High efficiency of collisional Penrose process requires heavy particle production

TL;DR

This paper analyzes the energy extraction efficiency of high-energy particle collisions near extremal Kerr black holes, showing that producing very massive particles can significantly increase efficiency, indicating heavy particle creation.

Contribution

It provides an analytical demonstration that producing heavy particles in the collisional Penrose process can greatly enhance energy extraction efficiency near black holes.

Findings

Efficiency bounded by ~2.19 for equal-mass particles

Efficiency increases to ~13.9 with heavy particle production

High efficiency suggests the creation of heavy particles in such collisions

Abstract

The center-of-mass energy of two particles can become arbitrarily large if they collide near the event horizon of an extremal Kerr black hole, which is called the Ba$\rm \tilde n$ados-Silk-West (BSW) effect. We consider such a high-energy collision of two particles which started from infinity and follow geodesics in the equatorial plane and investigate the energy extraction from such a high-energy particle collision and the production of particles in the equatorial plane. We analytically show that, on the one hand, if the produced particles are as massive as the colliding particles, the energy-extraction efficiency is bounded by $2.19$ approximately. On the other hand, if a very massive particle is to be produced as a result of the high-energy collision, which has negative energy and necessarily falls into the black hole, the upper limit of the energy-extraction efficiency is increased to $(2+\sqrt{3})^2 \simeq 13.9$. Thus, higher efficiency of the energy extraction, which is typically as large as 10, provides strong evidence for the production of a heavy particle.