Non-extremal Kerr black holes as particle accelerators

TL;DR

This paper investigates particle collisions near non-extremal Kerr black holes, demonstrating that while infinite energies are impossible at the outer horizon, ultraenergetic collisions can occur at the inner horizon regardless of the black hole's spin.

Contribution

It provides a general proof that infinite collision energies cannot occur at the outer horizon of non-extremal Kerr black holes and shows that ultraenergetic collisions are possible at the inner horizon.

Findings

No arbitrarily high energy collisions at the outer horizon.

Ultraenergetic collisions possible at the inner horizon.

Results apply to Kerr black holes with any spin parameter.

Abstract

It has been shown that extremal Kerr black holes can be used as particle accelerators and arbitrarily high energy may be obtained near the event horizon. We study particle collisions near the event horizon (outer horizon) and Cauchy horizon (inner horizon) of a non-extremal Kerr black hole. Firstly, we provide a general proof showing that particles cannot collide with arbitrarily high energies at the outter horizon. Secondly, we show that ultraenergetic collisions can occur near the inner horizon of a Kerr black hole with any spin parameter $a$.