First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole

Abstract

Abstract We present the first Event Horizon Telescope (EHT) images of M87, using observations from April 2017 at 1.3 mm wavelength. These images show a prominent ring with a diameter of ∼40 μ as, consistent with the size and shape of the lensed photon orbit encircling the “shadow” of a supermassive black hole. The ring is persistent across four observing nights and shows enhanced brightness in the south. To assess the reliability of these results, we implemented a two-stage imaging procedure. In the first stage, four teams, each blind to the others’ work, produced images of M87 using both an established method (CLEAN) and a newer technique (regularized maximum likelihood). This stage allowed us to avoid shared human bias and to assess common features among independent reconstructions. In the second stage, we reconstructed synthetic data from a large survey of imaging parameters and then compared the results with the corresponding ground truth images. This stage allowed us to select parameters objectively to use when reconstructing images of M87. Across all tests in both stages, the ring diameter and asymmetry remained stable, insensitive to the choice of imaging technique. We describe the EHT imaging procedures, the primary image features in M87, and the dependence of these features on imaging assumptions.

Keywords

Affiliated Institutions

• Goethe University Frankfurt DE
• Nederlandse Onderzoekschool Voor Astronomie
• National Sun Yat-sen University TW
• Harvard University US
• Instituto de Astrofísica de Andalucía ES
• Institute of Astronomy and Astrophysics, Academia Sinica TW
• National Radio Astronomy Observatory US
• Institut de Radioastronomie Millimétrique FR
• California Institute of Technology US
• Rhodes University ZA
• Universitat de València ES
• Netherlands Institute for Radio Astronomy NL
• National Institute of Astrophysics, Optics and Electronics MX
• University of Groningen NL
• Chalmers University of Technology SE
• Korea University of Science and Technology KR
• Fermi National Accelerator Laboratory US
• Boston University US
• Leiden University NL
• Kogakuin University JP
• University of Naples Federico II IT
• Kavli Institute for the Physics and Mathematics of the Universe JP
• University of Amsterdam NL
• Parc Científic de la Universitat de València ES
• Perimeter Institute CA
• Center for Astrophysics Harvard & Smithsonian US
• University of Illinois Urbana-Champaign US
• University of Chicago US
• University of Arizona US
• University of Waterloo CA
• Joint Institute for VLBI ERIC NL
• East Asian Observatory US
• University of Pretoria ZA
• Massachusetts Institute of Technology US
• Korea Astronomy and Space Science Institute KR
• Max Planck Institute for Radio Astronomy DE
• The Graduate University for Advanced Studies, SOKENDAI JP
• St Petersburg University RU
• Istituto Nazionale di Fisica Nucleare, Sezione di Napoli IT
• Cornell University US
• Max Planck Institute for Extraterrestrial Physics DE
• The Institute of Statistical Mathematics JP
• The University of Tokyo JP
• Woodwell Climate Research Center US
• National Astronomical Observatory of Japan JP
• Radboud University Nijmegen NL
• Google (United States) US
• Kitt Peak National Observatory US

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