Gravitational Test beyond the First Post-Newtonian Order with the Shadow of the M87 Black Hole

Psaltis D.;Medeiros L.;Christian P.;Ozel F.;Akiyama K.;Alberdi A.;Alef W.;Asada K.;Azulay R.;Ball D.;Balokovic M.;Barrett J.;Bintley D.;Blackburn L.;Boland W.;Bower G. C.;Bremer M.;Brinkerink C. D.;Brissenden R.;Britzen S.;Broguiere D.;Bronzwaer T.;Byun D. -Y.;Carlstrom J. E.;Chael A.;Chan C. -K.;Chatterjee S.;Chatterjee K.;Chen M. -T.;Chen Y.;Cho I.;Conway J. E.;Cordes J. M.;Crew G. B.;Cui Y.;Davelaar J.;De Laurentis M.;Deane R.;Dempsey J.;Desvignes G.;Dexter J.;Eatough R. P.;Falcke H.;Fish V. L.;Fomalont E.;Fraga-Encinas R.;Friberg P.;Fromm C. M.;Gammie C. F.;Garcia R.;Gentaz O.;Goddi C.;Gomez J. L.;Gu M.;Gurwell M.;Hada K.;Hesper R.;Ho L. C.;Ho P.;Honma M.;Huang C. -W. L.;Huang L.;Hughes D. H.;Inoue M.;Issaoun S.;James D. J.;Jannuzi B. T.;Janssen M.;Jiang W.;Jimenez-Rosales A.;Johnson M. D.;Jorstad S.;Jung T.;Karami M.;Karuppusamy R.;Kawashima T.;Keating G. K.;Kettenis M.;Kim J. -Y.;Kim J.;Kim J.;Kino M.;Koay J. Y.;Koch P. M.;Koyama S.;Kramer M.;Kramer C.;Krichbaum T. P.;Kuo C. -Y.;Lauer T. R.;Lee S. -S.;Li Y. -R.;Li Z.;Lindqvist M.;Lico R.;Liu J.;Liu K.;Liuzzo E.;Lo W. -P.;Lobanov A. P.;Lonsdale C.;Lu R. -S.;Mao J.;Markoff S.;Marrone D. P.;Marscher A. P.;Marti-Vidal I.;Matsushita S.;Mizuno Y.;Mizuno I.;Moran J. M.;Moriyama K.;Moscibrodzka M.;Muller C.;Musoke G.;Mus Mejias A.;Nagai H.;Nagar N. M.;Narayan R.;Narayanan G.;Natarajan I.;Neri R.;Noutsos A.;Okino H.;Olivares H.;Oyama T.;Palumbo D. C. M.;Park J.;Patel N.;Pen U. -L.;Pietu V.;Plambeck R.;Popstefanija A.;Prather B.;Preciado-Lopez J. A.;Ramakrishnan V.;Rao R.;Rawlings M. G.;Raymond A. W.;Ripperda B.;Roelofs F.;Rogers A.;Ros E.;Rose M.;Roshanineshat A.;Rottmann H.;Roy A. L.;Ruszczyk C.;Ryan B. R.;Rygl K. L. J.;Sanchez S.;Sanchez-Arguelles D.;Sasada M.;Savolainen T.;Schloerb F. P.;Schuster K. -F.;Shao L.;Shen Z.;Small D.;Sohn B. W.;Soohoo J.;Tazaki F.;Tilanus R. P. J.;Titus M.;Torne P.;Trent T.;Traianou E.;Trippe S.;Van Bemmel I.;Van Langevelde H. J.;Van Rossum D. R.;Wagner J.;Wardle J.;Ward-Thompson D.;Weintroub J.;Wex N.;Wharton R.;Wielgus M.;Wong G. N.;Wu Q.;Yoon D.;Young A.;Young K.;Younsi Z.;Yuan F.;Yuan Y. -F.;Zhao S. -S.

2020-01-01

---

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.