doi.eso.org

• Goddi, Ciriaco [Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, Nijmegen, the Netherlands; Leiden Observatory—Allegro, Leiden University, Leiden, the Netherlands]
• Crew, Geoff [Massachusetts Institute of Technology Haystack Observatory, Westford, USA]
• Impellizzeri, Violette [Joint ALMA Observatory, Vitacura, Santiago de Chile, Chile]
• Martí-Vidal, Iván [Onsala Space Observatory, Chalmers University of Technology, Sweden; Department of Astronomy and Astrophysics/Astronomical Observatory, University of Valencia, Spain]
• Matthews, Lynn D. [Massachusetts Institute of Technology Haystack Observatory, Westford, USA]
• Messias, Hugo [Joint ALMA Observatory, Vitacura, Santiago de Chile, Chile]
• Rottmann, Helge [Max-Planck-Institut für Radioastronomie (MPIfR), Bonn, Germany]
• Alef, Walter [Max-Planck-Institut für Radioastronomie (MPIfR), Bonn, Germany]
• Blackburn, Lindy [Center for Astrophysics | Harvard & Smithsonian, Cambridge, USA]
• Bronzwaer, Thomas [Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, Nijmegen, the Netherlands]
• Chan, Chi-Kwan [Steward Observatory and Department of Astronomy, University of Arizona Tucson, USA]
• Davelaar, Jordy [Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, Nijmegen, the Netherlands]
• Deane, Roger [Centre for Radio Astronomy Techniques and Technologies, Department of Physics and Electronics, Rhodes University, Grahamstown, South Africa]
• Dexter, Jason [Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany]
• Doeleman, Shep [Center for Astrophysics | Harvard & Smithsonian, Cambridge, USA]
• Falcke, Heino [Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, Nijmegen, the Netherlands]
• Fish, Vincent L. [Massachusetts Institute of Technology Haystack Observatory, Westford, USA]
• Fraga-Encinas, Raquel [Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, Nijmegen, the Netherlands]
• Fromm, Christian M. [Institut für Theoretische Physik, Goethe Universität, Frankfurt am Main, Germany]
• Herrero-Illana, Ruben [European Southern Observatory (ESO)]
• Issaoun, Sara [Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, Nijmegen, the Netherlands]
• James, David [Center for Astrophysics | Harvard & Smithsonian, Cambridge, USA]
• Janssen, Michael [Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, Nijmegen, the Netherlands]
• Kramer, Michael [Max-Planck-Institut für Radioastronomie (MPIfR), Bonn, Germany]
• Krichbaum, Thomas P. [Max-Planck-Institut für Radioastronomie (MPIfR), Bonn, Germany]
• De Laurentis, Mariafelicia [Dipartimento di Fisica “E. Pancini,” Universitá di Napoli “Federico II”, Naples, Italy; INFN Sez. di Napoli, Compl. Univ. di Monte S. Angelo, Naples, Italy]
• Liuzzo, Elisabetta [INAF–Istituto di Radioastronomia, Bologna, Italy]
• Mizuno, Yosuke [Institut für Theoretische Physik, Goethe Universität, Frankfurt am Main, Germany]
• Moscibrodzka, Monika [Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, Nijmegen, the Netherlands]
• Natarajan, Iniyan [Centre for Radio Astronomy Techniques and Technologies, Department of Physics and Electronics, Rhodes University, Grahamstown, South Africa]
• Porth, Oliver [Anton Pannekoek Institute for Astronomy, University of Amsterdam, the Netherlands]
• Rezzolla, Luciano [Institut für Theoretische Physik, Goethe Universität, Frankfurt am Main, Germany]
• Rygl, Kazi [INAF–Istituto di Radioastronomia, Bologna, Italy]
• Roelofs, Freek [Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, Nijmegen, the Netherlands]
• Ros, Eduardo [Max-Planck-Institut für Radioastronomie (MPIfR), Bonn, Germany]
• Roy, Alan L. [Max-Planck-Institut für Radioastronomie (MPIfR), Bonn, Germany]
• Shao, Lijing [Max-Planck-Institut für Radioastronomie (MPIfR), Bonn, Germany; Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing, China]
• van Langevelde, Huib Jan [Leiden Observatory—Allegro, Leiden University, Leiden, the Netherlands; Joint Institute for VLBI ERIC (JIVE), Dwingeloo, the Netherlands]
• van Bemmel, Ilse [Joint Institute for VLBI ERIC (JIVE), Dwingeloo, the Netherlands]
• Tilanus, Remo [Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University, Nijmegen, the Netherlands; Leiden Observatory—Allegro, Leiden University, Leiden, the Netherlands]
• Torne, Pablo [Max-Planck-Institut für Radioastronomie (MPIfR), Bonn, Germany; Instituto de Radioastronomía Milimétrica, IRAM, Granada, Spain]
• Wielgus, Maciek [Center for Astrophysics | Harvard & Smithsonian, Cambridge, USA]
• Younsi, Ziri [Institut für Theoretische Physik, Goethe Universität, Frankfurt am Main, Germany; Mullard Space Science Laboratory, University College London, Dorking, UK]
• Zensus, J. Anton [Max-Planck-Institut für Radioastronomie (MPIfR), Bonn, Germany]
• The Event Horizon Telescope collaboration

In April 2019, the Event Horizon Telescope (EHT) collaboration revealed the first image of the candidate super- massive black hole (SMBH) at the centre of the giant elliptical galaxy Messier 87 (M87). This event-horizon-scale image shows a ring of glowing plasma with a dark patch at the centre, which is interpreted as the shadow of the black hole. This breakthrough result, which represents a powerful confirmation of Einstein’s theory of gravity, or general relativity, was made possible by assembling a global network of radio telescopes operating at millimetre wavelengths that for the first time included the Atacama Large Millimeter/submillimeter Array (ALMA). The addition of ALMA as an anchor station has enabled a giant leap forward by increasing the sensitivity limits of the EHT by an order of magnitude, effectively turning it into an imaging array. The published image demonstrates that it is now possible to directly study the event horizon shadows of SMBHs via electromagnetic radiation, thereby transforming this elusive frontier from a mathematical concept into an astrophysical reality. The expansion of the array over the next few years will include new stations on different continents — and eventually satellites in space. This will provide progressively sharper and higher-fidelity images of SMBH candidates, and potentially even movies of the hot plasma orbiting around SMBHs. These improvements will shed light on the processes of black hole accretion and jet formation on event-horizon scales, thereby enabling more precise tests of general relativity in the truly strong field regime.