First M87 Event Horizon Telescope Results. VIII. Magnetic Field Structure near The Event Horizon
Kazunori Akiyama, Juan Carlos Algaba, A. Alberdi, W. Alef, Richard Anantua, Keiichi Asada, Rebecca Azulay, Anne-Kathrin Baczko, David Ball, Mislav Baloković, John Barrett, B. A. Benson, Dan Bintley, Lindy Blackburn, R. Blundell, W. Boland, Katherine L. Bouman, Geoffrey C. Bower, Hope Boyce, Michael Bremer, Christiaan D. Brinkerink, Roger Brissenden, S. Britzen, Avery E. Broderick, Dominique Broguière, Thomas Bronzwaer, Do‐Young Byun, J. E. Carlstrom, Andrew Chael, Chi‐kwan Chan, Shami Chatterjee, Koushik Chatterjee, Ming‐Tang Chen, Xiaopeng Cheng, Paul M. Chesler, Ilje Cho, Pierre Christian, J. E. Conway, J. M. Cordes, T. M. Crawford, G. Crew, Alejandro Cruz-Osorio, Yuzhu Cui, Jordy Davelaar, Mariafelicia De Laurentis, Roger Deane, Jessica Dempsey, G. Desvignes, Jason Dexter, Sheperd S. Doeleman, Ralph P. Eatough, H. Falcke, Joseph Farah, Vincent L. Fish, E. B. Fomalont, H. Alyson Ford, Raquel Fraga-Encinas, Per Friberg, Christian M. Fromm, Antonio Fuentes, Peter Galison, Charles F. Gammie, Roberto García, Zachary Gelles, Olivier Gentaz, Boris Georgiev, C. Goddi, Roman Gold, José L. Gómez, Arturo I. Gómez-Ruiz, Minfeng Gu, Mark Gurwell, Kazuhiro Hada, Daryl Haggard, M. H. Hecht, Ronald Hesper, Elizabeth Himwich, Luis C. Ho, Paul T. P. Ho, Mareki Honma, Chih-Wei L. Huang, Lei Huang, D. H. Hughes, Shiro Ikeda, Makoto Inoue, Sara Issaoun, D. J. James, Buell T. Jannuzi, Michaël Janssen, Britton Jeter, Wu Jiang, Alejandra Jiménez-Rosales, Michael D. Johnson, Svetlana G. Jorstad, Taehyun Jung, Mansour Karami, R. Karuppusamy, Tomohisa Kawashima, Garrett K. Keating, Mark Kettenis
Abstract
Abstract Event Horizon Telescope (EHT) observations at 230 GHz have now imaged polarized emission around the supermassive black hole in M87 on event-horizon scales. This polarized synchrotron radiation probes the structure of magnetic fields and the plasma properties near the black hole. Here we compare the resolved polarization structure observed by the EHT, along with simultaneous unresolved observations with the Atacama Large Millimeter/submillimeter Array, to expectations from theoretical models. The low fractional linear polarization in the resolved image suggests that the polarization is scrambled on scales smaller than the EHT beam, which we attribute to Faraday rotation internal to the emission region. We estimate the average density n e ∼ 10 4–7 cm −3 , magnetic field strength B ∼ 1–30 G, and electron temperature T e ∼ (1–12) × 10 10 K of the radiating plasma in a simple one-zone emission model. We show that the net azimuthal linear polarization pattern may result from organized, poloidal magnetic fields in the emission region. In a quantitative comparison with a large library of simulated polarimetric images from general relativistic magnetohydrodynamic (GRMHD) simulations, we identify a subset of physical models that can explain critical features of the polarimetric EHT observations while producing a relativistic jet of sufficient power. The consistent GRMHD models are all of magnetically arrested accretion disks, where near-horizon magnetic fields are dynamically important. We use the models to infer a mass accretion rate onto the black hole in M87 of (3–20) × 10 −4 M ⊙ yr −1 .