Publication date: Oct 2010
Abstract:
Accretion onto black holes and compact stars brings material in a zone
of strong gravitational and electromagnetic fields. We study dynamical
properties of motion of electrically charged particles forming a highly
diluted medium (a corona) in the regime of strong gravity and
large-scale (ordered) magnetic field. We start our work from a system
that allows regular motion, then we focus on the onset of chaos. To this
end, we investigate the case of a rotating black hole immersed in a
weak, asymptotically uniform magnetic field. We also consider a magnetic
star, approximated by the Schwarzschild metric and a test magnetic field
of a rotating dipole. These are two model examples of systems permitting
energetically bound, off-equatorial motion of matter confined to the
halo lobes that encircle the central body. Our approach allows us to
address the question of whether the spin parameter of the black hole
plays any major role in determining the degree of the chaoticness. To
characterize the motion, we construct the recurrence plots (RPs) and we
compare them with Poincaré surfaces of section. We describe the
RPs in terms of the recurrence quantification analysis, which allows us
to identify the transition between different dynamical regimes. We
demonstrate that this new technique is able to detect the chaos onset
very efficiently and provide its quantitative measure. The chaos
typically occurs when the conserved energy is raised to a sufficiently
high level that allows the particles to traverse the equatorial plane.
We find that the role of the black hole spin in setting the chaos is
more complicated than initially thought.
Authors:
Kopáček, O.; Karas, V.; Kovář, J.; Stuchlík, Z.;