Kerr-Newman metric

The Kerr-Newman metric is an exact solution of the Einstein-Maxwell equations of general relativity describing the spacetime geometry around a mass that is both electrically charged and rotating. It is the most general asymptotically flat, stationary solution of those equations, generalizing the uncharged Kerr metric for a rotating black hole by adding the energy of an electromagnetic field. The solution was found by Ezra Newman in 1965, building on Roy Kerr's earlier rotating-black-hole solution. It carries a ring-shaped singularity, and in certain extremal cases has no event horizon at all, exposing a theoretical naked singularity. Because real astrophysical objects do not have perfectly aligned rotation and magnetic axes, and the solution describes no infalling matter, radiation or dark matter, its role is chiefly theoretical rather than a direct model of an observed object.