Origin of the ring ellipticity in the black hole images of M87 *

Rohan Dahale;Ilje Cho;Kotaro Moriyama;Kaj Wiik;Paul Tiede;Jos?? L. G??mez;Chi-kwan Chan;Roman Gold;Vadim Y. Bernshteyn;Marianna Foschi;Britton Jeter;Hung-Yi Pu;Boris Georgiev;Abhishek V. Joshi;Alejandro Cruz-Osorio;Iniyan Natarajan;Avery E. Broderick;Le??n D. S. Salas;Koushik Chatterjee;Kazunori Akiyama;Ezequiel Albentosa-Ru??z;Antxon Alberdi;Walter Alef;Juan Carlos Algaba;Richard Anantua;Keiichi Asada;Rebecca Azulay;Uwe Bach;Anne-Kathrin Baczko;David Ball;Mislav Balokovi??;Bidisha Bandyopadhyay;John Barrett;Michi Baub??ck;Bradford A. Benson;Dan Bintley;Lindy Blackburn;Raymond Blundell;Katherine L. Bouman;Geoffrey C. Bower;Michael Bremer;Roger Brissenden;Silke Britzen;Dominique Broguiere;Thomas Bronzwaer;Sandra Bustamante;Douglas Ferreira Carlos;John E. Carlstrom;Andrew Chael;Dominic O. Chang;Shami Chatterjee;Ming-Tang Chen;Yongjun Chen;Xiaopeng Cheng;Pierre Christian;Nicholas S. Conroy;John E. Conway;Thomas M. Crawford;Geoffrey B. Crew;Yuzhu Cui;Brandon Curd;Jordy Davelaar;Mariafelicia De Laurentis;Roger Deane;Jessica Dempsey;Gregory Desvignes;Jason Dexter;Vedant Dhruv;Indu K. Dihingia;Sheperd S. Doeleman;Sergio A. Dzib;Ralph P. Eatough;Razieh Emami;Heino Falcke;Joseph Farah;Vincent L. Fish;Edward Fomalont;H. Alyson Ford;Raquel Fraga-Encinas;William T. Freeman;Per Friberg;Christian M. Fromm;Antonio Fuentes;Peter Galison;Charles F. Gammie;Roberto Garc??a;Olivier Gentaz;Gertie Geertsema;Ciriaco Goddi;Arturo I. G??mez-Ruiz;Minfeng Gu;Mark Gurwell;Kazuhiro Hada;Daryl Haggard;Ronald Hesper;Dirk Heumann;Luis C. Ho;Paul Ho;Mareki Honma;Chih-Wei L. Huang;Lei Huang;David H. Hughes;Shiro Ikeda;C. M. Violette Impellizzeri;Makoto Inoue;Sara Issaoun;David J. James;Buell T. Jannuzi;Michael Janssen;Wu Jiang;Alejandra Jim??nez-Rosales;Michael D. Johnson;Svetlana Jorstad;Adam C. Jones;Taehyun Jung;Ramesh Karuppusamy;Tomohisa Kawashima;Garrett K. Keating;Mark Kettenis;Dong-Jin Kim;Jae-Young Kim;Jongsoo Kim;Junhan Kim;Motoki Kino;Jun Yi Koay;Prashant Kocherlakota;Yutaro Kofuji;Patrick M. Koch;Shoko Koyama;Carsten Kramer;Joana A. Kramer;Michael Kramer;Thomas P. Krichbaum;Cheng-Yu Kuo;Noemi La Bella;Sang-Sung Lee;Aviad Levis;Zhiyuan Li;Rocco Lico;Greg Lindahl;Michael Lindqvist;Mikhail Lisakov;Jun Liu;Kuo Liu;Elisabetta Liuzzo;Wen-Ping Lo;Andrei P. Lobanov;Laurent Loinard;Colin J. Lonsdale;Amy E. Lowitz;Ru-Sen Lu;Nicholas R. MacDonald;Jirong Mao;Nicola Marchili;Sera Markoff;Daniel P. Marrone;Alan P. Marscher;Iv??n Mart??-Vidal;Satoki Matsushita;Lynn D. Matthews;Lia Medeiros;Karl M. Menten;Izumi Mizuno;Yosuke Mizuno;Joshua Montgomery;James M. Moran;Monika Moscibrodzka;Wanga Mulaudzi;Cornelia M??ller;Hendrik M??ller;Alejandro Mus;Gibwa Musoke;Ioannis Myserlis;Hiroshi Nagai;Neil M. Nagar;Dhanya G. Nair;Masanori Nakamura;Gopal Narayanan;Antonios Nathanail;Santiago Navarro Fuentes;Joey Neilsen;Chunchong Ni;Michael A. Nowak;Junghwan Oh;Hiroki Okino;H??ctor Ra??l Olivares S??nchez;Tomoaki Oyama;Feryal ??zel;Daniel C. M. Palumbo;Georgios Filippos Paraschos;Jongho Park;Harriet Parsons;Nimesh Patel;Ue-Li Pen;Dominic W. Pesce;Vincent Pi??tu;Aleksandar PopStefanija;Oliver Porth;Ben Prather;Giacomo Principe;Dimitrios Psaltis;Venkatessh Ramakrishnan;Ramprasad Rao;Mark G. Rawlings;Luciano Rezzolla;Angelo Ricarte;Bart Ripperda;Jan R??der;Freek Roelofs;Cristina Romero-Ca??izales;Eduardo Ros;Arash Roshanineshat;Helge Rottmann;Alan L. Roy;Ignacio Ruiz;Chet Ruszczyk;Kazi L. J. Rygl;Salvador S??nchez;David S??nchez-Arg??elles;Miguel S??nchez-Portal;Mahito Sasada;Kaushik Satapathy;Saurabh;Tuomas Savolainen;F. Peter Schloerb;Jonathan Schonfeld;Karl-Friedrich Schuster;Lijing Shao;Zhiqiang Shen;Sasikumar Silpa;Des Small;Bong Won Sohn;Jason SooHoo;Kamal Souccar;Joshua S. Stanway;He Sun;Fumie Tazaki;Alexandra J. Tetarenko;Remo P. J. Tilanus;Michael Titus;Kenji Toma;Pablo Torne;Teresa Toscano;Efthalia Traianou;Tyler Trent;Sascha Trippe;Matthew Turk;Ilse van Bemmel;Huib Jan van Langevelde;Daniel R. van Rossum;Jesse Vos;Jan Wagner;Derek Ward-Thompson;John Wardle;Jasmin E. Washington;Jonathan Weintroub;Robert Wharton;Maciek Wielgus;Gunther Witzel;Michael F. Wondrak;George N. Wong;Qingwen Wu;Nitika Yadlapalli;Paul Yamaguchi;Aristomenis Yfantis;Doosoo Yoon;Andr?? Young;Ziri Younsi;Wei Yu;Feng Yuan;Ye-Fei Yuan;Ai-Ling Zeng;J. Anton Zensus;Shuo Zhang;Guang-Yao Zhao;Shan-Shan Zhao

