Publication date: May 2008
Abstract:
Near a black hole or an ultracompact star, the motion of particles is
governed by a strong gravitational field. Electrically charged particles
also feel the electromagnetic force arising due to currents inside the
star or plasma circling around. We study the possibility that the
interplay between gravitational and electromagnetic actions may allow
for the stable, energetically bound off-equatorial motion of charged
particles. This would represent the well-known generalized
Störmer’s ‚halo orbits‘, which have been discussed in connection
with the motion of dust grains in planetary magnetospheres. We
demonstrate that such orbits exist and can be astrophysically relevant
when a compact star or a black hole is endowed with a dipole-type
magnetic field. In the case of the Kerr Newman solution, numerical
analysis shows that the mutually connected gravitational and
electromagnetic fields do not allow the existence of stable halo orbits
above the outer horizon of black holes. Such orbits are either hidden
under the inner black-hole horizon, or they require the presence of a
naked singularity.
Authors:
Kovář, Jiří; Stuchlík, Zdeněk; Karas, Vladimír;