Kerr-Vaidya black holes

TL;DR

This paper investigates the properties of Kerr-Vaidya black holes, nonstationary extensions of Kerr metrics, analyzing their horizons, energy conditions, and the emergence of firewalls in accreting and evaporating scenarios.

Contribution

It provides a detailed comparison of Kerr-Vaidya metrics with Vaidya solutions, explores horizon locations, and reveals firewall phenomena in dynamic black hole models.

Findings

Apparent horizon in outgoing Kerr-Vaidya matches Kerr black hole.

Ingoing Kerr-Vaidya horizon differs and is numerically located.

Accreting black holes exhibit firewalls with divergent energy densities.

Abstract

Kerr-Vaidya metrics are the simplest nonstationary extensions of the Kerr metric. We explore their properties and compare them with the near-horizon limits of the spherically symmetric self-consistent solutions (the ingoing Vaidya metric with decreasing mass and the outgoing Vaidya metric with increasing mass) for the evaporating and accreting physical black holes. The Newman-Janis transformation relates the corresponding Vaidya and Kerr-Vaidya metrics. For nonzero angular momentum, the energy-momentum tensor violates the null energy condition (NEC). However, we show that its structure differs from the standard form of the NEC-violating tensors. The apparent horizon in the outgoing Kerr-Vaidya metric coincides with that of the Kerr black hole. For the ingoing metric, its location is different. We derive the ordinary differential equation for this surface and locate it numerically. A spherically symmetric accreting black hole leads to a firewall -- a divergent energy density, pressure, and flux as perceived by an infalling observer. We show that this is also true for the outgoing Kerr-Vaidya metric