High energy collision of particles in the magnetic field far from black holes

TL;DR

This paper investigates how strong magnetic fields enable high-energy particle collisions far from black holes, extending known effects from the ergoregion to regions near rotating stars.

Contribution

It demonstrates that large collision energies can be achieved in flat regions due to magnetic fields, not just near black holes or in ergoregions.

Findings

High collision energies are possible far from black holes with strong magnetic fields.

Large E_{c.m.} can occur even outside the ergoregion in flat spacetime.

The effect also applies to rotating star metrics.

Abstract

We consider collision of two particles in the axially symmetric black hole metric in the magnetic field. If the value of the angular momentum |L| of one particles grows unbound (but its Killing energy remains fixed) one can achieve unbound energy in the center of mass frame E_{c.m.} In the absence of the magnetic field, collision of this kind is known to happen in the ergoregion. However, if the magnetic field strength B is also large, with the ratio |L|/B being finite, large E_{c.m.} can be achieved even far from a black hole, in the almost flat region. Such an effect also occurs in the metric of a rotating star.