Gravitational Footprints of Black Holes and Their Microstate Geometries

TL;DR

This paper constructs non-supersymmetric extremal black holes and microstate geometries in four dimensions, analyzing their gravitational multipole structures to understand deviations from Kerr black holes caused by horizon-scale physics.

Contribution

It introduces a family of non-supersymmetric extremal black holes and microstate geometries with astrophysical relevance, and computes their gravitational multipoles to compare with Kerr solutions.

Findings

Black hole multipoles depend non-trivially on charge-to-mass ratio.

Microstate geometries share multipoles with black holes, with small deviations.

Deviations from Kerr are influenced by microstructure scale.

Abstract

We construct a family of non-supersymmetric extremal black holes and their horizonless microstate geometries in four dimensions. The black holes can have finite angular momentum and an arbitrary charge-to-mass ratio, unlike their supersymmetric cousins. These features make them and their microstate geometries astrophysically relevant. Thus, they provide interesting prototypes to study deviations from Kerr solutions caused by new horizon-scale physics. In this paper, we compute the gravitational multipole structure of these solutions and compare them to Kerr black holes. The multipoles of the black hole differ significantly from Kerr as they depend non-trivially on the charge-to-mass ratio. The horizonless microstate geometries have the same multipoles as their corresponding black hole, with small deviations set by the scale of their microstructure.