Black Hole Spectroscopy for Astrophysical Ringdowns: Imprints of Binary Dynamics*

What do astrophysical black hole ringdowns look like? Our new analysis of numerical relativity simulations of precessing binary black hole coalescences shows that, in some highly precessing systems, the (l,m) = (2,1) or even (2,0) quasinormal modes can be just as important as the (2,2). This result challenges traditional models implemented in ringdown data analysis, which have almost always assumed that the (l,m) = (2,2) quasinormal modes dominate observed ringdown signals. Our recent analysis of the LIGO-Virgo signal GW190521 has already shown hints of precessional imprints in the ringdown. Knowing that precession can be associated with distinctly different ringdowns from those of non-precessing systems begs the question of whether orbital eccentricity can also leave equally significant ringdown imprints. We speculate that the ringdown could even be used to break the degeneracy between eccentricity and precession in the future.