We study the motion of current carrying charged string loops in the
Reissner-Nordström black hole background combining the gravitational and
electromagnetic field. Introducing new electromagnetic interaction
between central charge and charged string loop makes the string loop
equations of motion to be non-integrable even in the flat spacetime
limit, but it can be governed by an effective potential even in the
black hole background. We classify different types of the string loop
trajectories using effective potential approach, and we compare the
innermost stable string loop positions with loci of the charged particle
innermost stable orbits. We examine string loop small oscillations
around minima of the string loop effective potential, and we plot radial
profiles of the string loop oscillation frequencies for both the radial
and vertical modes. We construct charged string loop quasi-periodic
oscillations model and we compare it with observed data from
microquasars GRO 1655-40, XTE 1550-564, and GRS 1915+105. We also study
the acceleration of current carrying string loops along the vertical
axis and the string loop ejection from RN black hole neighbourhood,
taking also into account the electromagnetic interaction.
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We construct the light escape cones of isotropic spot sources of
radiation residing in special classes of reference frames in the Kerr-de
Sitter (KdS) black hole spacetimes, namely in the fundamental class of
`non-geodesic' locally non-rotating reference frames (LNRFs), and two
classes of `geodesic' frames, the radial geodesic frames (RGFs), both
falling and escaping, and the frames related to the circular geodesic
orbits (CGFs). We compare the cones constructed in a given position for
the LNRFs, RGFs, and CGFs. We have shown that the photons locally
counter-rotating relative to LNRFs with positive impact parameter and
negative covariant energy are confined to the ergosphere region.
Finally, we demonstrate that the light escaping cones govern the shadows
of black holes located in front of a radiating screen, as seen by the
observers in the considered frames. For shadows related to distant
static observers the LNRFs are relevant.
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We investigate particle motion and collisions in the vicinity of
rotating black holes immersed in combined cosmological quintessential
scalar field and external magnetic field. The quintessential dark-energy
field governing the spacetime structure is characterized by the
quintessential state parameter ωq ∈ (-1; -1/3) characterizing its
equation of state, and the quintessential field-intensity parameter c
determining the static radius where the black hole attraction is just
balanced by the quintessential repulsion. The magnetic field is assumed
to be test field that is uniform close to the static radius, where the
spacetime is nearly flat, being characterized by strength B there.
Deformations of the test magnetic field in vicinity of the black hole,
caused by the Ricci non-flat spacetime structure are determined. General
expression of the center-of-mass energy of the colliding charged or
uncharged particles near the black hole is given and discussed in
several special cases. In the case of nonrotating black holes, we
discuss collisions of two particles freely falling from vicinity of the
static radius, or one such a particle colliding with charged particle
revolving at the innermost stable circular orbit. In the case of
rotating black holes, we discuss briefly particles falling in the
equatorial plane and colliding in close vicinity of the black hole
horizon, concentrating attention to the interplay of the effects of the
quintessential field and the external magnetic field. We demonstrate
that the ultra-high center-of-mass energy can be obtained for black
holes placed in an external magnetic field for an infinitesimally small
quintessential field-intensity parameter c; the center-of-mass energy
decreases if the quintessential field-intensity parameter c increases.
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We study the dynamics of charged test particles in the vicinity of a
black hole immersed into an asymptotically uniform external magnetic
field. A real magnetic field around a black hole will be far away from
to be completely regular and uniform, a uniform magnetic field is used
as linear approximation. Ionized particle acceleration, charged particle
oscillations and synchrotron radiation of moving charged particle have
been studied.
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The possibility that two toroidal accretion configurations may be
orbiting around a~super--massive Kerr black hole has been addressed.
Such tori may be formed during different stages of the Kerr attractor
accretion history. We consider the relative rotation of the tori and the
corotation or counterrotation of a~single torus with respect to the Kerr
attractor. We give classification of the couples of accreting and non--
accreting tori in dependence on the Kerr black hole dimensionless spin.
