Construction of the second-order gravitational perturbations produced by a compact object

TL;DR

This paper develops a method to construct well-defined second-order gravitational perturbation solutions caused by a compact object orbiting a supermassive black hole, crucial for precise gravitational wave modeling.

Contribution

It resolves the divergence issues in second-order perturbation equations, enabling accurate waveform template generation for gravitational wave detectors like LISA.

Findings

Resolved divergence in second-order perturbation equations

Constructed physically meaningful solutions for point particle sources

Facilitated accurate gravitational waveform modeling

Abstract

Accurate calculation of the gradual inspiral motion in an extreme mass-ratio binary system, in which a compact-object inspirals towards a supermassive black-hole requires calculation of the interaction between the compact-object and the gravitational perturbations that it induces. These metric perturbations satisfy linear partial differential equations on a curved background spacetime induced by the supermassive black-hole. At the point particle limit the second-order perturbations equations have source terms that diverge as $r^{-4}$, where $r$ is the distance from the particle. This singular behavior renders the standard retarded solutions of these equations ill-defined. Here we resolve this problem and construct well-defined and physically meaningful solutions to these equations. We recently presented an outline of this resolution [E. Rosenthal, Phys. Rev. D 72, 121503 (2005)]. Here we provide the full details of this analysis. These second-order solutions are important for practical calculations: the planned gravitational-wave detector LISA requires preparation of waveform templates for the expected gravitational-waves. Construction of templates with desired accuracy for extreme mass-ratio binaries requires accurate calculation of the inspiral motion including the interaction with the second-order gravitational perturbations.