Testing general relativity with the ringdown of gravitational-wave observations

Gravitational waves provide a unique opportunity to test gravity and probe the nature of astrophysical sources. With hundreds of binary coalescences detected by LIGO and Virgo, general relativity continues to stand as a successful theory of gravity.

The loudest event to date, GW250114, offered a direct probe of the remnant’s Kerr nature by constraining multiple ringdown modes. In contrast, the second loudest signal, GW230814, exhibits a ringdown damping time shorter than predicted by general relativity.

Simulations indicate that such deviations can arise from missing physics in waveform models or noise artefacts, suggesting no evidence for a breakdown of general relativity. In this talk, I will present analyses of recently observed gravitational-wave signals and discuss the prospects for testing fundamental physics with next-generation detectors.