Black Hole Ringing, Quasinormal Modes, and Light Rings

TL;DR

This paper critically examines the connection between black hole light rings and gravitational wave quasinormal modes, highlighting that their relationship is model-dependent and exploring implications for rotating black holes.

Contribution

It challenges the assumed direct link between light rings and quasinormal modes, emphasizing the need for refined models especially for Kerr black holes.

Findings

The light ring does not uniquely determine quasinormal modes.

Model history influences the perceived connection between light rings and spacetime ringing.

Understanding dissociation is crucial for rotating black hole astrophysics.

Abstract

Modelling of gravitational waves from binary black hole inspiral has played an important role in the recent observations of such signals. The late-stage ringdown phase of the gravitational waveform is often associated with the null particle orbit ("light ring") of the black hole spacetime. With simple models we show that this link between the light ring and spacetime ringing is based more on the history of specific models than on an actual constraining relationship. We also show, in particular, that a better understanding of the dissociation of the two may be relevant to the astrophysically interesting case of rotating (Kerr) black holes.