Ringdown signatures in the Ernst-Wild geometry: modeling Kerr black holes immersed in a magnetic field

TL;DR

This paper investigates how a magnetic field surrounding Kerr black holes affects their quasinormal modes and ringdown signals, providing a new template to interpret gravitational wave data in magnetized environments.

Contribution

It introduces a perturbative approach to model Kerr black holes in magnetic fields and constructs a ringdown template accounting for magnetosphere effects.

Findings

Magnetic fields alter the quasinormal mode spectrum of Kerr black holes.

The developed template improves the interpretation of ringdown signals in magnetized environments.

Magnetosphere effects can influence gravitational wave data analysis.

Abstract

We analyze the quasinormal mode spectrum for Kerr black holes surrounded by an asymptotically uniform magnetic field, modeled with the Ernst-Wild geometry. A perturbative expansion in both the rotation parameter $a$ and the magnetic field $B$ allows the analysis of perturbations with Kerr-like asymptotics well inside the Melvin radius, and we obtain the spectrum for a variety of scalar quasinormal modes over a range of parameters using the continued fraction method. We then interpolate the low-lying mode spectrum to construct an Ernst-Wild template for the ringdown, and use the LIGO-Virgo-KAGRA analysis tool pyRing to assess the impact of the magnetosphere on the extraction of ringdown signatures from several observed binary black hole mergers.