We demonstrate that only in few cases a~double accretion tori system may
be formed under specific conditions.
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We study the general motion of photons in the Kerr-de Sitter black-hole
and naked singularity spacetimes. The motion is governed by the impact
parameters X, related to the axial symmetry of the spacetime, and q,
related to its hidden symmetry. Appropriate `effective potentials'
governing the latitudinal and radial motion are introduced and their
behavior is examined by the `Chinese boxes' technique giving regions
allowed for the motion in terms of the impact parameters. Restrictions
on the impact parameters X and q are established in dependence on the
spacetime parameters M, Λ , a. The motion can be of orbital type
(crossing the equatorial plane, q>0) and vortical type (tied above or
below the equatorial plane, q<0). It is shown that for negative
values of q, the reality conditions imposed on the latitudinal motion
yield stronger constraints on the parameter X than that following from
the reality condition of the radial motion, excluding the existence of
vortical motion of constant radius. The properties of the spherical
photon orbits of the orbital type are determined and used along with the
properties of the effective potentials as criteria of classification of
the KdS spacetimes according to the properties of the motion of the
photon.
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The study of quasi-periodic oscillations (QPOs) of X-ray flux observed
in the stellar-mass black hole binaries can provide a powerful tool for
testing of the phenomena occurring in the strong gravity regime.
Magnetized versions of the standard geodesic models of QPOs can explain
the observationally fixed data from the three microquasars. We perform a
successful fitting of the HF QPOs observed for three microquasars, GRS
1915+105, XTE 1550-564 and GRO 1655-40, containing black holes, for
magnetized versions of both epicyclic resonance and relativistic
precession models and discuss the corresponding constraints of
parameters of the model, which are the mass and spin of the black hole
and the parameter related to the external magnetic field. The estimated
magnetic field intensity strongly depends on the type of objects giving
the observed HF QPOs. It can be as small as 10^{-5} G if electron
oscillatory motion is relevant, but it can be by many orders higher for
protons or ions (0.02-1 G), or even higher for charged dust or such
exotic objects as lighting balls, etc. On the other hand, if we know by
any means the magnetic field intensity, our model implies strong limit
on the character of the oscillating matter, namely its specific charge.
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In this work we present investigation of the escape cones of null-
geodesics from the interior of rotating homogeneous compact stars in the
model, where only terms linear in the star's rotational frequency are
assumed. We focus on the single model of the star with particular radius
R = 2.8M (using units in which c = G = 1) rotating with different values
of angular momentum J. We vary the position of the isotropically
radiating source both in radial and latitudinal direction and we show
the impact of the position and the rotational rate on the shape of the
escape cone of null-geodesics. We find that even for small rotational
rate corresponding to j = J/M2 = 0.1 the impact on the escape cones is
rather strong. The escape cones are no longer symmetrical around radial
direction, and it is clearly seen that the radiation in the direction of
the rotation can easily reach the infinity. On the other hand, the
radiation in the direction opposite to the rotation will be trapped in
the interior of the star. We discuss possible astrophysical relevance of
our results.
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We demonstrate that the generic charged rotating regular black hole
solutions of general relativity coupled to non-linear electrodynamics,
obtained by using the alternate Newman-Janis algorithm, introduces only
small (on level 10-2) inconsistency in the behaviour of the
electrodynamics Lagrangian. This approves application of these analytic
and simple solutions as astrophysically relevant, sufficiently precise
approximate solutions describing rotating regular black holes.
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The possibility that two toroidal accretion configurations may be
orbiting around a super-massive Kerr black hole has been addressed. Such
tori may be formed during different stages of the Kerr attractor
accretion history. We consider the relative rotation of the tori and the
corotation or counterrotation of a single torus with respect to the Kerr
attractor. We give classification of the couples of accreting and non-
accreting tori in dependence on the Kerr black hole dimensionless spin.
We demonstrate that only in few cases a double accretion tori system may
be formed under specific conditions.
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