Exploring black holes as particle accelerators: hoop-radius, target particles and escaping conditions

Abstract

The possibility that rotating black holes could be natural particle accelerators has been subject of intense debate. While it appears that for extremal Kerr black holes arbitrarily high center of mass energies could be achieved, several works pointed out that both theoretical as well as astrophysical arguments would severely dampen the attainable energies. In this work we study particle collisions near Kerr black holes, by reviewing and extending the so far proposed scenarios. Most noticeably, we shall focus on the recently advanced target particle scenarios which were claimed to reach arbitrarily high energies even for Schwarzschild black holes. By implementing the hoop conjecture we show that these scenarios involving near-horizon target particles are in principle able to attain, sub-Planckian, but still ultra-high center of mass energies of the order of $10^{23}-10^{25}$ eV even for non-extremal Kerr black holes. Furthermore, analysing the properties of particles produced in such collisions, we find that photons can escape to infinity. However, their energy is only of the order of the energy of the colliding particles and hence relatively low, which is the same conclusion previously reached in the literature about the original Bañados--Silk--West process. This finding points towards a general limitation of collisional Penrose processes, at least for what concerns their primary products.

Improved and extended version of the original article, now including a discussion of the escape conditions for the particles produced in a collisional Penrose processes

References in corpus (12)

• Measurement of the cosmic-ray energy spectrum above $2.5\times 10^{18}$ eV using the Pierre Auger Observatory
• Charged Spinning Black Holes as Particle Accelerators
• Acceleration of particles by nonrotating charged black holes
• Collisional Penrose process near the horizon of extreme Kerr black holes
• Can binary mergers produce maximally spinning black holes?
• Kerr-de Sitter and Kerr-anti-de Sitter black holes as accelerators for spinning particles
• Universality of BSW mechanism for spinning particles
• Further evidence for the non-existence of a unified hoop conjecture
• Special case of the Bañados-Silk-West effect
• Schwarzschild black hole surrounded by quintessential matter field as an accelerator for spinning particles
• Upper bound on the center-of-mass energy of the collisional Penrose process
• Timescale for trans-Planckian collisions in Kerr spacetime

Cited by in corpus (6)

• Bañados-Silk-West effect with finite forces near different types of horizons: general classification of scenarios
• Relativistic deformed kinematics: from flat to curved spacetimes
• BSW phenomenon for near-fine-tuned particles with external force: general classification of scenarios
• On the Kalb-Ramond modified Lorentz violating hairy black holes and Thorne's hoop conjecture
• Signatures of particle collisions near extreme black holes
• Near-Horizon Collisions around Near-Extremal Black Holes