Superradiance instabilities of charged black holes in Einstein-Maxwell-scalar theory

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.

Scalarized Kerr-Newman black holes

“…Furthermore, the presence of multiple photon spheres in a spacetime also suggests the existence of long-lived modes that may render the spacetime unstable [72][73][74][75][76]. Specifically, it has been shown that the existence of multiple photon spheres outside the event horizon can induce superradiance instabilities for charged scalar perturbations [77]. For a more detailed analysis of black holes with multiple photon spheres, we refer readers to the work [78].…”