Shadows around Sgr A* and M87* as a tool to test gravity theories

Abstract

In the framework of Randall -- Sundrum theory with extra dimension Reissner -- Nordstr\"om black hole solutions with a tidal charge have been found. The shadow around the supermassive black hole in M87 was reconstructed in 2019 based on observations with the Event Horizon Telescope (EHT) in April 2017. In May 2022 the EHT Collaboration presented results of a shadow reconstruction for our Galactic Center. Earlier, for Reissner -- Nordstr\"om metric we derived analytical expressions for shadow size as a function of charge and later generalized these results for a tidal charge case. We discuss opportunities to evaluate parameters of alternative theories of gravity with shadow size estimates done by the EHT Collaboration, in particular, a tidal charge could be estimated from these observations.