Scalar, Electromagnetic and Gravitational Perturbations of Kerr-Newman Black Holes in the Slow-Rotation Limit

TL;DR

This paper analyzes scalar, electromagnetic, and gravitational perturbations of Kerr-Newman black holes in the slow-rotation limit, deriving perturbation equations and computing quasinormal modes to study stability.

Contribution

It provides the first detailed derivation of perturbation equations and quasinormal modes for Kerr-Newman black holes in the slow-rotation approximation, extending previous analyses.

Findings

Axial and polar sectors are isospectral at first order in spin

First self-consistent stability analysis of Kerr-Newman metric

Derived perturbation equations for gravito-electromagnetic case

Abstract

In Einstein-Maxwell theory, according to classic uniqueness theorems, the most general stationary black-hole solution is the axisymmetric Kerr-Newman metric, which is defined by three parameters: mass, spin and electric charge. The radial and angular dependence of gravitational and electromagnetic perturbations in the Kerr-Newman geometry do not seem to be separable. In this paper we circumvent this problem by studying scalar, electromagnetic and gravitational perturbations of Kerr-Newman black holes in the slow-rotation limit. We extend (and provide details of) the analysis presented in a recent Letter [arXiv:1304.1160]. Working at linear order in the spin, we present the first detailed derivation of the axial and polar perturbation equations in the gravito-electromagnetic case, and we compute the corresponding quasinormal modes for any value of the electric charge. Our study is the first self-consistent stability analysis of the Kerr-Newman metric, and in principle it can be extended to any order in the small rotation parameter. We find numerical evidence that the axial and polar sectors are isospectral at first order in the spin, and speculate on the possible implications of this result.