The Reissner-Nordström metric is the spherically symmetric metric tensor on a Lorentzian manifold for an
electrovacuum with mass and total charge
. Its static line element is
where .
For electric and magnetic charges,
. When
, the two horizon radii are
The exterior has , and
gives the Schwarzschild
metric. The charged Penrose inequality
compares enclosing area with the outer radius in this model.