Cosmic black holes can act as agents of particle acceleration. We study properties of a system consisting of a rotating black hole immersed in a large-scale organized magnetic field. Electrically charged particles in the immediate neighborhood of the horizon are influenced by strong gravity acting together with magnetic and induced electric components. We relax several constraints which were often imposed in previous works: the magnetic field does not have to share a common symmetry axis with the spin of the black hole but they can be inclined with respect to each other, thus violating the axial symmetry. Also, the black hole does not have to remain at rest but it can instead perform fast translational motion together with rotation. We demonstrate that the generalization brings new effects. Starting from uniform electro-vacuum fields in the curved spacetime, we find separatrices and identify magnetic neutral points forming in certain circumstances. We suggest that these structures can represent signatures of magnetic reconnection triggered by frame-dragging effects in the ergosphere. We further investigate the motion of charged particles in these black hole magnetospheres. We concentrate on the transition from the regular motion to chaos, and in this context we explore the characteristics of chaos in...

The origin of Ultra-High-Energy Cosmic Rays (UHECRs) is still an open question in Astrophysics. The scope of this thesis is the study of the termination shocks in the jets of radiogalaxies 3C 105, 3C 227, and 3C 445 as cosmic rays accelerators. We assume the diffusive shock acceleration (DSA) and that the maximum energy is determined by the escape of cosmic rays downstream of the shock due to the magnetization. We find maximum achievable energy of non-thermal electrons and protons, which appeared to be only~TeV. Therefore the reverse shocks of AGNs' jets are not the sources of UHECRs. We also implement the model, where the scattering centers for the DSA emerge from the non- resonant hybrid instabilities in plasma. We take into account the results from the numerical simulations and observations that indicate the amplification of the magnetic field by orders of magnitude, and we obtain results that qualitatively fit the simulation outcome.