All you wanted to know about black hole spectroscopy

Black holes vibrate, like stars, or guitar strings. The "ringdown" radiation emitted by oscillating black holes has great scientific potential. By carefully predicting the frequencies and amplitudes of black hole quasinormal modes and comparing them with gravitational-wave data from compact binary mergers we can advance our understanding of the two-body problem in general relativity, verify the predictions of the theory in the regime of strong and dynamical gravitational fields, and search for physics beyond the Standard Model or new gravitational degrees of freedom.

Following the legendary Ringdown Inside and Out meeting in Copenhagen, the community got together to write a review overviewing our knowledge of black hole spectroscopy, the programme to understand in detail the information conveyed by oscillating black holes. We summarize the state of the art in our understanding of black hole quasinormal modes in general relativity and modified gravity, their excitation, and the modeling of ringdown waveforms. We also review the status of LIGO-Virgo-KAGRA ringdown observations, data analysis techniques, and the bright prospects of the field in the era of LISA and next-generation ground-based gravitational-wave detectors. The paper is now on the arxiv!