Magnetized Black Holes: Ionized Keplerian Disks and Acceleration of Ultra-High Energy Particles ^†

Properties of charged particle motion in the field of magnetized black holes (BHs) imply four possible regimes of behavior of ionized Keplerian disks: survival in regular epicyclic motion, transformation into chaotic toroidal state, destruction due to fall into the BHs, destruction due to escape along magnetic field lines (escape to infinity for disks orbiting Kerr BHs). The regime of the epicyclic motion influenced by very weak magnetic fields can be related to the observed high-frequency quasiperiodic oscillations. In the case of very strong magnetic fields particles escaping to infinity could form UHECR due to extremely efficient magnetic Penrose process – protons with energy $E>{10}^{21}$ eV can be accelerated by supermassive black holes with $M\sim {10}^{10}{\mathrm{M}}_{\odot }$ immersed in magnetic field with $B\sim {10}^4$ Gs.