Constraints on a charge in the Reissner-Nordström metric for the black hole at the Galactic Center

Using an algebraic condition of vanishing discriminant for multiple roots of fourth-degree polynomials, we derive an analytical expression of a shadow size as a function of a charge in the Reissner-Nordstr\"om (RN) metric [1,2]. We consider shadows for negative tidal charges and charges correspondin... View More