General Relativity/Reissner-Nordström black hole
It is described by the electric field of a point-like charged particle, and especially by the Reissner-Nordström metric that generalizes the Schwarzschild metric of an electrically neutral black hole:
The electromagnetic potential is
While the charged black holes with (especially with ) are similar to the Schwarzschild black hole, they have two horizons: the event horizon and an internal Cauchy horizon. The horizons are located at . These horizons merge for which is the case of an extremal black hole.