Monitoring the Morphology of M87* in 2009–2017 with the Event Horizon Telescope
Authors: Wielgus Maciek , Akiyama Kazunori , Blackburn Lindy , Chan Chi-kwan , Dexter Jason , Doeleman Sheperd S. , Fish Vincent L. , Issaoun Sara , Johnson Michael D. , Krichbaum Thomas P. , Lu 路 Ru-Sen 如森 , Pesce Dominic W. , Wong George N. , Bower Geoffrey C. , Broderick Avery E. , Chael Andrew , Chatterjee Koushik , Gammie Charles F. , Georgiev Boris , Hada Kazuhiro , Loinard Laurent , Markoff Sera , Marrone Daniel P. , Plambeck Richard , Weintroub Jonathan , Dexter Matthew , MacMahon David H. E. , Wright Melvyn , Alberdi Antxon , Alef Walter , Asada Keiichi , Azulay Rebecca , Baczko Anne-Kathrin , Ball David , Baloković Mislav , Barausse Enrico , Barrett John , Bintley Dan , Boland Wilfred , Bouman Katherine L. , Bremer Michael , Brinkerink Christiaan D. , Brissenden Roger , Britzen Silke , Broguiere Dominique , Bronzwaer Thomas , Byun Do-Young , Carlstrom John E. , Chatterjee Shami , Chen Ming-Tang , Chen 陈 Yongjun 永军 , Cho Ilje , Christian Pierre , Conway John E. , Cordes James M. , Crew Geoffrey B. , Cui Yuzhu , Davelaar Jordy , Laurentis Mariafelicia De , Deane Roger , Dempsey Jessica , Desvignes Gregory , Dzib Sergio A. , Eatough Ralph P. , Falcke Heino , Fomalont Ed , Fraga-Encinas Raquel , Friberg Per , Fromm Christian M. , Galison Peter , García Roberto , Gentaz Olivier , Goddi Ciriaco , Gold Roman , Gómez José L. , Gómez-Ruiz Arturo I. , Gu 顾 Minfeng 敏峰 , Gurwell Mark , Hecht Michael H. , Hesper Ronald , Ho 何 Luis C. 子山 , Ho Paul , Honma Mareki , Huang Chih-Wei L. , Huang 黄 Lei 磊 , Hughes David H. , Inoue Makoto , James David J. , Jannuzi Buell T. , Janssen Michael , Jeter Britton , Jiang 江 Wu 悟 , Jimenez-Rosales Alejandra , Jorstad Svetlana , Jung Taehyun , Karami Mansour , Karuppusamy Ramesh , Kawashima Tomohisa , Keating Garrett K. , Kettenis Mark , Kim Jae-Young , Kim Junhan , Kim Jongsoo , Kino Motoki , Koay Jun Yi , Koch Patrick M. , Koyama Shoko , Kramer Michael , Kramer Carsten , Kuo Cheng-Yu , Lauer Tod R. , Lee Sang-Sung , Li 李 Yan-Rong 彦荣 , Li 李 Zhiyuan 志远 , Lindqvist Michael , Lico Rocco , Liu Kuo , Liuzzo Elisabetta , Lo Wen-Ping , Lobanov Andrei P. , Lonsdale Colin , MacDonald Nicholas R. , Mao 毛 Jirong 基荣 , Marchili Nicola , Marscher Alan P. , Martí-Vidal Iván , Matsushita Satoki , Matthews Lynn D. , Medeiros Lia , Menten Karl M. , Mizuno Yosuke , Mizuno Izumi , Moran James M. , Moriyama Kotaro , Moscibrodzka Monika , Müller Cornelia , Musoke Gibwa , Nagai Hiroshi , Nagar Neil M. , Nakamura Masanori , Narayan Ramesh , Narayanan Gopal , Natarajan Iniyan , Nathanail Antonios , Neri Roberto , Ni Chunchong , Noutsos Aristeidis , Okino Hiroki , Olivares Héctor , Ortiz-León Gisela N. , Oyama Tomoaki , Özel Feryal , Palumbo Daniel C. M. , Park Jongho , Patel Nimesh , Pen Ue-Li , Piétu Vincent , PopStefanija Aleksandar , Porth Oliver , Prather Ben , Preciado-López Jorge A. , Psaltis Dimitrios , Pu Hung-Yi , Ramakrishnan Venkatessh , Rao Ramprasad , Rawlings Mark G. , Raymond Alexander W. , Rezzolla Luciano , Ripperda Bart , Roelofs Freek , Rogers Alan , Ros Eduardo , Rose Mel , Roshanineshat Arash , Rottmann Helge , Roy Alan L. , Ruszczyk Chet , Ryan Benjamin R. , Rygl Kazi L. J. , Sánchez Salvador , Sánchez-Arguelles David , Sasada Mahito , Savolainen Tuomas , Schloerb F. Peter , Schuster Karl-Friedrich , Shao Lijing , Shen 沈 Zhiqiang 志强 , Small Des , Sohn Bong Won , SooHoo Jason , Tazaki Fumie , Tiede Paul , Tilanus Remo P. J. , Titus Michael , Toma Kenji , Torne Pablo , Trent Tyler , Traianou Efthalia , Trippe Sascha , Tsuda Shuichiro , Bemmel Ilse van , van Langevelde Huib Jan , van Rossum Daniel R. , Wagner Jan , Wardle John , Ward-Thompson Derek , Wex Norbert , Wharton Robert , Wu 吴 Qingwen 庆文 , Yoon Doosoo , Young André , Young Ken , Younsi Ziri , Yuan 袁 Feng 峰 , Yuan 袁 Ye-Fei 业飞 , Zensus J. Anton , Zhao Guangyao , Zhao Shan-Shan , Zhu Ziyan 
Published: September 2020

Abstract
The Event Horizon Telescope (EHT) has recently delivered the first resolved images of M87*, the supermassive black hole in the center of the M87 galaxy. These images were produced using 230 GHz observations performed in 2017 April. Additional observations are required to investigate the persistence of the primary image feature—a ring with azimuthal brightness asymmetry—and to quantify the image variability on event horizon scales. To address this need, we analyze M87* data collected with prototype EHT arrays in 2009, 2011, 2012, and 2013. While these observations do not contain enough information to produce images, they are sufficient to constrain simple geometric models. We develop a modeling approach based on the framework utilized for the 2017 EHT data analysis and validate our procedures using synthetic data. Applying the same approach to the observational data sets, we find the M87* morphology in 2009–2017 to be consistent with a persistent asymmetric ring of ∼40 μas diameter. The position angle of the peak intensity varies in time. In particular, we find a significant difference between the position angle measured in 2013 and 2017. These variations are in broad agreement with predictions of a subset of general relativistic magnetohydrodynamic simulations. We show that quantifying the variability across multiple observational epochs has the potential to constrain the physical properties of the source, such as the accretion state or the black hole spin.