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan ROC
¹⁰ Departament d’Astronomia i Astrofísica, Universitat de València, C. Dr. Moliner 50, 46100 Burjassot, València, Spain
¹¹ Observatori Astronòmic, Universitat de València, C. Catedrático José Beltrán 2, 46980 Paterna, València, Spain
¹² Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
¹³ Steward Observatory and Department of Astronomy, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721, USA
¹⁴ Yale Center for Astronomy & Astrophysics, Yale University, 52 Hillhouse Avenue, New Haven, CT 06511, USA
¹⁵ Astronomy Department, Universidad de Concepción, Casilla 160, Concepción, Chile
¹⁶ Department of Physics, University of Illinois, 1110 West Green Street, Urbana, IL 61801, USA
¹⁷ Fermi National Accelerator Laboratory, MS209, PO Box 500, Batavia, IL 60510, USA
¹⁸ Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA
¹⁹ East Asian Observatory, 660 N. A’ohoku Place, Hilo, HI 96720, USA
²⁰ James Clerk Maxwell Telescope (JCMT), 660 N. A’ohoku Place, Hilo, HI 96720, USA
²¹ California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA
²² Institute of Astronomy and Astrophysics, Academia Sinica, 645 N. A’ohoku Place, Hilo, HI 96720, USA
²³ Department of Physics and Astronomy, University of Hawaii at Manoa, 2505 Correa Road, Honolulu, HI 96822, USA
²⁴ Department of Physics, McGill University, 3600 Rue University, Montréal, QC H3A 2T8, Canada
²⁵ Trottier Space Institute at McGill, 3550 Rue University, Montréal, QC H3A 2A7, Canada
²⁶ Institut de Radioastronomie Millimétrique (IRAM), 300 Rue de la Piscine, 38406 Saint-Martin-d’Hères, France
²⁷ Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo, ON N2L 2Y5, Canada
²⁸ Department of Physics and Astronomy, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada
²⁹ Waterloo Centre for Astrophysics, University of Waterloo, Waterloo, ON N2L 3G1, Canada
³⁰ Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, PO Box 9010, 6500 GL Nijmegen, The Netherlands
³¹ Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA
³² Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA
³³ Department of Physics, University of Chicago, 5720 South Ellis Avenue, Chicago, IL 60637, USA
³⁴ Enrico Fermi Institute, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA
³⁵ Princeton Gravity Initiative, Jadwin Hall, Princeton University, Princeton, NJ 08544, USA
³⁶ Data Science Institute, University of Arizona, 1230 N. Cherry Ave., Tucson, AZ 85721, USA
³⁷ Program in Applied Mathematics, University of Arizona, 617 N. Santa Rita, Tucson, AZ 85721, USA
³⁸ Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, NY 14853, USA
³⁹ Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, PR China
⁴⁰ Key Laboratory of Radio Astronomy and Technology, Chinese Academy of Sciences, A20 Datun Road, Chaoyang District, Beijing 100101, PR China
⁴¹ Korea Astronomy and Space Science Institute, Daedeok-daero 776, Yuseong-gu, Daejeon 34055, Republic of Korea
⁴² Department of Astronomy, Yonsei University, Yonsei-ro 50, Seodaemun-gu 03722 Seoul, Republic of Korea
⁴³ Physics Department, Fairfield University, 1073 North Benson Road, Fairfield, CT 06824, USA
⁴⁴ Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801, USA
⁴⁵ Instituto de Astronomía, Universidad Nacional Autónoma de México (UNAM), Apdo Postal 70-264, Ciudad de México, Mexico
⁴⁶ Institut für Theoretische Physik, Goethe-Universität Frankfurt, Max-von-Laue-Straße 1, 60438 Frankfurt am Main, Germany
⁴⁷ Research Center for Intelligent Computing Platforms, Zhejiang Laboratory, Hangzhou 311100, PR China
⁴⁸ Tsung-Dao Lee Institute, Shanghai Jiao Tong University, Shengrong Road 520, Shanghai 201210, PR China
⁴⁹ Department of Astronomy and Columbia Astrophysics Laboratory, Columbia University, 500 W. 120th Street, New York, NY 10027, USA
⁵⁰ Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Avenue, New York, NY 10010, USA
