Ultra-high-energy debris from the collisional Penrose process

TL;DR

This paper demonstrates that particle collisions near rapidly rotating black holes can produce ultra-high-energy debris with efficiencies much higher than previously estimated, potentially explaining gamma rays and cosmic rays.

Contribution

It reveals that the collisional Penrose process can achieve significantly higher efficiencies in generic conditions around fast-spinning black holes, expanding the understanding of energy extraction mechanisms.

Findings

High-energy ejecta from collisions near rotating black holes

Maximum efficiency estimates around 15, higher than prior models

Potential explanation for gamma rays and ultra-high-energy cosmic rays

Abstract

Soon after the discovery of the Kerr metric, Penrose realized that superradiance can be exploited to extract energy from black holes. The original idea (involving the breakup of a single particle) yields only modest energy gains. A variant of the Penrose process consists of particle collisions in the ergoregion. The collisional Penrose process has been explored recently in the context of dark matter searches, with the conclusion that the ratio $\eta$ between the energy of post-collision particles detected at infinity and the energy of the colliding particles should be modest ($\eta \lesssim 1.5$). Schnittman has shown that these studies underestimated the maximum efficiency by about one order of magnitude (i.e., $\eta \lesssim 15$). In this work we show that particle collisions in the vicinity of rapidly rotating black holes can produce high-energy ejecta and result in high efficiencies under much more generic conditions. The astrophysical likelihood of these events deserves further scrutiny, but our study hints at the tantalizing possibility that the collisional Penrose process may power gamma rays and ultra-high-energy cosmic rays.