Second-Order Black Hole Perturbations: A Computer Algebra Approach, I - The Schwarzschild Spacetime

TL;DR

This paper derives second-order perturbations of a Schwarzschild black hole using computer algebra, confirming previous results and providing tools for more general analyses.

Contribution

It introduces a direct computer algebra method for second-order black hole perturbations, including new routines for the GRTensorII package.

Findings

Confirmed earlier second-order perturbation results

Demonstrated a direct solution method for linear Schwarzschild problems

Provided publicly available routines for general perturbation analysis

Abstract

This article outlines our derivation of the second order perturbations to a Schwarzschild black hole, highlighting our use of, and necessary reliance on, computer algebra. The particular perturbation scenario that is presented here is the case of the linear quadrapole seeding the second order quadrapole. This problem amounts to finding the second order Zerilli wave equation, and in particular the effective source term due to the linear quadrapole. With one minor exception, our calculations confirm the earlier findings of Gleiser, et.al. On route to these results we also illustrate that, with the aid of computer algebra, the linear Schwarzschild problem can be solved in a very direct manner (i.e., without resorting to the usual function transformations), and it is this ``direct method'' that drives the higher order perturbation analysis. The calculations were performed using the GRTensorII computer algebra package, running on the Maple V platform, along with several new Maple routines that we have written specifically for these types of problems. Although we have chosen to consider only the ``quadrapole-quadrapole'' calculation in this article, the GRTensor environment, with the inclusion of these new routines, would allow this analysis to be repeated for a far more general problem. These routines, along with Maple worksheets that reproduce our calculations, are publicly available at the GRTensor website: www.astro.queensu.ca/~grtensor . The interested reader is invited to download and use them to reproduce our results and experiment.