Escape probability of a photon emitted near the black hole horizon

TL;DR

This paper analyzes the probability of photons escaping from near the horizon of Kerr-Newman black holes, revealing that for extremal black holes with high spin, the escape probability remains significant, reaching up to approximately 29.1%.

Contribution

It provides a detailed calculation of photon escape probabilities near black hole horizons, highlighting the dependence on black hole spin and extremality, which was not previously quantified.

Findings

Escape probability is nonzero near extremal black holes with high spin.

Maximum escape probability (~29.1%) occurs at extremal Kerr black holes.

Escape probability is zero near the horizon for lower spin or subextremal black holes.

Abstract

We investigate the escape of photons from the vicinity of the horizon to infinity in the Kerr-Newmann black hole spacetime. We assume that a light source is at rest in a locally nonrotating frame and photons are emitted isotropically. Then, we evaluate the escape probability of the emitted photons. The main result of this paper is the following. If the black hole is extremal with the nondimensional spin parameter $a_*> 1/2$, however close to the horizon the light source would be, the escape probability remains nonzero. The near-horizon limit value of the escape probability is a monotonically increasing function of $a_*$ and takes a maximum $\sim$29.1\% at $a_*=1$, i.e., for the extremal Kerr case. On the other hand, if the black hole is extremal with $0\leq a_*\leq 1/2$ or if the black hole is subextremal, the near-horizon limit value is zero.