Effect of a weak electromagnetic field on particle acceleration by a rotating black hole

Abstract

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.

Acceleration of the charged particles due to chaotic scattering in the combined black hole gravitational field and asymptotically uniform magnetic field

“…where ρ 0 denotes the particle initial position (its radial coordinate), and u φ is charged particle angular velocity (39) given by the relation…”

“…The study of the charged particles 'kicked' from the innermost stable circular orbit (ISCO) in the equatorial plane and hence escaping to infinity along the axis of symmetry has been treated in [33] -because the charged particle motion in the vicinity of a black hole immersed into magnetic field is chaotic, the resulting final ejection velocity does not depend continuously on the initial conditions [28]. It has been demonstrated that collisions of particles in the vicinity of black holes could be enhanced by the external magnetic fields [39][40][41][42][43], but these processes can be observationally efficient especially in the field of Kerr naked singularities [44]. The relation of the quasi-circular equatorial motion of charged test particles around black holes immersed in the magnetic field to the high-frequency quasiperiod oscillations observed in some microquasars has been demonstrated in [29].…”

Rotating Ayón-Beato-García black hole as a particle accelerator

“…There-fore, the CM energy of collision expected to depend both on spin and charge. The BSW scenario is generalized to charged BHs [5], the Kerr-Newman family of BHs [6] and general rotating BHs [7]. It is shown that, for a nearextremal charged BH, there always exists a finite upper bound for CM energy, which decreases with the increase of the charge Q.…”

Motion of charged particles around a weakly magnetized rotating black hole

“…Although this is a simplified problem, the dynamics are still nonintegrable due to the lack of a third constant of motion (the Carter constant) in the presence of a magnetic field. If we focus on equatorial motion, a semi-analytical approach is possible [10][11][12], but a general orbit requires numerics [13][14][15][16][17]. More specifically, we consider the motion of a charged particle kicked out from the equatorial plane, and investigate the conditions under which such a particle can escape to infinity.…”