Symmetries of asymptotically flat electrovacuum spacetimes and radiation

TL;DR

This paper investigates the symmetries of asymptotically flat electrovacuum spacetimes with radiation, identifying the only permissible symmetries and deriving new formulas for mass and news functions in these contexts.

Contribution

It classifies the allowable symmetries in such spacetimes and provides new explicit forms for gravitational and electromagnetic news functions and mass aspects.

Findings

Only translational and boost symmetries are allowed under specified conditions.

Boost-rotation symmetric spacetimes are radiative and describe accelerated charged particles or black holes.

New expressions for mass and news functions in boost-rotation symmetric spacetimes are derived.

Abstract

Symmetries compatible with asymptotic flatness and admitting gravitational and electromagnetic radiation are studied by using the Bondi-Sachs-van der Burg formalism. It is shown that in axially symmetric electrovacuum spacetimes in which at least locally a smooth null infinity in the sense of Penrose exists, the only second allowable symmetry is either the translational symmetry or the boost symmetry. Translationally invariant spacetimes with in general a straight "cosmic string" along the axis of symmetry are non-radiative although they can have a non-vanishing news function. The boost-rotation symmetric spacetimes are radiative. They describe "uniformly accelerated charged particles" or black holes which in general may also be rotating - the axial and an additional Killing vector are not assumed to be hypersurface orthogonal. The general functional forms of both gravitational and electromagnetic news functions, and of the mass aspect and total mass of asymptotically flat boost-rotation symmetric spacetimes at null infinity are obtained. The expressions for the mass are new even in the case of vacuum boost-rotation symmetric spacetimes with hypersurface orthogonal Killing vectors. In Appendices some errors appearing in previous works are corrected.