⁵¹ Dipartimento di Fisica “E. Pancini”, Università di Napoli “Federico II”, Compl. Univ. di Monte S. Angelo, Edificio G, Via Cinthia, 80126 Napoli, Italy
⁵² INFN Sez. di Napoli, Compl. Univ. di Monte S. Angelo, Edificio G, Via Cinthia, 80126 Napoli, Italy
⁵³ Wits Centre for Astrophysics, University of the Witwatersrand, 1 Jan Smuts Avenue, Braamfontein, Johannesburg 2050, South Africa
⁵⁴ Department of Physics, University of Pretoria, Hatfield, Pretoria 0028, South Africa
⁵⁵ Centre for Radio Astronomy Techniques and Technologies, Department of Physics and Electronics, Rhodes University, Makhanda 6140, South Africa
⁵⁶ ASTRON, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
⁵⁷ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 Place Jules Janssen, 92195 Meudon, France
⁵⁸ JILA and Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309, USA
⁵⁹ National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100101, PR China
⁶⁰ Las Cumbres Observatory, 6740 Cortona Drive, Suite 102, Goleta, CA 93117-5575, USA
⁶¹ Department of Physics, University of California, Santa Barbara, CA 93106-9530, USA
⁶² National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
⁶³ Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 32-D476, 77 Massachusetts Ave., Cambridge, MA 02142, USA
⁶⁴ Google Research, 355 Main St., Cambridge, MA 02142, USA
⁶⁵ Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Emil-Fischer-Str. 31, 97074 Würzburg, Germany
⁶⁶ Department of History of Science, Harvard University, Cambridge, MA 02138, USA
⁶⁷ Department of Physics, Harvard University, Cambridge, MA 02138, USA
⁶⁸ NCSA, University of Illinois, 1205 W. Clark St., Urbana, IL 61801, USA
⁶⁹ Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, R. do Matão, 1226, São Paulo, SP 05508-090, Brazil
⁷⁰ Dipartimento di Fisica, Università degli Studi di Cagliari, SP Monserrato-Sestu km 0.7, 09042 Monserrato, CA, Italy
⁷¹ INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius, CA, Italy
⁷² INFN, Sezione di Cagliari, 09042 Monserrato, CA, Italy
⁷³ CP3-Origins, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
⁷⁴ Instituto Nacional de Astrofísica, Óptica y Electrónica, Apartado Postal 51 y 216, 72000 Puebla Pue., Mexico
⁷⁵ Consejo Nacional de Humanidades, Ciencia y Tecnología, Av. Insurgentes Sur 1582, 03940 Ciudad de México, Mexico
⁷⁶ Key Laboratory for Research in Galaxies and Cosmology, Chinese Academy of Sciences, Shanghai 200030, PR China
⁷⁷ Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, 2-12 Hoshigaoka, Mizusawa, Oshu, Iwate 023-0861, Japan
⁷⁸ Department of Astronomical Science, The Graduate University for Advanced Studies (SOKENDAI), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁷⁹ NOVA Sub-mm Instrumentation Group, Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen, The Netherlands
⁸⁰ Department of Astronomy, School of Physics, Peking University, Beijing 100871, PR China
⁸¹ Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, PR China
⁸² Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
⁸³ The Institute of Statistical Mathematics, 10-3 Midori-cho, Tachikawa, Tokyo 190-8562, Japan
⁸⁴ Department of Statistical Science, The Graduate University for Advanced Studies (SOKENDAI), 10-3 Midori-cho, Tachikawa, Tokyo 190-8562, Japan
⁸⁵ Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8583, Japan
⁸⁶ Leiden Observatory, Leiden University, Postbus 2300, 9513 RA Leiden, The Netherlands
⁸⁷ ASTRAVEO LLC, PO Box 1668, Gloucester, MA 01931, USA
⁸⁸ Applied Materials Inc., 35 Dory Road, Gloucester, MA 01930, USA
⁸⁹ Institute for Astrophysical Research, Boston University, 725 Commonwealth Ave., Boston, MA 02215, USA
⁹⁰ University of Science and Technology, Gajeong-ro 217, Yuseong-gu, Daejeon 34113, Republic of Korea
⁹¹ Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8582, Japan
⁹² Joint Institute for VLBI ERIC (JIVE), Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
