We present results of the study of some astrophysical phenomena taking place in the vicinity of superspinars, described by the Kerr naked singularity spacetime, that are capable to explain optical and other effects usually attributed to rotating black holes.
Read More
Binary pulsars represent a good laboratory for testing field theories in strong field regime. In such cases, the effects of non-linear terms in these theories would be easily measured. In the present work, we discuss an exact solution of Einstein's field equations, in a field representing a binary compact object. The solution is a time-dependent one, which reduces to Curzon field, in the static case. The equations of motion of a test particle in the above mentioned field are formulated and solved. These equations can be used to study the motion of a third body (or a photon) in the field of a binary system.
Read More
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.
Read More
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.
Read More
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.
Read More
Pseudo-Newtonian gravitational potential introduced in spherically
symmetric black-hole spacetimes with a repulsive cosmological constant
is tested for equilibrium toroidal configurations of barotropic perfect
fluid orbiting the black holes. Shapes and potential depths are
determined for the marginally stable barotropic tori with uniform
distribution of specific angular momentum, using both the
pseudo-Newtonian and fully relativistic approach. For the adiabatic
(isoentropic) perfect fluid, temperature profiles, mass-density and
pressure profiles and total masses of pseudo-Newtonian and relativistic
tori are compared providing important information on the relevance of
the test-disc approximation in both the approaches. It is shown that the
pseudo-Newtonian approach can be precise enough and useful for the
modelling of accretion discs in the Schwarzschild-de Sitter spacetimes
with the cosmological parameter y = ΛM2/3 lsim
10-6. For astrophysically relevant black holes with y <
10-25, this statement is tested and shown to be precise in
few per cent for both accretion and excretion tori and for the
marginally bound, i.e. maximally extended, tori allowing simultaneous
inflow to the black hole and outflow to the outer space.
Read More
Pseudo-Newtonian gravitational potential introduced in spherically symmetric black-hole spacetimes with a repulsive cosmological constant is tested for equilibrium toroidal configurations of barotropic perfect fluid orbiting the black holes. Shapes and potential depths are determined for the marginally stable barotropic tori with uniform distribution of specific angular momentum, using both the pseudo-Newtonian and fully relativistic approach. For the adiabatic (isoentropic) perfect fluid, temperature profiles, mass-density and pressure profiles and total masses of pseudo-Newtonian and relativistic tori are compared providing important information on the relevance of the test-disc approximation in both the approaches. It is shown that the pseudo-Newtonian approach can be precise enough and useful for the modelling of accretion discs in the Schwarzschild-de Sitter spacetimes with the cosmological parameter y = ΛM2/3 lsim 10-6. For astrophysically relevant black holes with y < 10-25, this statement is tested and shown to be precise in few per cent for both accretion and excretion tori and for the marginally bound, i.e. maximally extended, tori allowing simultaneous inflow to the black hole and outflow to the outer space.
Read More
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.
Read More
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.
Read More
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.
Read More
