Psaltis, DimitriosMedeiros, LiaChristian, PierreOzel, FeryalAkiyama, KazunoriAlberdi, AntxonAlef, WalterAsada, KeiichiAzulay, RebeccaBall, DavidBalokovic, MislavBarrett, JohnBintley, DanBlackburn, LindyBoland, WilfredBower, Geoffrey C.Bremer, MichaelBrinkerink, Christiaan D.Brissenden, RogerBritzen, SilkeBroguiere, DominiqueBronzwaer, ThomasByun, Do-YoungCarlstrom, John E.Chael, AndrewChan, Chi-kwanChatterjee, ShamiChatterjee, KoushikChen, Ming-TangChen, YongjunCho, IljeConway, John E.Cordes, James M.Crew, Geoffrey B.Cui, YuzhuDavelaar, JordyDe Laurentis, MariafeliciaDeane, RogerDempsey, JessicaDesvignes, GregoryDexter, JasonEatough, Ralph P.Falcke, HeinoFish, Vincent L.Fomalont, EdFraga-Encinas, RaquelFriberg, PerFromm, Christian M.Gammie, Charles F.García, RobertoGentaz, OlivierGoddi, CiriacoGomez, Jose L.Gu, MinfengGurwell, MarkHada, KazuhiroHesper, RonaldHo, Luis C.Ho, PaulHonma, MarekiHuang, Chih-Wei L.Huang, LeiHughes, David H.Inoue, MakotoIssaoun, SaraJames, David J.Jannuzi, Buell T.Janssen, MichaelJiang, WuJimenez-Rosales, AlejandraJohnson, Michael D.Jorstad, SvetlanaJung, TaehyunKarami, MansourKaruppusamy, RameshKawashima, TomohisaKeating, Garrett K.Kettenis, MarkKim, Jae-YoungKim, JunhanKim, JongsooKino, MotokiKoay, Jun YiKoch, Patrick M.Koyama, ShokoKramer, MichaelKramer, CarstenKrichbaum, Thomas P.Kuo, Cheng-YuLauer, Tod R.Lee, Sang-SungLi, Yan-RongLi, ZhiyuanLindqvist, MichaelLico, RoccoLiu, JunLiu, KuoLiuzzo, ElisabettaLo, Wen-PingLobanov, Andrei P.Lonsdale, ColinLu, Ru-SenMao, JirongMarkoff, SeraMarrone, Daniel P.Marscher, Alan P.Marti-Vidal, IvanMatsushita, SatokiMizuno, YosukeMizuno, IzumiMoran, James M.Moriyama, KotaroMoscibrodzka, MonikaMuller, CorneliaMusoke, GibwaMus Mejias, AlejandroNagai, HiroshiNagar, Neil M.Narayan, RameshNarayanan, GopalNatarajan, IniyanNeri, RobertoNoutsos, AristeidisOkino, HirokiOlivares, HectorOyama, TomoakiPalumbo, Daniel C.M.Park, JonghoPatel, NimeshPen, Ue-LiPietu, VincentPlambeck, RichardPopStefanija, AleksandarPrather, BenPreciado-Lopez, Jorge A.Ramakrishnan, VenkatesshRao, RamprasadRawlings, Mark G.Raymond, Alexander W.Ripperda, BartRoelofs, FreekRogers, AlanRos, EduardoRose, MelRoshanineshat, ArashRottmann, HelgeRoy, Alan L.Ruszczyk, ChetRyan, Benjamin R.Rygl, Kazi L.J.Sanchez, SalvadorSanchez-Arguelles, DavidSasada, MahitoSavolainen, TuomasSchloerb, F. PeterSchuster, Karl-FriedrichShao, LijingShen, ZhiqiangSmall, DesSohn, Bong WonSooHoo, JasonTazaki, FumieTilanus, Remo P.J.Titus, MichaelTorne, PabloTrent, TylerTraianou, EfthaliaTrippe, SaschaVan Bemmel, IlseVan Langevelde, Huib JanVan Rossum, Daniel R.Wagner, JanWardle, JohnWard-Thompson, DerekWeintroub, JonathanWex, NorbertWharton, RobertWielgus, MaciekWong, George N.Wu, QingwenYoon, DoosooYoung, AndreYounsi, ZiriYuan, FengYuan, Ye-FeiZhao, Shan-Shan2021-12-092021-12-092020-10-01Psaltis, D, Medeiros, L & Christian, P 2020, 'Gravitational test beyond the first post-newtonian order with the shadow of the M87 black hole', Physical Review Letters, vol. 125, art. 141104, pp. 1-9.0031-9007 (print)1079-7114 (online)10.1103/PhysRevLett.125.141104http://hdl.handle.net/2263/83007The 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.en© 2020 American Physical SocietyEvent Horizon Telescope (EHT)M87Gravitational wavesStellar-mass sourcesArticle