Ultraspinning instability of rotating black holes

TL;DR

This paper investigates the ultraspinning instability of rapidly rotating higher-dimensional black holes, establishing its presence across various dimensions, analyzing boundary conditions, and discovering related Gregory-Laflamme instabilities, thereby advancing understanding of black hole phase transitions.

Contribution

The study confirms ultraspinning instabilities in multiple dimensions, details boundary conditions preserving thermodynamic properties, and identifies new Gregory-Laflamme instabilities in rotating black strings and branes.

Findings

Ultraspinning instability exists in d=6,10,11 dimensions.

Boundary conditions preserve angular velocity and temperature.

New Gregory-Laflamme instabilities found at critical rotation.

Abstract

Rapidly rotating Myers-Perry black holes in d>5 dimensions were conjectured to be unstable by Emparan and Myers. In a previous publication, we found numerically the onset of the axisymmetric ultraspinning instability in the singly-spinning Myers-Perry black hole in d=7,8,9. This threshold signals also a bifurcation to new branches of axisymmetric solutions with pinched horizons that are conjectured to connect to the black ring, black Saturn and other families in the phase diagram of stationary solutions. We firmly establish that this instability is also present in d=6 and in d=10,11. The boundary conditions of the perturbations are discussed in detail for the first time and we prove that they preserve the angular velocity and temperature of the original Myers-Perry black hole. This property is fundamental to establish a thermodynamic necessary condition for the existence of this instability in general rotating backgrounds. We also prove a previous claim that the ultraspinning modes cannot be pure gauge modes. Finally we find new ultraspinning Gregory-Laflamme instabilities of rotating black strings and branes that appear exactly at the critical rotation predicted by the aforementioned thermodynamic criterium. The latter is a refinement of the Gubser-Mitra conjecture.