2025-01-01

---

Abstract

We investigate the origin of the elliptical ring structure observed in the images of the supermassive black hole M87∗, aiming to disentangle contributions from gravitational, astrophysical, and imaging effects. Leveraging the enhanced capabilities of the Event Horizon Telescope (EHT)’s 2018 array, including improved (u, v)-coverage from the Greenland Telescope, we measured the ring’s ellipticity using five independent imaging methods, obtaining a consistent average value of τ = 0.08+−000302 with a position angle of ξ = 50.1−+7662 degrees. To interpret this measurement, we compared it to general relativistic magnetohydrodynamic (GRMHD) simulations spanning a wide range of physical parameters including the thermal or nonthermal electron distribution function, spins, and ion-to-electron temperature ratios in both low- and high-density regions. We find no statistically significant correlation between spin and ellipticity in GRMHD images. Instead, we identify a correlation between ellipticity and the fraction of non-ring emission, particularly in nonthermal models and models with higher jet emission. These results indicate that the ellipticity measured from the M87∗ emission structure is consistent with that expected from simulations of turbulent accretion flows around black holes, where it is dominated by astrophysical effects rather than gravitational ones. Future high-resolution imaging, including space very long baseline interferometry and long-term monitoring, will be essential to isolate gravitational signatures from astrophysical effects.