Thermodynamics to infer the astrophysics of binary black hole mergers

Understand

We introduce the Merger Entropy Index ($\mathcal{I}_\mathrm{BBH}$), a new parameter to measure the efficiency of entropy transfer for any generic binary black hole merger in General Relativity.

• We find that $\mathcal{I}_\mathrm{BBH}$ is bounded between an asymptotic maximum and minimum.
• For the observed population of mergers detected by LIGO and Virgo, we find that $\mathcal{I}_\mathrm{BBH}$ is $\lesssim30\%$ of its theoretical maximum.
• By imposing the thermodynamical consistency between the pre- and post-merger states through $\mathcal{I}_\mathrm{BBH}$, we showcase BRAHMA -- a novel framework to infer the properties and astrophysical implications of gravitational-wave detections.