Pragmatic approach to gravitational radiation reaction in binary black holes

TL;DR

This paper develops a regularization method for calculating gravitational radiation reaction in binary black hole systems with small mass ratios, enabling more accurate modeling of gravitational waves for detectors.

Contribution

It introduces a zeta-function regularization scheme for summing metric perturbations around Schwarzschild black holes, improving the computation of gravitational wave templates.

Findings

Successfully regularized the metric perturbation sum.

Numerically computed first-order geodesics.

Method applicable to rotating black holes for gravitational wave detection.

Abstract

We study the relativistic orbit of binary black holes in systems with small mass ratio. The trajectory of the smaller object (another black hole or a neutron star), represented as a particle, is determined by the geodesic equation on the perturbed massive black hole spacetime. The particle itself generates the gravitational perturbations leading to a problem that needs regularization. Here we study perturbations around a Schwarzschild black hole using Moncrief's gauge invariant formalism. We decompose the perturbations into $\ell-$multipoles to show that all $\ell-$metric coefficients are $C^0$ at the location of the particle. Summing over $\ell$, to reconstruct the full metric, gives a formally divergent result. We succeed in bringing this sum to a generalized Riemann's $\zeta-$function regularization scheme and show that this is tantamount to subtract the $\ell\to\infty$ piece to each multipole. We explicitly carry out this regularization and numerically compute the first order geodesics. Application of this method to general orbits around rotating black holes would generate accurate templates for gravitational wave laser interferometric detectors.