Quasinormal modes of Kerr-Newman black holes: coupling of electromagnetic and gravitational perturbations

TL;DR

This paper numerically computes quasinormal modes of Kerr-Newman black holes, compares different approximation methods for electromagnetic and gravitational perturbations, and evaluates the accuracy of the Dudley-Finley equation for astrophysical scenarios.

Contribution

It provides the first numerical computation of Kerr-Newman quasinormal modes in the scalar case and assesses the validity of approximation methods for perturbations.

Findings

Dudley-Finley equation approximates Kerr-Newman dynamics well for Q<M/2

Separable scalar perturbation equations are used for numerical computation

Dudley-Finley equation is suitable for astrophysical applications but not for elementary particle models.

Abstract

We compute numerically the quasinormal modes of Kerr-Newman black holes in the scalar case, for which the perturbation equations are separable. Then we study different approximations to decouple electromagnetic and gravitational perturbations of the Kerr-Newman metric, computing the corresponding quasinormal modes. Our results suggest that the Teukolsky-like equation derived by Dudley and Finley gives a good approximation to the dynamics of a rotating charged black hole for Q<M/2. Though insufficient to deal with Kerr-Newman based models of elementary particles, the Dudley-Finley equation should be adequate for astrophysical applications.