Impact of Entropy on Black Hole Astrophysics

As an irreversible process, mergers between two black holes will increase the entropy of the universe. By imposing thermodynamical constraints, we showcase BRAHMA (BinaRy blAck Holes Merger entropy Analysis) -- a novel framework to infer the properties and astrophysical implications of binary black hole mergers in LIGO-Virgo-KAGRA (LVK). We apply the framework to 10 of the heaviest binary black hole merger events reported by LVK Collaboration and perform a systematic investigation on the consistency between phenomenological waveform and ringdown models. In doing so, we obtain new strong astrophysical insights into the origins of some of these heavy black holes. We demonstrate that using the BRAHMA framework would be particularly useful for intermediate binary black hole merger population in future gravitational wave detection.