1202.4859 (Takahisa Igata et al.)

Effect of a Weak Electromagnetic Field on Particle Acceleration by a
Rotating Black Hole    [PDF]

Takahisa Igata, Tomohiro Harada, Masashi Kimura

We study high energy charged particle collisions near the horizon in an
electromagnetic field around a rotating black hole and reveal the condition of
the fine-tuning to obtain arbitrarily large center-of-mass (CM) energy. We
demonstrate that the CM energy can be arbitrarily large as the uniformly
magnetized rotating black hole arbitrarily approaches maximal rotation under
the situation that a charged particle plunges from the innermost stable
circular orbit (ISCO) and collides with another particle near the horizon.
Recently, Frolov [Phys. Rev. D 85, 024020 (2012)] proposed that the CM energy
can be arbitrarily high if the magnetic field is arbitrarily strong, when a
particle collides with a charged particle orbiting the ISCO with finite energy
near the horizon of a uniformly magnetized Schwarzschild black hole. We show
that the charged particle orbiting the ISCO around a spinning black hole needs
arbitrarily high energy in the strong field limit. This suggests that Frolov's
process is unstable against the black hole spin. Nevertheless, we see that
magnetic fields may substantially promote the capability of rotating black
holes as particle accelerators in astrophysical situations.

View original: http://arxiv.org/abs/1202.4859