Superradiance Instabilities of Charged Black Holes in Einstein-Maxwell-scalar Theory

TL;DR

This paper investigates superradiant instabilities of charged black holes in Einstein-Maxwell-scalar theory by analyzing scalar perturbations, revealing that certain modes are amplified and cause instability due to potential well trapping.

Contribution

It introduces the study of superradiant instabilities in charged hairy black holes with double-peak potentials, highlighting the mechanism of mode amplification and instability.

Findings

Superradiant modes are trapped and amplified in a double-peak potential.

Charged hairy black holes become unstable due to superradiant amplification.

The instability results from competition between tunneling and leakage of modes.

Abstract

We study time evolutions of charged scalar perturbations on the background of a charged hairy black hole, in which the perturbations can be governed by a double-peak effective potential. By extracting quasinormal modes from the waveform of scalar perturbations, we discover that some quasinormal modes, which are trapped in a potential well between two potential peaks, can be superradiantly amplified. These superradiant modes make the hairy black hole unstable against charged scalar perturbations. Moreover, it is found that the superradiant modes arise from the competition between the superradiant amplification caused by tunneling through the outer potential barrier and the leakage of modes through the inner potential barrier into the black hole.