Negative Horizon Mass for Rotating Black Holes

TL;DR

This paper explores the unusual properties of charged rotating black holes in higher-dimensional Einstein-Maxwell-Chern-Simons theory, revealing phenomena like negative horizon mass, counterrotation, and non-uniqueness in black hole characterization.

Contribution

It introduces the concept of negative horizon mass and demonstrates the existence of black holes with counterrotating features and non-uniqueness in higher dimensions.

Findings

Black holes can have negative horizon mass despite positive total mass.

Existence of counterrotating solutions with opposite signs of horizon angular velocity and angular momentum.

Black holes can have vanishing horizon angular velocity with finite angular momentum, and vice versa.

Abstract

Charged rotating black holes of Einstein-Maxwell-Chern-Simons theory in odd dimensions, $D \ge 5$, may possess a negative horizon mass, while their total mass is positive. This surprising feature is related to the existence of counterrotating solutions, where the horizon angular velocity $\Omega$ and the angular momentum $J$ possess opposite signs. Black holes may further possess vanishing horizon angular velocity while they have finite angular momentum, or they may possess finite horizon angular velocity while their angular momentum vanishes. In D=9 even non-static black holes with $\Omega=J=0$ appear. Charged rotating black holes with vanishing gyromagnetic ratio exist, and black holes need no longer be uniquely characterized by their global charges.