On the final spin from the coalescence of two black holes

TL;DR

This paper presents an analytic formula to accurately predict the final spin of a black hole resulting from the merger of two black holes, based on numerical relativity data and applicable to various initial conditions.

Contribution

It introduces a new compact analytic formula for the final black hole spin that models generic initial spins and mass ratios, validated against numerical simulations.

Findings

High agreement with existing numerical relativity data

Applicable to generic initial spin configurations and mass ratios

Provides a basis for improved modeling of black hole mergers

Abstract

We provide a compact analytic formula to compute the spin of the black hole produced by the coalescence of two black holes. The expression, which uses an analytic fit of numerical-relativity data and relies on four assumptions, aims at modelling generic initial spin configurations and mass ratios. A comparison with numerical-relativity simulations already shows very accurate agreements with all of the numerical data available to date, but we also suggest a number of ways in which our predictions can be further improved.