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Our current understanding of black holes assumes that they are described by the Kerr solution to Einstein’s equations. In April of 2019 the Event Horizon Telescope (EHT) published the first image of a supermassive black hole at the center of the M87 galaxy, resolved to event horizon scales. This image led to a null-hypothesis test of the Kerr metric and to the first constraint on the size of a black-hole shadow, the critical impact parameter between photons that fall into the black hole and those that escape to infinity. I will discuss recent results that used analytic calculations and numerical simulations to place constraints on regular, parametric, non-Kerr metrics. I will show that the shadow-size measurements can be used to place order unity constraints on deviation parameters that can be related to the second Post-Newtonian order and are, therefore, inaccessible to weak-field tests. I will show that spacetimes that deviate from the Kerr metric but satisfy weak-field tests can lead to large deviations in the size of predicted black-hole shadows that are inconsistent with even the current EHT measurements. Furthermore, I will briefly discuss how the same shadow size constraint can be used to constrain known solutions to gravitational theories and how these constraints may be improved with future EHT observations.
Join ZoomGov Meeting: https://bnl.zoomgov.com/j/1605020278?pwd=cHJ1bDRuK1FDNnZLSnpxVkZhcDQ3QT09
Meeting ID: 160 502 0278 Passcode: E=mc2
Host: Hooman Davoudiasl
Contact: elamar@bnl.gov