Kerr–Newman metric
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The Kerr–Newman metric describes the spacetime geometry around a mass that is electrically charged and rotating. It is a vacuum solution that generalizes the Kerr metric (which describes an uncharged, rotating mass) by additionally taking into account the energy of an electromagnetic field, making it the most general asymptotically flat and stationary solution of the Einstein–Maxwell equations in general relativity. As an electrovacuum solution, it only includes those charges associated with the magnetic field; it does not include any free electric charges.
The Kerr–Newman metric is primarily of theoretical interest. Astronomical objects have axes for rotation and for magnetic fields, but the metric is only valid for co-aligned axes. The model lacks description of infalling baryonic matter, light (null dusts) or dark matter, and thus provides an incomplete description of stellar mass black holes and active galactic nuclei. The solution however is of mathematical interest and provides a fairly simple cornerstone for further exploration.