Spin and energy evolution equations for a wide class of extended bodies

TL;DR

This paper derives comprehensive evolution equations for the spin and energy of arbitrarily shaped, strongly self-gravitating bodies in a relativistic setting, extending previous weak-field results to more general cases.

Contribution

It provides a surface integral derivation of spin and energy evolution equations applicable to strongly self-gravitating bodies, including all multipole effects, broadening their validity.

Findings

Derived equations match weak-field results for self-gravitating bodies.

Extended the applicability of evolution equations to strongly self-gravitating bodies.

Included all mass and current multipole effects in the derivation.

Abstract

We give a surface integral derivation of the leading-order evolution equations for the spin and energy of a relativistic body interacting with other bodies in the post-Newtonian expansion scheme. The bodies can be arbitrarily shaped and can be strongly self-gravitating. The effects of all mass and current multipoles are taken into account. As part of the computation one of the 2PN potentials parametrizing the metric is obtained. The formulae obtained here for spin and energy evolution coincide with those obtained by Damour, Soffel and Xu for the case of weakly self-gravitating bodies. By combining an Einstein-Infeld-Hoffman-type surface integral approach with multipolar expansions we extend the domain of validity of these evolution equations to a wide class of strongly self-gravitating bodies. This paper completes in a self-contained way a previous work by Racine and Flanagan on translational equations of motion for compact objects.