Degenerate Black Rings in $D=5$ Minimal Supergravity

TL;DR

This paper discovers new extremal degenerate black rings in five-dimensional supergravity with specific charge-angular momentum relations, revealing two black hole branches and a rotating soliton, with implications for black hole uniqueness and horizon geometry.

Contribution

It introduces the existence of degenerate black rings with specific charge-angular momentum relations in 5D supergravity, expanding the known solutions and their near-horizon geometries.

Findings

Two branches of extremal rotating black holes exist, merging into a degenerate black ring.

The near-horizon geometry is locally AdS3×S2, with the S3 fiber collapsing.

A rotating soliton with smaller mass than the black ring is also found.

Abstract

We consider both gauged and ungauged minimal supergravities in five dimensions and analyse the charged rotating solutions with two equal angular momenta $J$. When the electric charge $Q\sim J^{2/3}$ with some specific coefficient, we find new extremal black objects emerge that are asymptotic to either Minkowski or global AdS spacetimes and can be best described as degenerate black rings. Their near-horizon geometry is locally AdS$_3\times S^2$, where the periodic $U(1)$ fibre coordinate in $S^3$ untwists and collapses to be the degenerate part of the AdS$_3$ horizon. It turns out that there are two branches of extremal rotating black holes, starting as the extremal RN black holes of the same mass, but opposite charges. With the increasing of the angular momentum, they will join to become the same degenerate black ring, where the Gibbs free energies however are not continuous at the joining. For the same $Q(J)$ relation, we find that there is in addition a rotating soliton whose mass is smaller than the degenerate black ring.