Energy conservation for dynamical black holes

TL;DR

This paper develops a comprehensive energy conservation law for dynamical black holes, relating mass-energy changes to infalling matter and gravitational radiation, and introduces new integral forms and an effective energy tensor.

Contribution

It presents a new, regular integral and differential form of the first law of black-hole dynamics for evolving black holes, including an effective gravitational-radiation energy tensor.

Findings

Derived a regular energy conservation law for dynamical black holes.

Introduced an effective gravitational-radiation energy tensor.

Formulated a Gibbs-like equation for black hole energy flux.

Abstract

An energy conservation law is described, expressing the increase in mass-energy of a general black hole in terms of the energy densities of the infalling matter and gravitational radiation. For a growing black hole, this first law of black-hole dynamics is equivalent to an equation of Ashtekar & Krishnan, but the new integral and differential forms are regular in the limit where the black hole ceases to grow. An effective gravitational-radiation energy tensor is obtained, providing measures of both ingoing and outgoing, transverse and longitudinal gravitational radiation on and near a black hole. Corresponding energy-tensor forms of the first law involve a preferred time vector which plays the role for dynamical black holes which the stationary Killing vector plays for stationary black holes. Identifying an energy flux, vanishing if and only if the horizon is null, allows a division into energy-supply and work terms, as in the first law of thermodynamics. The energy supply can be expressed in terms of area increase and a newly defined surface gravity, yielding a Gibbs-like equation, with a similar form to the so-called first law for stationary black holes.