In the framework of the braneworld models, rotating black holes can be
described by the Kerr metric with a tidal charge representing the
influence of the non-local gravitational (tidal) effects of the bulk
space Weyl tensor onto the black hole spacetime. We study the influence
of the tidal charge onto profiled spectral lines generated by radiating
tori orbiting in vicinity of a rotating black hole. We show that with
lowering the negative tidal charge of the black hole, the profiled line
becomes to be flatter and wider keeping their standard character with
flux stronger at the blue edge of the profiled line. The extension of
the line grows with radius falling and inclination angle growing. With
growing inclination angle a small hump appears in the profiled lines due
to the strong lensing effect of photons coming from regions behind the
black hole. For positive tidal charge ( b > 0) and high inclination
angles two small humps appear in the profiled lines close to the red and
blue edge of the lines due to the strong lensing effect. We can conclude
that for all values of b, the strongest effect on the profiled lines
shape (extension) is caused by the changes of the inclination angle.
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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. The orbital Keplerian frequency v K and the radial and vertical epicyclic frequencies v r, v θ of the equatorial, quasicircular geodetical motion are given. Their radial profiles related to Keplerian accretion discs are discussed, assuming the inner edge of the disc located at the innermost stable circular geodesic. For completeness, naked singularity spacetimes are considered too. The resonant conditions are given in three astrophysically relevant situations: for direct (parametric) resonances of the oscillations with the radial and vertical epicyclic frequencies, for the relativistic precession model, and for some trapped oscillations of the warped discs, with resonant combinational frequencies involving the Keplerian and radial epicyclic frequencies. It is shown, how the tidal charge could influence matching of the observational data indicating the 3 : 2 frequency ratio observed in GRS 1915 + 105 microquasar with prediction of the orbital resonance model; limits on allowed range of the black hole parameters a and b are established. The “magic” dimensionless black hole spin enabling presence of strong resonant phenomena at the radius, where v K: v θ : v r = 3 : 2 : 1, is determined in dependence on the tidal charge. Such strong resonances could be relevant even in sources with highly scattered resonant frequencies, as those expected in Sgr A*. The specific values of the spin and tidal charge are given also for existence of specific radius where v K : v θ : v r = s : t : u with 5≥ s > t > u being small natural numbers. It is shown that for some ratios such situation is impossible in the field of black holes. We can conclude that analysing the microquasars high-frequency QPOs in the framework of orbital resonance models, we can put relevant limits on the tidal charge of brany Kerr black holes.
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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. The orbital Keplerian
frequency v K and the radial and vertical epicyclic
frequencies v r, v θ of the equatorial,
quasicircular geodetical motion are given. Their radial profiles related
to Keplerian accretion discs are discussed, assuming the inner edge of
the disc located at the innermost stable circular geodesic. For
completeness, naked singularity spacetimes are considered too. The
resonant conditions are given in three astrophysically relevant
situations: for direct (parametric) resonances of the oscillations with
the radial and vertical epicyclic frequencies, for the relativistic
precession model, and for some trapped oscillations of the warped discs,
with resonant combinational frequencies involving the Keplerian and
radial epicyclic frequencies. It is shown, how the tidal charge could
influence matching of the observational data indicating the 3 : 2
frequency ratio observed in GRS 1915 + 105 microquasar with prediction
of the orbital resonance model; limits on allowed range of the black
hole parameters a and b are established. The “magic”
dimensionless black hole spin enabling presence of strong resonant
phenomena at the radius, where v K: v θ :
v r = 3 : 2 : 1, is determined in dependence on the tidal
charge. Such strong resonances could be relevant even in sources with
highly scattered resonant frequencies, as those expected in Sgr A*. The
specific values of the spin and tidal charge are given also for
existence of specific radius where v K : v θ
: v r = s : t : u with 5≥ s > t > u being
small natural numbers. It is shown that for some ratios such situation
is impossible in the field of black holes. We can conclude that
analysing the microquasars high-frequency QPOs in the framework of
orbital resonance models, we can put relevant limits on the tidal charge
of brany Kerr black holes.
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We present results of investigation of the off-equatorial circular orbits existence in the vicinity of neutron stars, Schwarzschild black holes with plasma ring, and near Kerr-Newman black holes and naked singularities.
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We present results of investigation of the off-equatorial circular
orbits existence in the vicinity of neutron stars, Schwarzschild black
holes with plasma ring, and near Kerr-Newman black holes and naked
singularities.
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Extremely compact objects (9GM/4c2 < R < 3GM/c2) contain trapped null geodesics. When such objects enter the evolution period corresponding to the geodetical motion of neutrinos, a certain part of neutrinos produced in their interior will be trapped influencing thus neutrino luminosity of the objects and consequently their thermal evolution. The existence of trapped neutrinos indicates possibility of 'two-temperature' cooling regime of the extremely compact objects. We present upper estimates on the efficiency of the neutrino trapping effects obtained in the framework of the simplest model of the internal Schwarzschild spacetime with uniform distribution of energy density, assuming uniform distribution of neutrino emissivity. We introduce a 'global' luminosity trapping coefficient representing influence of the trapping effect on the total neutrino luminosity of the extremely compact objects and cooling trapping coefficients of both 'local' and 'global' kinds characterizing influence of the trapping on the cooling process. It is shown that the trapping of neutrinos can be relevant to moderately or even slightly extremely compact objects.
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Extremely compact objects (9GM/4c2 < R <
3GM/c2) contain trapped null geodesics. When such objects
enter the evolution period corresponding to the geodetical motion of
neutrinos, a certain part of neutrinos produced in their interior will
be trapped influencing thus neutrino luminosity of the objects and
consequently their thermal evolution. The existence of trapped neutrinos
indicates possibility of 'two-temperature' cooling regime of the
extremely compact objects. We present upper estimates on the efficiency
of the neutrino trapping effects obtained in the framework of the
simplest model of the internal Schwarzschild spacetime with uniform
distribution of energy density, assuming uniform distribution of
neutrino emissivity. We introduce a 'global' luminosity trapping
coefficient representing influence of the trapping effect on the total
neutrino luminosity of the extremely compact objects and cooling
trapping coefficients of both 'local' and 'global' kinds characterizing
influence of the trapping on the cooling process. It is shown that the
trapping of neutrinos can be relevant to moderately or even slightly
extremely compact objects.
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We present results of our recent studies concerning effects of Λ > 0 in astrophysically motivated problems. Here we summarize properties of circular geodesic motion of test particles in the equatorial plane of Kerr-de Sitter black-hole and naked-singularity spacetimes. Along with the standard analysis of geodesic equations of the ordinary geometry, we introduce alternative inertial forces formalism defined within the General Theory of Relativity in the framework of optical reference geometry.
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Results of our recent studies concerning possible effects of Λ > 0 for equilibrium positions of spinning test particles and stationary configurations of perfect-fluid tori are presented.
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We study the influence of the tidal charge parameter of the braneworld models on some optical phenomena in rotating black hole space-times. The escape photon cones are determined for special families of locally nonrotating, circular geodetical and radially free-falling observers. The silhouette of a rotating black hole, the shape of an equatorial thin accretion disk and the time delay effect for direct and indirect images of a radiating hot spot orbiting the black hole are given and classified in terms of the black hole rotational and tidal parameters. It is shown that increase of the negatively valued tidal parameter, with the rotational parameter fixed, generally strengthens the relativistic effects and suppresses the rotation-induced asymmetries in the optical phenomena.
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