Scalar perturbations around rotating regular black holes and wormholes: quasi-normal modes, ergoregion instability and superradiance

TL;DR

This paper investigates scalar perturbations around rotating regular black holes and wormholes, analyzing their stability, superradiance effects, and quasi-normal modes to understand their physical properties and differences from Kerr black holes.

Contribution

It provides the first detailed analysis of scalar perturbations on rotating regular black holes and wormholes, including stability and superradiance characteristics.

Findings

Regular black holes are stable under scalar perturbations.

Wormholes exhibit unstable modes, indicating potential instability.

Superradiance occurs but is weaker than in Kerr black holes.

Abstract

We study scalar test-field perturbations on top of a Kerr--black-bounce background, i.e. a family of rotating regular black holes and/or rotating traversable wormholes that can mimic Kerr black holes. We compute the quasi-normal modes for a massless field in both the regular black holes and wormhole branches, confirming the stability of the former and identifying a set of growing modes that renders the latter unstable. We further compute the superradiance amplification factors, for massless and massive fields, in the regular black hole branch, confirming that these objects superradiate, though to a lesser degree than the corresponding Kerr black holes.