Tests of General Relativity with the First EHT Sgr A* Images

Horizon scale images of black holes offer the opportunity of testing their metric. We present constraints on potential deviations from the Kerr prediction based on 2017 Event Horizon Telescope (EHT) observations. We calibrate the relationship between the geometrically defined black hole shadow boundary and the observed size of the ring-like images using a large library that includes both Kerr and non-Kerr simulations. We use these bounds to place constraints on metrics that are parametrically different from Kerr as well as on charges of several known spacetime solutions. We compare our results to those from earlier tests of General Relativity in a variety of astrophysical and cosmological settings.