Black-hole hair loss: learning about binary progenitors from ringdown signals

TL;DR

This paper explores how gravitational wave signals from perturbed black holes, specifically the quasi-normal modes, can be used to test general relativity and infer properties of black hole mergers, including progenitor masses.

Contribution

It introduces a practical method to test general relativity using quasi-normal modes and demonstrates how mode amplitudes reveal information about the binary progenitors.

Findings

Relative amplitudes of quasi-normal modes encode progenitor binary masses.

Method can distinguish black hole signals from other sources.

Supports testing of general relativity in strong gravity regimes.

Abstract

Perturbed Kerr black holes emit gravitational radiation, which (for the practical purposes of gravitational-wave astronomy) consists of a superposition of damped sinusoids termed quasi-normal modes. The frequencies and time-constants of the modes depend only on the mass and spin of the black hole - a consequence of the no-hair theorem. It has been proposed that a measurement of two or more quasi-normal modes could be used to confirm that the source is a black hole and to test if general relativity continues to hold in ultra-strong gravitational fields. In this paper we propose a practical approach to testing general relativity with quasi-normal modes. We will also argue that the relative amplitudes of the various quasi-normal modes encode important information about the origin of the perturbation that caused them. This helps in inferring the nature of the perturbation from an observation of the emitted quasi-normal modes. In particular, we will show that the relative amplitudes of the different quasi-normal modes emitted in the process of the merger of a pair of nonspinning black holes can be used to measure the component masses of the progenitor binary.