Multipole moments of stationary space-times

Abstract

Multipole moments are defined for stationary, asymptotically flat, source-free solutions of Einstein's equation. There arise two sets of multipole moments, the mass moments and the angular momentum moments. These quantities emerge as tensors at a point A ``at spatial infinity.'' They may be expressed as certain combinations of the derivatives at A of the norm and twist of the timelike Killing vector. In the Newtonian limit, the moments reduce to the usual multipole moments of the Newtonian potential. Some properties of these moments are derived, and, as an example, the multipole moments of the Kerr solution are discussed.