The irreducible mass and the horizon area of LIGO's black holes

TL;DR

This paper calculates the irreducible masses of LIGO's stellar-mass black holes, re-parametrizes their energy contributions, and ranks mergers by irreversibility to inform tests of General Relativity and horizon area evolution.

Contribution

It introduces a method to extract irreducible and rotational energy components from gravitational-wave data and ranks black-hole mergers by irreversibility, advancing understanding of black hole horizon dynamics.

Findings

Re-parametrized posterior distributions highlighting irreducible mass.

Ranked black-hole mergers by irreversibility using the area law.

Estimated the rate of horizon area increase from observed mergers.

Abstract

The mass of a Kerr black hole can be separated into irreducible and rotational components -the former is a lower limit to the energy that cannot be possibly extracted from the event horizon and is related to its area. Here we compute the irreducible masses of the stellar-mass black holes observed by gravitational-wave interferometers LIGO and Virgo. Using single-event data, we present a re-parametrization of the posterior distribution that explicitly highlights the irreducible and rotational contributions to the total energy. We exploit the area law to rank the black-hole mergers observed to date according to their irreversibility, thus providing a guide to selecting events for targeted tests of General Relativity. Using population fits, we compute the rate by which the total area of black-hole horizons increases due to the observable mergers.