**Publication date:** Jun 2018

**Abstract:**

Radiation reaction acting on a charged particle moving at a stable

circular orbit of a magnetized black hole (BH) can lead to the shift of

the orbital radius outward from the BH. The effect causes an increase of

the energy and angular momentum of the particle measured by an observer

at rest at infinity. In this paper, we show that „widening“ of such

orbits is independent of the field configuration, but it appears only in

the cases with the external Lorentz force acting outward from the BH.

This condition corresponds to qLB > 0, where q and L are the charge

and angular momentum of the particle, and B is intensity of the external

magnetic field. As examples of the orbital widening, we consider two

scenarios with an external homogeneous magnetic field and a magnetic

dipole field generated by a current loop around a Schwarzschild BH. We

show that the orbital widening is accompanied by quasi-harmonic

oscillations of the particle, which are considerably large in the

magnetic dipole fields. We also estimate the timescales of orbital

widening, from which it follows that the effect can be relevant in the

vicinity of stellar-mass BHs.

**Authors:**

Tursunov, A. A.; Kološ, M.; Stuchlík, Z.;