The Collisional Penrose Process

TL;DR

This paper reviews the collisional Penrose process, a mechanism where particle collisions near a rotating black hole's ergosphere can extract energy, with potential applications in dark matter annihilation enhancement.

Contribution

It highlights a specific astrophysical application of the collisional Penrose process in increasing dark matter annihilation near supermassive black holes.

Findings

Particles can achieve arbitrarily high energies in collisions near extremal black holes.

Negative energy particles within the ergosphere can extract black hole mass and angular momentum.

Potential to probe high-energy physics and general relativity through astrophysical observations.

Abstract

Shortly after the discovery of the Kerr metric in 1963, it was realized that a region existed outside of the black hole's event horizon where no time-like observer could remain stationary. In 1969, Roger Penrose showed that particles within this ergosphere region could possess negative energy, as measured by an observer at infinity. When captured by the horizon, these negative energy particles essentially extract mass and angular momentum from the black hole. While the decay of a single particle within the ergosphere is not a particularly efficient means of energy extraction, the "collision" of multiple particles can reach arbitrarily high center-of-mass energy in the limit of extremal black hole spin. The resulting particles can escape with high efficiency, potentially serving as a probe of high-energy particle physics as well as general relativity. In this paper, we briefly review the history of the field and highlight a specific astrophysical application of the collisional Penrose process: the potential to enhance annihilation of dark matter particles in the vicinity of a supermassive black hole.