Extremality conditions for isolated and dynamical horizons
A maximally rotating Kerr black hole is said to be extremal. In this paper we introduce the corresponding restrictions for isolated and dynamical horizons. These reduce to the standard notions for Kerr but in general do not require the horizon to be either stationary or rotationally symmetric. We consider physical implications and applications of these results. In particular we introduce a parameter e which characterizes how close a horizon is to extremality and should be calculable in numerical simulations.
©2008 The American Physical Society. (Received 14 September 2007; published 7 April 2008) We would like to thank Peter Booth, Patrick Brady, Jolien Creighton, Herb Gaskill and Badri Krishnan for helpful discussions. Ivan Booth was supported by the Natural Sciences and Engineering Research Council of Canada. Stephen Fairhurst was supported by NSF Grant No. PHY-0200852 and the Royal Society.