Source multipoles and energy-momentum tensors for spinning black holes and other compact objects in arbitrary dimensions

TL;DR

This paper develops a general formalism in momentum space to derive energy-momentum tensors for spinning black holes and compact objects in arbitrary dimensions, enabling the analysis of their multipolar structures and matter sources.

Contribution

It introduces a novel method to directly obtain the multipolar structure of black hole solutions from their energy-momentum tensors in any dimension.

Findings

Derived the full multipolar structure of Kerr and Myers-Perry black holes.

Identified recurrence relations for multipole expansion in arbitrary dimensions.

Resummed the energy-momentum tensor at all orders in angular momentum.

Abstract

Working in momentum space and at linear order in the gravitational coupling, we derive the most general class of energy-momentum tensors associated with a given multipolar structure of the spacetime in arbitrary dimensions, and built out of a mass and an angular momentum, at any order in the spin expansion. In this formalism, we are able to derive directly the full multipolar structure of any solution from the multipole expansion of the energy-momentum tensor, in complete analogy to Newtonian gravity. In particular, we identify the recurrence relations that allow obtaining the multipolar structure of the Kerr and the Myers-Perry black hole solutions, defining source multipoles in a General Relativity context for the first time. For these solutions, we are able to resum the energy-momentum tensor in momentum space at all orders in the angular momentum, and compute its real-space version. In the Kerr case we exactly obtain the matter source found by Israel, namely an equatorial, pressureless thin disk rotating at superluminal speed. For Myers-Perry in five dimensions, the matter distribution is a three-ellipsoid in four spatial dimensions with nontrivial stresses. Remarkably, for any dimensions, the matter configuration is a lower-dimensional distribution which has the same singularity structure as the fully non-linear black-hole solution. Our formalism underscores the advantage of working in momentum space to generate nontrivial matter sources for non-linear spacetimes, and could be used to construct regular non-exotic matter configurations that source spinning black hole solutions or horizonless compact objects with the same multipolar structure as black holes.