http://arxiv.org/abs/1505.04189
Kerr black holes have their angular momentum, $J$, bounded by their mass, $M$: $Jc\leqslant GM^2$. There are, however, known black hole solutions violating this Kerr bound. We propose a very simple universal bound on the rotation, rather than on the angular momentum, of four-dimensional, stationary and axisymmetric, asymptotically flat black holes, given in terms of an appropriately defined horizon linear velocity, $v_H$. The $v_H$ bound is simply that $v_H$ cannot exceed the velocity of light. We verify the $v_H$ bound for known black hole solutions, including some that violate the Kerr bound, and conjecture that only extremal Kerr black holes saturate the $v_H$ bound.
C. Herdeiro and E. Radu
Tue, 19 May 15
77/78
Comments: 10 pages, 2 figures, Essay written for the Gravity Research Foundation 2015 Awards for Essays on Gravitation and selected for Honorable Mention
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