Unbound geodesics from the ergosphere and potential observability of debris from ultrahigh energy particle collisions

Abstract

Particle collisions in black hole ergoregions may result in extremely high center of mass energies that could probe new physics if escape to infinity were possible. Here we show that some geodesics at high inclinations to the equatorial plane may be unbound. Hence a finite flux of annihilation debris is able to escape, especially in the case of near-extremal Kerr black holes and if the Penrose process plays a role. For a class of Penrose processes, we show that the Wald inequalities are satisfied, allowing the Penrose process to have a key role in high energy ejection. Hence the possibility of observing new physics effects from a black hole accelerator at unprecedentedly high particle collision energies remains a tantalizing, if futuristic, experimental vision.

Unbounded energies of debris from head-on particle collisions near black holes

“…It was shown in [6] (and confirmed by another methods in [7]) that for the Reissner-Nordström black hole the upper limit on the energy of debris of collision does not exist. There also some indications in the favour of unbounded E for geodesics at high inclinations to the equatorial plane of motion [8]. Significant enhancement of this energy for nonequatorial motion was found in [9].…”

Ultrahigh-Energy Debris from the Collisional Penrose Process

“…Very few off-equatorial calculations of the Penrose process have been performed in the past, mainly due to computational difficulties. The results reported here, together with recent studies of the off-equatorial collisional Penrose process [23,24], suggest that surprises may be in store, and a generalization of our calculations to the off-equatorial case is urgently needed.…”

Kinematics of two-particle scattering in black hole backgrounds

“…This unboundedness is independent of the Thorne bound [5], [6] (a bound on the energy of the particle per unit Kerr parameter [7]). These effects hold true for various astrophysical scenarios like in the presence of the magnetic field [9], [10] and in the context of observability of high energy particles in astrophysical black hole backgrounds [11]- [15]. It is by now established that the effect of the unboundedness in the center-of-mass energy in certain kinematical domains are a universal property of classical particle kinematics in the background of asymptotically flat black holes [2], [16].…”

“…For L (1) = L (2) = 0 (radial motion), s 12 reduces to the expression given in [2]. If we take the extremal limit (f ′ → 0) after taking the horizon limit (f → 0) six scalars are found to be same as (15) but with r H = M = Q.…”