Superradiance and instabilities in black holes surrounded by anisotropic fluids

TL;DR

This paper investigates superradiance and instabilities of charged scalar fields around Reissner-Nordström black holes with anisotropic fluids, revealing conditions for superradiant scattering and unstable modes through analytical and numerical analysis.

Contribution

It introduces the study of superradiance and instabilities in black holes surrounded by anisotropic fluids, extending previous work to new astrophysical scenarios.

Findings

Superradiant scattering condition matches the de Sitter case.

Analytical solutions for quasinormal frequencies are identified.

Unstable modes are confirmed through numerical analysis.

Abstract

In this paper we analyze the propagation of a charged scalar field in a Reissner-Nordstr\"om black hole endowed with one anisotropic fluid that can play the role of a cosmological term for certain set of parameters. The evolution of a scalar wave scattering is examined giving rise to the same superradiant scattering condition as in the de Sitter case. In addition, an analysis of the modes coming from the application of quasinormal boundary conditions is presented. Some special cases displaying analytical solutions for the quasinormal frequencies are discussed. Moreover, the superradiant condition is adapted to the quasinormal problem triggering unstable modes, what is confirmed by our numerical analysis.