⁹³ Department of Astronomy and Atmospheric Sciences, Kyungpook National University, Daegu 702-701, Republic of Korea
⁹⁴ Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
⁹⁵ Kogakuin University of Technology & Engineering, Academic Support Center, 2665-1 Nakano, Hachioji, Tokyo 192-0015, Japan
⁹⁶ Graduate School of Science and Technology, Niigata University, 8050 Ikarashi 2-no-cho, Nishi-ku, Niigata 950-2181, Japan
⁹⁷ Physics Department, National Sun Yat-Sen University, No. 70, Lien-Hai Road, Kaosiung City 80424, Taiwan ROC
⁹⁸ School of Astronomy and Space Science, Nanjing University, Nanjing 210023, PR China
⁹⁹ Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Nanjing 210023, PR China
¹⁰⁰ INAF-Istituto di Radioastronomia, Via P. Gobetti 101, 40129 Bologna, Italy
¹⁰¹ INAF-Istituto di Radioastronomia & Italian ALMA Regional Centre, Via P. Gobetti 101, 40129 Bologna, Italy
¹⁰² Department of Physics, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan ROC
¹⁰³ Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Morelia 58089, Mexico
¹⁰⁴ Yunnan Observatories, Chinese Academy of Sciences, 650011 Kunming, Yunnan Province, PR China
¹⁰⁵ Center for Astronomical Mega-Science, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012, PR China
¹⁰⁶ Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, 650011 Kunming, PR China
¹⁰⁷ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
¹⁰⁸ Gravitation and Astroparticle Physics Amsterdam (GRAPPA) Institute, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
¹⁰⁹ Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08544, USA
¹¹⁰ School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, PR China
¹¹¹ Institut de Radioastronomie Millimétrique (IRAM), Avenida Divina Pastora 7, Local 20, 18012 Granada, Spain
¹¹² National Institute of Technology, Hachinohe College, 16-1 Uwanotai, Tamonoki, Hachinohe City, Aomori 039-1192, Japan
¹¹³ Research Center for Astronomy, Academy of Athens, Soranou Efessiou 4, 115 27 Athens, Greece
¹¹⁴ Department of Physics, Villanova University, 800 Lancaster Avenue, Villanova, PA 19085, USA
¹¹⁵ Physics Department, Washington University, CB 1105, St. Louis, MO 63130, USA
¹¹⁶ School of Physics, Georgia Institute of Technology, 837 State St NW, Atlanta, GA 30332, USA
¹¹⁷ Department of Astronomy and Space Science, Kyung Hee University, 1732, Deogyeong-daero, Giheung-gu, Yongin-si, Gyeonggi-do 17104, Republic of Korea
¹¹⁸ Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8, Canada
¹¹⁹ Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada
¹²⁰ Canadian Institute for Advanced Research, 180 Dundas St West, Toronto, ON M5G 1Z8, Canada
¹²¹ Department of Physics, National Taiwan Normal University, No. 88, Sec. 4, Tingzhou Rd., Taipei 116, Taiwan ROC
¹²² Center of Astronomy and Gravitation, National Taiwan Normal University, No. 88, Sec. 4, Tingzhou Road, Taipei 116, Taiwan ROC
¹²³ Finnish Centre for Astronomy with ESO, University of Turku, 20014 Turku, Finland
¹²⁴ Aalto University Metsähovi Radio Observatory, Metsähovintie 114, 02540 Kylmälä, Finland
¹²⁵ Gemini Observatory/NSF’s NOIRLab, 670 N. A’ohōkū Place, Hilo, HI 96720, USA
¹²⁶ Frankfurt Institute for Advanced Studies, Ruth-Moufang-Strasse 1, 60438 Frankfurt, Germany
¹²⁷ School of Mathematics, Trinity College, Dublin 2, Ireland
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, 00076 Aalto, Finland
¹³² Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK
¹³³ National Biomedical Imaging Center, Peking University, Beijing 100871, PR China
¹³⁴ College of Future Technology, Peking University, Beijing 100871, PR 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, Alberta T1K 3M4, Canada
¹³⁷ Netherlands Organisation for Scientific Research (NWO), Postbus 93138, 2509 AC Den Haag, The Netherlands
¹³⁸ Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai 980-8578, Japan
¹³⁹ Astronomical Institute, Tohoku University, Sendai 980-8578, Japan
