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.
Read More
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.
Read More
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'.
Read More
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.
Read More
Relevant properties of test-particle equatorial circular orbits in the Kerr-anti-de Sitter spacetimes, including their existence, stability and orientation, are briefly discussed.
Read More
The appearance of corotating Keplerian discs orbiting Kerr superspinars
has been shown to be strongly dependent on the value of the superspinar
spin in both their shape and frequency shift profile, demonstrating
clear distinctions from the corotating discs around black holes.
However, it has to be modified in the innermost parts of the disc by the
self-illumination effect caused by the photons trapped in the strong
gravitational field near the superspinars with spin a < 9. Here we
demonstrate that self-illumination is irrelevant for counter-rotating
Keplerian discs orbiting in the field of all Kerr superspinars since
such discs are located at the regions where none of the radiated photons
can be trapped. Therefore, the results obtained by considering the
escaping photons only are quite relevant for the appearance of the
counter-rotating Keplerian discs orbiting Kerr superspinars. The
appearance and spectral continuum of such discs differ from those of
counter-rotating discs in the field of Kerr black holes. The differences
are of quantitative character except the existence of the disc images
located inside the image of the inner edge of the disc that are created
by photons reaching regions close to the surface of Kerr superspinars.
Their observational relevance is realistic in the near future for
accretion phenomena in the vicinity of Sgr A*.
Read More
Extremely Compact Stars (ECS) contain trapped null geodesics. When such objects enter the evolution period admitting geodetical motion of neutrinos, certain part of neutrinos produced in their interior will be trapped influencing their neutrino luminosity and thermal evolution. We study neutrino trapping in the braneworld ECS, assuming uniform distribution of neutrino emissivity and massless neutrinos. We give the efficiency of the neutrino trapping effects in the framework of the simple model of the internal spacetime with uniform distribution of energy density, and external spacetime described by the Reissner-Nordström geometry characterized by the braneworld "tidal" parameter b. For b < 0 the external spacetime is of the black-hole type, while for b > 0 the external spacetime can be of both black-hole and naked-singularity type. Then the ECS surface radius R can be located also above the unstable (outer) photon circular orbit. Such basically new types of the spacetimes strongly alter the trapping phenomena as compared to the standard case of b = 0. It is shown that the neutrino trapping effects are slightly lowered by the presence of physically more plausible case of b < 0, as compared to the standard internal Schwarzschild spacetime, while they can be magnified by positive tidal charges if b < 1 and lowered for b > 1. However, potential astrophysical relevance of the trapping phenomena is strongly enhanced for negative tidal charges enabling a significant enlargement of the ECS surface radius to values coherent with recent observations.
Read More
Extremely Compact Stars (ECS) contain trapped null geodesics. When such
objects enter the evolution period admitting geodetical motion of
neutrinos, certain part of neutrinos produced in their interior will be
trapped influencing their neutrino luminosity and thermal evolution. We
study neutrino trapping in the braneworld ECS, assuming uniform
distribution of neutrino emissivity and massless neutrinos. We give the
efficiency of the neutrino trapping effects in the framework of the
simple model of the internal spacetime with uniform distribution of
energy density, and external spacetime described by the
Reissner-Nordström geometry characterized by the braneworld "tidal"
parameter b. For b < 0 the external spacetime is of the black-hole
type, while for b > 0 the external spacetime can be of both
black-hole and naked-singularity type. Then the ECS surface radius R can
be located also above the unstable (outer) photon circular orbit. Such
basically new types of the spacetimes strongly alter the trapping
phenomena as compared to the standard case of b = 0. It is shown that
the neutrino trapping effects are slightly lowered by the presence of
physically more plausible case of b < 0, as compared to the standard
internal Schwarzschild spacetime, while they can be magnified by
positive tidal charges if b < 1 and lowered for b > 1. However,
potential astrophysical relevance of the trapping phenomena is strongly
enhanced for negative tidal charges enabling a significant enlargement
of the ECS surface radius to values coherent with recent observations.
Read More
We used the equations of state (EoS) of dense nuclear matter to construct the macroscopic properties of neutron stars and test them using available observational results. The Dirac-Brueckner-Hartree-Fock mean field calculations approximated by their parameterized form are the basis of our calculations for the star interior. We calculated the central pressure, density, radius and mass both without and with allowance for hyperons, and compared these results with astronomical observations.
Read More
Astrophysical fluids may acquire nonzero electrical charge because of strong irradiation or charge separation in a magnetic field. In this case, electromagnetic and gravitational forces may act together and produce new equilibrium configurations, which are different from the uncharged ones. Following our previous studies of charged test particles and uncharged perfect fluid tori encircling compact objects, we introduce here a simple test model of a charged perfect fluid torus in strong gravitational and electromagnetic fields. In contrast to ideal magnetohydrodynamic models, we consider here the opposite limit of negligible conductivity, where the charges are tied completely to the moving matter. This is an extreme limiting case which can provide a useful reference against which to compare subsequent more complicated astrophysically motivated calculations. To clearly demonstrate the features of our model, we construct three-dimensional axisymmetric charged toroidal configurations around Reissner-Nordström black holes and compare them with equivalent configurations of electrically neutral tori.
Read More
