Pure and gravitational radiation

TL;DR

This paper adapts the asymptotic analysis of vacuum fields to pure radiation fields, revealing how mass loss is due to combined pure and gravitational radiation, and identifies a unique solution in axisymmetric cases.

Contribution

It introduces a normalization for radiation null vectors and characterizes the mass loss as a superposition of pure and gravitational radiation components.

Findings

Mass loss at null infinity is due to superposed pure and gravitational radiation.

Identifies the Kinnersley photon rocket as the unique axisymmetric pure radiation solution without gravitational radiation.

Provides a natural normalization for the radiation null vector.

Abstract

The well-known treatment of asymptotically flat vacuum fields is adapted to pure radiation fields. In this approach we find a natural normalization of the radiation null vector. The energy balance at null infinity shows that the mass loss results from a linear superposition of the pure and the gravitational radiation parts. By transformation to Bondi-Sachs coordinates the Kinnersley photon rocket is found to be the only axisymmetric Robinson-Trautman pure radiation solution without gravitational radiation.