¹⁴⁰ Department of Physics and Astronomy, Seoul National University, Gwanak-gu, Seoul 08826, Republic of Korea
¹⁴¹ University of New Mexico, Department of Physics and Astronomy, Albuquerque, NM 87131, USA
¹⁴² Physics Department, Brandeis University, 415 South Street, Waltham, MA 02453, USA
¹⁴³ Tuorla Observatory, Department of Physics and Astronomy, University of Turku, Turku, Finland
¹⁴⁴ Radboud Excellence Fellow of Radboud University, Nijmegen, The Netherlands
¹⁴⁵ School of Natural Sciences, Institute for Advanced Study, 1 Einstein Drive, Princeton, NJ 08540, USA
¹⁴⁶ School of Physics, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China
¹⁴⁷ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
¹⁴⁸ School of Astronomy and Space Sciences, University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing 100049, PR China
¹⁴⁹ Astronomy Department, University of Science and Technology of China, Hefei 230026, PR China
¹⁵⁰ Department of Physics and Astronomy, Michigan State University, 567 Wilson Rd, East Lansing, MI 48824, USA
¹⁵¹ University of Vermont, Burlington, VT 05405, USA
¹⁵² National Chung-Shan Institute of Science and Technology, No. 566, Ln. 134, Longyuan Rd., Longtan Dist., Taoyuan City 325, Taiwan ROC
¹⁵³ Western University, 1151 Richmond Street, London, Ontario N6A 3K7, Canada
¹⁵⁴ Department of Physics, Graduate School of Science, Osaka Metropolitan University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan
¹⁵⁵ Department of Physics, National Cheng Kung University, Tainan 701401, Taiwan ROC
¹⁵⁶ Coorporación Mexicana de Investigación en Materiales S.A. de C.V. Ciencia y Tecnología 790, Colonia Saltillo 400, Saltillo, Coahuila CP 25290, Mexico
¹⁵⁷ Dipartimento di Fisica, Università di Trieste, 34127 Trieste, Italy
¹⁵⁸ INFN Sez. di Trieste, 34127 Trieste, Italy
¹⁵⁹ Ground Station for Deep Space Exploration and Telecommunication (GREAT) Project, Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan

Received: 11 September 2023
Accepted: 9 November 2023

Abstract

In April 2019, the Event Horizon Telescope (EHT) Collaboration reported the first-ever event-horizon-scale images of a black hole, resolving the central compact radio source in the giant elliptical galaxy M 87. These images reveal a ring with a southerly brightness distribution and a diameter of ∼42 μas, consistent with the predicted size and shape of a shadow produced by the gravitationally lensed emission around a supermassive black hole. These results were obtained as part of the April 2017 EHT observation campaign, using a global very long baseline interferometric radio array operating at a wavelength of 1.3 mm. Here, we present results based on the second EHT observing campaign, taking place in April 2018 with an improved array, wider frequency coverage, and increased bandwidth. In particular, the additional baselines provided by the Greenland telescope improved the coverage of the array. Multiyear EHT observations provide independent snapshots of the horizon-scale emission, allowing us to confirm the persistence, size, and shape of the black hole shadow, and constrain the intrinsic structural variability of the accretion flow. We have confirmed the presence of an asymmetric ring structure, brighter in the southwest, with a median diameter of 43.3_−3.1^+1.5 μas. The diameter of the 2018 ring is remarkably consistent with the diameter obtained from the previous 2017 observations. On the other hand, the position angle of the brightness asymmetry in 2018 is shifted by about 30° relative to 2017. The perennial persistence of the ring and its diameter robustly support the interpretation that the ring is formed by lensed emission surrounding a Kerr black hole with a mass ∼6.5 × 10⁹ M_⊙. The significant change in the ring brightness asymmetry implies a spin axis that is more consistent with the position angle of the large-scale jet.