The persistent shadow of the supermassive black hole of M 87
Authors:   The Event Horizon Telescope Collaboration, Akiyama Kazunori , Alberdi Antxon , Alef Walter , Algaba Juan Carlos , Anantua Richard , Asada Keiichi , Azulay Rebecca , Bach Uwe , Baczko Anne-Kathrin , Ball David , Baloković Mislav , Bandyopadhyay Bidisha , Barrett John , Bauböck Michi , Benson Bradford A. , Bintley Dan , Blackburn Lindy , Blundell Raymond , Bouman Katherine L. , Bower Geoffrey C. , Boyce Hope , Bremer Michael , Brissenden Roger , Britzen Silke , Broderick Avery E. , Broguiere Dominique , Bronzwaer Thomas , Bustamante Sandra , Carlstrom John E. , Chael Andrew , Chan Chi-kwan , Chang Dominic O. , Chatterjee Koushik , Chatterjee Shami , Chen Ming-Tang , Chen Yongjun , Cheng Xiaopeng , Cho Ilje , Christian Pierre , Conroy Nicholas S. , Conway John E. , Crawford Thomas M. , Crew Geoffrey B. , Cruz-Osorio Alejandro , Cui Yuzhu , Dahale Rohan , Davelaar Jordy , De Laurentis Mariafelicia , Deane Roger , Dempsey Jessica , Desvignes Gregory , Dexter Jason , Dhruv Vedant , Dihingia Indu K. , Doeleman Sheperd S. , Dzib Sergio A. , Eatough Ralph P. , Emami Razieh , Falcke Heino , Farah Joseph , Fish Vincent L. , Fomalont Edward , Ford H. Alyson , Foschi Marianna , Fraga-Encinas Raquel , Freeman William T. , Friberg Per , Fromm Christian M. , Fuentes Antonio , Galison Peter , Gammie Charles F. , García Roberto , Gentaz Olivier , Georgiev Boris , Goddi Ciriaco , Gold Roman , Gómez-Ruiz Arturo I. , Gómez José L. , Gu Minfeng , Gurwell Mark , Hada Kazuhiro , Haggard Daryl , Hesper Ronald , Heumann Dirk , Ho Luis C. , Ho Paul , Honma Mareki , Huang Chih-Wei L. , Huang Lei , Hughes David H. , Ikeda Shiro , Violette Impellizzeri C. M. , Inoue Makoto , Issaoun Sara , James David J. , Jannuzi Buell T. , Janssen Michael , Jeter Britton , Jiang Wu , Jiménez-Rosales Alejandra , Johnson Michael D. , Jorstad Svetlana , Jones Adam C. , Joshi Abhishek V. , Jung Taehyun , Karuppusamy Ramesh , Kawashima Tomohisa , Keating Garrett K. , Kettenis Mark , Kim Dong-Jin , Kim Jae-Young , Kim Jongsoo , Kim Junhan , Kino Motoki , Koay Jun Yi , Kocherlakota Prashant , Kofuji Yutaro , Koch Patrick M. , Koyama Shoko , Kramer Carsten , Kramer Joana A. , Kramer Michael , Krichbaum Thomas P. , Kuo Cheng-Yu , La Bella Noemi , Lee Sang-Sung , Levis Aviad , Li Zhiyuan , Lico Rocco , Lindahl Greg , Lindqvist Michael , Lisakov Mikhail , Liu Jun , Liu Kuo , Liuzzo Elisabetta , Lo Wen-Ping , Lobanov Andrei P. , Loinard Laurent , Lonsdale Colin J. , Lowitz Amy E. , Lu Ru-Sen , MacDonald Nicholas R. , Mao Jirong , Marchili Nicola , Markoff Sera , Marrone Daniel P. , Marscher Alan P. , Martí-Vidal Iván , Matsushita Satoki , Matthews Lynn D. , Medeiros Lia , Menten Karl M. , Mizuno Izumi , Mizuno Yosuke , Montgomery Joshua , Moran James M. , Moriyama Kotaro , Moscibrodzka Monika , Mulaudzi Wanga , Müller Cornelia , Müller Hendrik , Mus Alejandro , Musoke Gibwa , Myserlis Ioannis , Nagai Hiroshi , Nagar Neil M. , Nakamura Masanori , Narayanan Gopal , Natarajan Iniyan , Nathanail Antonios , Fuentes Santiago Navarro , Neilsen Joey , Ni Chunchong , Nowak Michael A. , Oh Junghwan , Okino Hiroki , Olivares Héctor , Oyama Tomoaki , Özel Feryal , Palumbo Daniel C. M. , Paraschos Georgios Filippos , Park Jongho , Parsons Harriet , Patel Nimesh , Pen Ue-Li , Pesce Dominic W. , Piétu Vincent , PopStefanija Aleksandar , Porth Oliver , Prather Ben , Psaltis Dimitrios , Pu Hung-Yi , Ramakrishnan Venkatessh , Rao Ramprasad , Rawlings Mark G. , Raymond Alexander W. , Rezzolla Luciano , Ricarte Angelo , Ripperda Bart , Roelofs Freek , Romero-Cañizales Cristina , Ros Eduardo , Roshanineshat Arash , Rottmann Helge , Roy Alan L. , Ruiz Ignacio , Ruszczyk Chet , Rygl Kazi L. J. , Sánchez Salvador , Sánchez-Argüelles David , Sánchez-Portal Miguel , Sasada Mahito , Satapathy Kaushik , Savolainen Tuomas , Schloerb F. Peter , Schonfeld Jonathan , Schuster Karl-Friedrich , Shao Lijing , Shen Zhiqiang , Small Des , Sohn Bong Won , SooHoo Jason , Salas León David Sosapanta , Souccar Kamal , Stanway Joshua S. , Sun He , Tazaki Fumie , Tetarenko Alexandra J. , Tiede Paul , Tilanus Remo P. J. , Titus Michael , Toma Kenji , Torne Pablo , Toscano Teresa , Traianou Efthalia , Trent Tyler , Trippe Sascha , Turk Matthew , van Bemmel Ilse , van Langevelde Huib Jan , van Rossum Daniel R. , Vos Jesse , Wagner Jan , Ward-Thompson Derek , Wardle John , Washington Jasmin E. , Weintroub Jonathan , Wharton Robert , Wielgus Maciek , Wiik Kaj , Witzel Gunther , Wondrak Michael F. , Wong George N. , Wu Qingwen , Yadlapalli Nitika , Yamaguchi Paul , Yfantis Aristomenis , Yoon Doosoo , Young André , Younsi Ziri , Yu Wei , Yuan Feng , Yuan Ye-Fei , Anton Zensus J. , Zhang Shuo , Zhao Guang-Yao , Zhao Shan-Shan , Allardi Alexander , Chang Shu-Hao , Chang Chih-Cheng , Chang Song-Chu , Chen Chung-Chen , Chilson Ryan , Faber Aaron , Gale David M. , Han Chih-Chiang , Han Kuo-Chang , Hasegawa Yutaka , Hernández-Rebollar José Luis , Huang Yau-De , Jiang Homin , Jinchi Hao , Kimura Kimihiro , Kubo Derek , Li Chao-Te , Lin Lupin C.-C. , Liu Ching-Tang , Liu Kuan-Yu , Lu Li-Ming , Martin-Cocher Pierre , Meyer-Zhao Zheng , Montaña Alfredo , Moraghan Anthony , Moreno-Nolasco Marcos Emir , Nishioka Hiroaki , Norton Timothy J. , Nystrom George , Ogawa Hideo , Oshiro Peter , Pradel Nicolas , Principe Giacomo , Raffin Philippe , Rodríguez-Montoya Iván , Shaw Paul , Snow William , Sridharan Tirupati Kumara , Srinivasan Ranjani , Wei Ta-Shun , Yu Chen-Yu 
Published: January 2024

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.