We consider stationary, axially and equatorially symmetric systems consisting of a central rotating and charged degenerate black hole and surrounding matter. We show that a 2 + Q 2 = M 2 always holds provided that a continuous sequence of spacetimes can be identified, leading from the Kerr–Newman solution in electrovacuum to the solution in question. The quantity a = J/ M is the black hole’s intrinsic angular momentum per unit mass, Q its electric charge and M is the well-known black hole mass parameter introduced by Christodoulou and Ruffini.

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G. Neugebauer

Papers

Stationary axisymmetric electrovacuum fields in general relativity.