Ultra-high-energy head-on collisions without horizons or naked singulrities: general approach

TL;DR

This paper explores a general, model-independent approach to achieving ultra-high-energy particle collisions near regions resembling black hole horizons, without the formation of horizons or naked singularities, expanding understanding of energetic astrophysical phenomena.

Contribution

It introduces a universal framework showing how unbounded collision energies can occur near extremal black hole-like metrics without actual horizon formation.

Findings

Unbound center-of-mass energy can be achieved in head-on collisions near the would-be horizon.

Energy measured at infinity can also become unbounded.

The mechanism applies to both particles and self-gravitating shells.

Abstract

Recently, alternatives to the Ba\~nados, Silk and West (BSW) effect were proposed which are (i) due to the existence of naked singularities instead of the horizon, (ii) require neither horizon nor naked singularity. We reveal the main features of such alternatives in a model-independent way. The metric should be close to that of the extremal black hole but the horizon should not form. Then, one can gain unbound the energy E_{c.m.} in the centre of mass frame due to head-on collision of particles near the would-be horizon. The energy measured at infinity can also be unbound. If instead of particles self-gravitating shells collide, the underlying reason leading to unbound E_{c.m.} is the same.