@article{545a0235c955459590eeba19a432d26c,
title = "Gravitational Test beyond the First Post-Newtonian Order with the Shadow of the M87 Black Hole",
abstract = "The 2017 Event Horizon Telescope (EHT) observations of the central source in M87 have led to the first measurement of the size of a black-hole shadow. This observation offers a new and clean gravitational test of the black-hole metric in the strong-field regime. We show analytically that spacetimes that deviate from the Kerr metric but satisfy weak-field tests can lead to large deviations in the predicted black-hole shadows that are inconsistent with even the current EHT measurements. We use numerical calculations of regular, parametric, non-Kerr metrics to identify the common characteristic among these different parametrizations that control the predicted shadow size. We show that the shadow-size measurements place significant constraints on deviation parameters that control the second post-Newtonian and higher orders of each metric and are, therefore, inaccessible to weak-field tests. The new constraints are complementary to those imposed by observations of gravitational waves from stellar-mass sources.",
author = "{(EHT Collaboration)} and Dimitrios Psaltis and Lia Medeiros and Pierre Christian and Feryal {\"O}zel and Kazunori Akiyama and Antxon Alberdi and Walter Alef and Keiichi Asada and Rebecca Azulay and David Ball and Mislav Balokovi{\'c} and John Barrett and Dan Bintley and Lindy Blackburn and Wilfred Boland and Bower, {Geoffrey C.} and Michael Bremer and Brinkerink, {Christiaan D.} and Roger Brissenden and Silke Britzen and Dominique Broguiere and Thomas Bronzwaer and Byun, {Do Young} and Carlstrom, {John E.} and Andrew Chael and Chan, {Chi Kwan} and Shami Chatterjee and Koushik Chatterjee and Chen, {Ming Tang} and Yongjun Chen and Ilje Cho and Conway, {John E.} and Cordes, {James M.} and Crew, {Geoffrey B.} and Yuzhu Cui and Jordy Davelaar and {De Laurentis}, Mariafelicia and Roger Deane and Jessica Dempsey and Gregory Desvignes and Jason Dexter and Eatough, {Ralph P.} and Heino Falcke and Fish, {Vincent L.} and Ed Fomalont and Raquel Fraga-Encinas and Per Friberg and Jannuzi, {Buell T.} and Marrone, {Daniel P.} and Tilanus, {Remo P.J.}",
note = "Publisher Copyright: {\textcopyright} 2020 American Physical Society.",
year = "2020",
month = oct,
doi = "10.1103/PhysRevLett.125.141104",
language = "English (US)",
volume = "125",
journal = "Physical review letters",
issn = "0031-9007",
publisher = "American Physical Society",
number = "14",
}