Superradiance in deformed Kerr black holes

TL;DR

This paper investigates superradiance phenomena in deformed Kerr black holes, showing how small deviations from Kerr can enhance superradiance and affect instability timescales, with implications for testing general relativity.

Contribution

It provides the first analysis of superradiance and instability timescales in Kerr-like spacetimes with deformation parameters, extending understanding beyond classical Kerr black holes.

Findings

Superradiance is suppressed for large deformations.

Small deformations can enhance superradiance.

Deformation affects the instability timescale.

Abstract

Ongoing observations in the strong-field regime are in optimal agreement with general relativity, although current errors still leave room for small deviations from Einstein's theory. Here we summarise our recent results on superradiance of scalar and electromagnetic test fields in Kerr-like spacetimes, focusing mainly on the Konoplya--Zhidenko metric. We observe that, while for large deformations with respect to the Kerr case superradiance is suppressed, it can be nonetheless enhanced for small deformations. We also study the superradiant instability caused by massive scalar fields, and we provide a first estimate of the effect of the deformation on the instability timescale.