Horizon dynamics of distorted rotating black holes

TL;DR

This paper uses numerical simulations to study the complex horizon dynamics of a perturbed rotating black hole, revealing multiple trapped surfaces and analyzing their properties within the dynamical horizon framework.

Contribution

It provides new insights into the behavior of marginally outer trapped surfaces and horizon flux laws during strong perturbations of Kerr black holes.

Findings

Up to five concentric marginally outer trapped surfaces observed.

Trapped surfaces appear and disappear in pairs, with an odd total number at any time.

Event horizon remains well-behaved, approaching the apparent horizon before and after dynamical phases.

Abstract

We present numerical simulations of a Kerr black hole perturbed by a pulse of ingoing gravitational radiation. For strong perturbations we find up to five concentric marginally outer trapped surfaces. These trapped surfaces appear and disappear in pairs, so that the total number of such surfaces at any given time is odd. The world tubes traced out by the marginally outer trapped surfaces are found to be spacelike during the highly dynamical regime, approaching a null hypersurface at early and late times. We analyze the structure of these marginally trapped tubes in the context of the dynamical horizon formalism, computing the expansion of outgoing and incoming null geodesics, as well as evaluating the dynamical horizon flux law and the angular momentum flux law. Finally, we compute the event horizon. The event horizon is well-behaved and approaches the apparent horizon before and after the highly dynamical regime. No new generators enter the event horizon during the simulation.