34 research outputs found
Transition from regular to chaotic motion in black hole magnetospheres
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 relativity. For the first
time, we apply recurrence plots as a suitable technique to quantify the degree
of chaoticness near a black hole.Comment: PhD Thesis, 123 page
Near-horizon structure of escape zones of electrically charged particles around weakly magnetized rotating black hole. II. Acceleration and escape in the oblique magnetosphere
Strong gravity and magnetic fields are key ingredients that power processes
of accretion and ejection near compact objects. While the particular mechanisms
that operate here are still discussed, it seems that the presence of an ordered
magnetic field is crucial for the acceleration and collimation of relativistic
jets of electrically charged particles on superhorizon length scales. In this
context, we further study the effect of a large-scale magnetic field on the
dynamics of charged particles near a rotating black hole. We consider a
scenario in which the initially neutral particles on regular geodesic orbits in
the equatorial plane are destabilized by a charging process (e.g., by
photoionization). Some charged particles are accelerated out of the equatorial
plane, and they follow jetlike trajectories with relativistic velocities. In
our previous paper, we investigated this scenario for the case of perfect
alignment of the magnetic field with the axis of rotation; i.e., the system was
considered axisymmetric. Here we relax this assumption and investigate
nonaxisymmetric systems in which the magnetic field is arbitrarily inclined
with respect to the black hole spin. We study the system numerically in order
to locate the zones of escaping trajectories and compute the maximum (terminal)
escape velocity. It appears that breaking the axial symmetry (even by small
inclination angles) substantially increases the fraction of escaping orbits and
allows the acceleration to ultrarelativistic velocities that were excluded in
the axisymmetric setup. The presence of transient chaotic dynamics in the
launching region of the relativistic outflow is confirmed with chaotic
indicators.Comment: 14 pages, 8 figures; accepted for publication in ApJ; revised version
with typographical and language correction
OBLIQUE MAGNETIC FIELDS AND THE ROLE OF FRAME DRAGGING NEAR ROTATING BLACK HOLE
Magnetic null points can develop near the ergosphere boundary of a rotating black hole by the combined effects of strong gravitational field and the frame-dragging mechanism. The induced electric component does not vanish in the magnetic null and an efficient process of particle acceleration can occur in its immediate vicinity. Furthermore, the effect of imposed (weak) magnetic field can trigger an onset of chaos in the motion of electrically charged particles. The model set-up appears to be relevant for low-accretion-rate nuclei of some galaxies which exhibit episodic accretion events (such as the Milky Way's supermassive black hole) embedded in a large-scale magnetic field of external origin with respect to the central black hole. In this contribution we summarise recent results and we give an outlook for future work with the focus on the role of gravito-magnetic effects caused by rotation of the black hole