Why black hole ringdowns hide their most interesting frequency crossings

Black hole quasinormal modes can undergo avoided crossings — events where two mode frequencies approach each other, their amplitudes surge, and they oscillate nearly out of phase, producing a distinctive interference signature in the ringdown signal. Using Bayesian inference with three different waveform models, this study tests how well current gravitational-wave spectroscopy could recover those frequencies. Separating the individual modes proves difficult under realistic conditions, but the collective waveform distortion from the crossing may still be identified if those modes dominate the signal and slower-decaying background modes can be subtracted away.