Superradiance in Kerr-like black holes

TL;DR

This paper investigates superradiance phenomena around Kerr-like black holes, revealing how deviations from Kerr spacetime affect superradiant amplification and stability, with implications for testing gravity theories.

Contribution

It introduces the study of superradiance in Kerr-like black holes and analyzes how deformation parameters influence superradiant amplification and instability.

Findings

Superradiance is suppressed for large deformation parameters.

Certain small deformations lead to higher amplification than Kerr.

First analysis of superradiant instability in non-Kerr spacetimes.

Abstract

Recent strong-field regime tests of gravity are so far in agreement with general relativity. In particular, astrophysical black holes appear all to be consistent with the Kerr spacetime, but the statistical error on current observations allows for small yet detectable deviations from this description. Here we study superradiance of scalar and electromagnetic test fields around the Kerr-like Konoplya--Zhidenko black hole and we observe that for large values of the deformation parameter superradiance is highly suppressed with respect to the Kerr case. Surprisingly, there exists a range of small values of the deformation parameter for which the maximum amplification factor is larger than the Kerr one. We also provide a first result about the superradiant instability of these non-Kerr spacetimes against massive scalar fields.