Sliding Rings and Spinning Holes

TL;DR

This paper constructs smooth supergravity solutions for BPS black rings with embedded black holes, revealing how angular momentum and entropy behave during mergers, and identifying conditions for thermodynamically reversible mergers.

Contribution

It introduces new supergravity solutions describing black ring and black hole configurations with arbitrary separation, and analyzes their merger dynamics and thermodynamic properties.

Findings

Black ring entropy remains constant during black hole movement.

Merging a black ring with a black hole increases the ring's angular momentum.

Certain mergers are thermodynamically reversible.

Abstract

We construct smooth supergravity solutions describing a BPS black ring with a BPS black hole centered at an arbitrary distance above the ring. We find that as one moves the black hole the entropy of the ring remains constant, but the angular momentum coming from the supergravity fluxes changes. Our solutions also show that in order to merge a BPS black ring with a BPS black hole one has to increase one of the angular momenta of the ring, and that the result of the merger is always a BMPV black hole. We also find a class of mergers that are thermodynamically reversible, and comment on their physics.