Black holes as particle accelerators: a brief review

TL;DR

This review discusses how near-extremal Kerr black holes can act as natural particle accelerators, potentially reaching arbitrarily high energies, and explores the universality and physical limitations of this phenomenon.

Contribution

It provides a pedagogical overview of particle acceleration mechanisms near black holes, emphasizing their robustness and universality across different black hole types.

Findings

Particle acceleration can reach arbitrarily high energies near near-extremal Kerr black holes.

The maximum energy is limited by physical effects such as gravitational backreaction.

The phenomenon is likely universal for general near-extremal black holes.

Abstract

Rapidly rotating Kerr black holes can accelerate particles to arbitrarily high energy if the angular momentum of the particle is fine-tuned to some critical value. This phenomenon is robust as it is founded on the basic properties of geodesic orbits around a near-extremal Kerr black hole. On the other hand, the maximum energy of the acceleration is subjected to several physical effects. There is convincing evidence that the particle acceleration to arbitrarily high energy is one of the universal properties of general near-extremal black holes. We also discuss gravitational particle acceleration in more general context. This article is intended to provide a pedagogical introduction to and a brief overview of this topic for non-specialists.