Nearly extremal apparent horizons in simulations of merging black holes
The spin angular momentum S of an isolated Kerr black hole is bounded by the surface area A of its apparent horizon: 8 pi S A. We show that the overspun surfaces are indeed superextremal: our lower bound on their Booth-Fairhurst extremality exceeds unity. However, we confirm that these superextremal surfaces are always surrounded by marginally outer trapped surfaces (i.e., by apparent horizons) with 8 pi S < A. The extremality lower bound on the enclosing apparent horizon is always less than unity but can exceed the value for an extremal Kerr black hole.
Lovelace, G., M.A. Scheel, R. Owen, et al. 2015. "Nearly extremal apparent horizons in simulations of merging black holes." Classical and Quantum Gravity 32(6): 065007.
Classical and Quantum Gravity
Physics and Astronomy
Numerical relativity, Black hole binaries, Extremality, Apparent horizon