Measuring the Ellipticity of M87* Images

Abstract The Event Horizon Telescope (EHT) images of the supermassive black hole at center galaxy M87 provided first image accretion environment on horizon scales. General relativity (GR) predicts that shadow should be nearly circular given inclination angle M87*. A robust detection ellipticity in reconstructions M87* could signal new gravitational physics Here we analyze whether imaging parameters used EHT analyses are sensitive to ring ellipticity, and measure constraints We find top set is unable recover ellipticity. Even for simple geometric models, true biased low, preferring rings. Therefore, place a constraint M87*, 550 synthetic data sets produced from GRMHD simulations. with intrinsic axis ratios 2:1 consistent seen reconstructions.