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Reissner-NordstrÝm black hole
In physics and astronomy, a Reissner-NordstrÝm black hole is a black hole that carries electric charge Q, no angular momentum, and mass M. General properties of such a black hole are described in the article charged black hole.
It is described by the electric field of a point-like charged particle, and especially by the Reissner-NordstrÝm metric that generalizes the Schwarzschild metric of an electrically neutral black hole:
The electromagnetic potential is
While the charged black holes with | Q | < M (especially with | Q | < < M) 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 | Q | = M which is the case of an extremal black hole.
The black holes with | Q | > M are believed not to exist in Nature because they would contain a naked singularity; their appearance would contradict Roger Penrose's cosmic censorship hypothesis which is generally believed to be true. Theories with supersymmetry usually guarantee that such "superextremal" black holes can't exist.
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