Nonrotating black hole in a post-Newtonian tidal environment

TL;DR

This paper models a nonrotating black hole within a weak, post-Newtonian external gravitational field, deriving its motion, tidal deformation, and energy absorption, applicable to various astrophysical scenarios.

Contribution

It develops a general framework for matching black hole and post-Newtonian metrics to study tidal effects without specific environmental assumptions.

Findings

Derived equations of motion and tidal fields for the black hole.

Analyzed the deformed event horizon geometry.

Calculated tidal heating and mass accretion rate.

Abstract

We examine the motion and tidal dynamics of a nonrotating black hole placed within a post-Newtonian external spacetime. The tidal perturbation created by the external environment is treated as a small perturbation. At a large distance from the black hole, the gravitational field of the external distribution of matter is assumed to be sufficiently weak to be adequately described by the (first) post-Newtonian approximation to general relativity. There, the black hole is treated as a monopole contribution to the total gravitational field. There exists an overlap in the domains of validity of each description, and the black-hole and post-Newtonian metrics are matched in the overlap. The matching procedure produces the equations of motion for the black hole and the gravito-electric and gravito-magnetic tidal fields acting on the black hole. We first calculate the equations of motion and tidal fields by making no assumptions regarding the nature of the post-Newtonian environment; this could contain a continuous distribution of matter or any number of condensed bodies. We next specialize our discussion to a situation in which the black hole is a member of a post-Newtonian two-body system. As an application of our results, we examine the geometry of the deformed event horizon and calculate the tidal heating of the black hole, the rate at which it acquires mass as a result of its tidal interaction with the companion body.