Humpy profile of the LNRF-related orbital velocity was found for
accretion discs orbiting rapidly rotating Kerr black holes with a spin a
> 0.9953 (Keplerian discs) and a > 0.99979 (marginally stable
thick discs). Maximal positive rate of change of the orbital velocity in
terms of the proper radial distance is used to define a local frequency
characterising possible physical processes in the disc connected with
the velocity hump. Comparing the "humpy frequency" related to distant
observers with epicyclic frequencies of perturbed orbital motion, it was
shown that in Keplerian discs orbiting near-extreme Kerr black holes (a
> 0.998) the the ratio of radial epicyclic frequency and humpy
frequency (both evaluated at the same radius) is in terms of small
integers asymptotically going to the ratio 3:2 for a → 1. The
Extended Orbital Resonance Model with non-linear hump-induced
oscillations was applied to two X-ray variable sources GRS 1915+105 and
XTE J1650-500. In the case of GRS 1915+105, the model is able to address
the whole set of reported QPOs, giving the mass and spin of the central
black hole: a = 0.9998; M = 14:8M⊙. For XTE J1650-500,
similar ideas give values a = 0.9982; M = 5:1M⊙.
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We summarize influence of the tidal charge parameter of the braneworld
models onto some optical phenomena in rotating black hole spacetimes.
The shape of an equatorial thin accretion disk and profiled spectral
lines of thin keplerian rings around the black holes are given and
classified in terms of the black hole rotational and tidal parameters.
It is shown that rising of negatively-valued tidal parameter, with
rotational parameter fixed, generally strengthens the relativistic
effects and suppresses the rotation induced asymmetries in the optical
phenomena.
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Relevant properties of test-particle equatorial circular orbits in the
Kerr-anti-de Sitter spacetimes, including their existence, stability and
orientation, are briefly discussed.
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Marginally stable perfect fluid tori with uniform distribution of
specific angular momentum are determined in the
Reissner-Nordström-(anti-)de Sitter black-hole and nakedsingularity
spacetimes. Toroidal configurations are allowed only in the spacetimes
admitting existence of stable circular geodesics. The configurations
with equipotential surfaces crossing itself in a cusp allow accretion
(inner cusp) and/or excretion (outer cusp) of matter from the toroidal
configuration.
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We study properties of the off-equatorial motion of charged particles
near compact objects endowed with magnetic fields. We pay attention to
the circular orbits as well as to the general motion in the related
off-equatorial potential `halo lobes'.
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Pseudo-Newtonian gravitational potential for spherically symmetric
black-hole space-times with a repulsive cosmological constant is applied
to equilibrium toroidal configurations of barotropic perfect fluid
orbiting black holes. The results are presented for marginally stable
barotropic tori with uniform distribution of the specific angular
momentum. For the adiabatic (isoentropic) perfect fluid, temperature
profiles, mass-density and pressure profiles are calculated.
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The influence of the observed relict vacuum energy on the fluctuations
of CMBR going through cosmological matter condensations is studied in
the framework of the Einstein-Strauss-de Sitter vakuola model. It is
shown that refraction of light at the matching surface of the vakuola
and the expanding Friedman universe can be very important during
accelerated expansion of the universe, when the velocity of the matching
surface relative to static Schwarzchildian observers becomes
relativistic. Relevance of the refraction effect for the temperature
fluctuations of CMBR is given in terms of the redshift and the angular
extension of the fluctuating region.
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Rotating black holes in the brany universe of the Randall—Sundrum
type with infinite additional dimension are described by the Kerr
geometry with a tidal charge b representing the interaction of the brany
black hole and the bulk spacetime. For b < 0 rotating black holes
with dimensionless spin a > 1 are allowed. We investigate the role of
the tidal charge in the orbital resonance model of quasiperiodic
oscillations (QPOs) in black hole systems.
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We present equation of state of dense nuclear matter based on
relativistic Brueckner—Hartree—Fock theory. The models of
static neutron stars are calculated. The results are compared with
neutron star models based on Skyrme equations of state and with models
of strange stars following MIT bag model.
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We present estimates on the efficiency of neutrino trapping in brany
extremely compact stars, using the simplest model with uniform
distribution of energy density, assuming massless neutrinos and uniform
distribution of neutrino emissivity. Computation have been done for two
different uniform-density stellar solution in the Randall-Sundrum II
type braneworld, namely with the Reissner-Nordström-type of
geometry and the second one, derived by Germani and
Maartens.1
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