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.
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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.
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We study the non-monotonic Keplerian velocity profiles related to locally non-rotating frames (LNRF) in the field of near-extreme braneworld Kerr black holes and naked singularities in which the non-local gravitational effects of the bulk are represented by a braneworld tidal charge b and the 4D geometry of the spacetime structure is governed by the Kerr-Newman geometry. We show that positive tidal charge has a tendency to restrict the values of the black hole dimensionless spin a admitting the existence of the non-monotonic Keplerian LNRF-velocity profiles; the non-monotonic profiles exist in the black hole spacetimes with tidal charge smaller than b = 0.410 05 (and spin larger than a = 0.768 08). With decreasing value of the tidal charge (which need not be only positive), both the region of spin allowing the non-monotonicity in the LNRF-velocity profile around braneworld Kerr black hole and the velocity difference in the minimum-maximum parts of the velocity profile increase implying growing astrophysical relevance of this phenomenon.
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We test possible observational consequences of presence of Kerr superspinars indicated by string theories. We demonstrate that such superspinars could survive up to the era of high redshift quasars. We demonstrate unusual properties of disc oscillations of Kerr superspinars and variety of unusual optical phenomena related to accretion discs orbiting them.
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Results of our recent studies suggest a possibility of existence of halo (off-equatorial) clouds consisting of non-interacting charged test particles encircling compact objects (black holes, neutron stars) surrounded by magnetic fields. Here we upgrade the basic model of such diluted toroidal structures by adding internal properties of the matter like density and pressure, so that we have more feasible description for the real charged matter. We realize it by using the magnetohydrodynamic approach. Namely, we built a model of dielectric (zero conductivity) charged torus moving in strong gravitational and electromagnetic fields in the vicinity of black holes. This approach represents just the opposite one to that of widely used ideal magnetohydrodynamics, where the infinite conductivity is taken into account. However, the zero (or negligible) conductivity seems to be one of the assumptions for the existence of charged tori circling in strong gravitational and electromagnetic fields of compact objects.
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Using the pseudo-Newtonian (PN) potential reflecting properties of the Schwarz-schild-de Sitter spacetime, we estimate the influence of the repulsive cosmological constant Λ ~ 1.3 × 10-56cm-2 implied by recent cosmological tests onto the motion of both Small and Large Magellanic Clouds (SMC and LMC) in the gravitational field of the Milky Way. Considering detailed modelling of the gravitational field of the Galaxy disc, bulge and cold dark matter halo, the trajectories of SMC and LMC constructed for the PN potential with the cosmological constant are confronted to those given for Λ = 0. In the realistic model of the extended cold dark matter halo its edge and related total mass are taken at typical values reflecting recent diversity in the total Galaxy mass estimates. In all cases, strong influence of the cosmological constant, on 10% level or higher, has been found for motion of both SMC and LMC. Inside the halo, the Newtonian part of the PN potential is exact enough, while outside the halo the PN potential can give relevant relativistic corrections. The role of the cosmological constant is most conspicuous when binding mass is estimated for the satellite galaxies. We have found a strong influence of cosmic repulsion on the total binding mass for both galaxies. For SMC there is the binding mass MSMCΛ = 0 = 7.07 × 1011M⨀ and MSMCΛ > 0 = 8.61 × 1011M⨀, while even much higher increase is found for LMC, where MLMCΛ = 0 = 1.50 × 1012M⨀ and MLMCΛ > 0 = 2.21 × 1012M⨀, putting serious doubts on the possibility that the LMC is bounded by the Milky Way. However, the estimates of binding masses are strongly influenced by initial velocity of SMC and LMC; we took the values inferred for the IAU MW rotation velocity ~ 220 km/s. Our results indicate very important role of the cosmic repulsion in the motion of interacting galaxies, clearly demonstrated in the case of the satellite SMC and LMC galaxies moving in the field of Milky Way. In some cases, the effect of the cosmic repulsion can be even comparable to the effects of the dynamical friction and the Andromeda Galaxy.
