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

We consider collision of two particles in the axially symmetric black hole metric in the magnetic field. If the value of the angular momentum vertical bar L vertical bar 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 vertical bar L vertical bar/ 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.