Publication date: Jan 2016
Abstract:
To test the role of large-scale magnetic fields in accretion processes,
we study the dynamics of the charged test particles in the vicinity of a
black hole immersed into an asymptotically uniform magnetic field. Using
the Hamiltonian formalism of the charged particle dynamics, we examine
chaotic scattering in the effective potential related to the black hole
gravitational field combined with the uniform magnetic field. Energy
interchange between the translational and oscillatory modes of the
charged particle dynamics provides a mechanism for charged particle
acceleration along the magnetic field lines. This energy transmutation
is an attribute of the chaotic charged particle dynamics in the combined
gravitational and magnetic fields only, the black hole rotation is not
necessary for such charged particle acceleration. The chaotic scatter
can cause a transition to the motion along the magnetic field lines with
small radius of the Larmor motion or vanishing Larmor radius, when the
speed of the particle translational motion is largest and it can be
ultra-relativistic. We discuss the consequences of the model of
ionization of test particles forming a neutral accretion disc, or heavy
ions following off-equatorial circular orbits, and we explore the fate
of heavy charged test particles after ionization where no kick of heavy
ions is assumed and only the switch-on effect of the magnetic field is
relevant. We demonstrate that acceleration and escape of the ionized
particles can be efficient along the Kerr black hole symmetry axis
parallel to the magnetic field lines. We show that a strong acceleration
of the ionized particles to ultra-relativistic velocities is preferred
in the direction close to the magnetic field lines. Therefore, the
process of ionization of Keplerian discs around the Kerr black holes can
serve as a model of relativistic jets.
Authors:
Stuchlík, Zdeněk; Kološ, Martin;