Read More
We study the non-monotonic Keplerian velocity profiles related to
locally non-rotating frames (LNRF) in the field of near-extreme
braneworld Kerr black holes and naked singularities in which the
non-local gravitational effects of the bulk are represented by a
braneworld tidal charge b and the 4D geometry of the spacetime structure
is governed by the Kerr-Newman geometry. We show that positive tidal
charge has a tendency to restrict the values of the black hole
dimensionless spin a admitting the existence of the non-monotonic
Keplerian LNRF-velocity profiles; the non-monotonic profiles exist in
the black hole spacetimes with tidal charge smaller than b = 0.410 05
(and spin larger than a = 0.768 08). With decreasing value of the tidal
charge (which need not be only positive), both the region of spin
allowing the non-monotonicity in the LNRF-velocity profile around
braneworld Kerr black hole and the velocity difference in the
minimum-maximum parts of the velocity profile increase implying growing
astrophysical relevance of this phenomenon.
Read More
We test possible observational consequences of presence of Kerr
superspinars indicated by string theories. We demonstrate that such
superspinars could survive up to the era of high redshift quasars. We
demonstrate unusual properties of disc oscillations of Kerr superspinars
and variety of unusual optical phenomena related to accretion discs
orbiting them.
Read More
Results of our recent studies suggest a possibility of existence of halo
(off-equatorial) clouds consisting of non-interacting charged test
particles encircling compact objects (black holes, neutron stars)
surrounded by magnetic fields. Here we upgrade the basic model of such
diluted toroidal structures by adding internal properties of the matter
like density and pressure, so that we have more feasible description for
the real charged matter. We realize it by using the magnetohydrodynamic
approach. Namely, we built a model of dielectric (zero conductivity)
charged torus moving in strong gravitational and electromagnetic fields
in the vicinity of black holes. This approach represents just the
opposite one to that of widely used ideal magnetohydrodynamics, where
the infinite conductivity is taken into account. However, the zero (or
negligible) conductivity seems to be one of the assumptions for the
existence of charged tori circling in strong gravitational and
electromagnetic fields of compact objects.
Read More
Using the pseudo-Newtonian (PN) potential reflecting properties of the
Schwarz-schild-de Sitter spacetime, we estimate the influence of the
repulsive cosmological constant Λ ~ 1.3 ×
10-56cm-2 implied by recent cosmological tests
onto the motion of both Small and Large Magellanic Clouds (SMC and LMC)
in the gravitational field of the Milky Way. Considering detailed
modelling of the gravitational field of the Galaxy disc, bulge and cold
dark matter halo, the trajectories of SMC and LMC constructed for the PN
potential with the cosmological constant are confronted to those given
for Λ = 0. In the realistic model of the extended cold dark
matter halo its edge and related total mass are taken at typical values
reflecting recent diversity in the total Galaxy mass estimates. In all
cases, strong influence of the cosmological constant, on 10% level or
higher, has been found for motion of both SMC and LMC. Inside the halo,
the Newtonian part of the PN potential is exact enough, while outside
the halo the PN potential can give relevant relativistic corrections.
The role of the cosmological constant is most conspicuous when binding
mass is estimated for the satellite galaxies. We have found a strong
influence of cosmic repulsion on the total binding mass for both
galaxies. For SMC there is the binding mass MSMCΛ
= 0 = 7.07 × 1011M⨀ and
MSMCΛ > 0 = 8.61 ×
1011M⨀, while even much higher increase is
found for LMC, where MLMCΛ = 0 = 1.50
× 1012M⨀ and
MLMCΛ > 0 = 2.21 ×
1012M⨀, putting serious doubts on the
possibility that the LMC is bounded by the Milky Way. However, the
estimates of binding masses are strongly influenced by initial velocity
of SMC and LMC; we took the values inferred for the IAU MW rotation
velocity ~ 220 km/s. Our results indicate very important role of the
cosmic repulsion in the motion of interacting galaxies, clearly
demonstrated in the case of the satellite SMC and LMC galaxies moving in
the field of Milky Way. In some cases, the effect of the cosmic
repulsion can be even comparable to the effects of the dynamical
friction and the Andromeda Galaxy.
Read More
