The role 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 the accelerated expansion of the universe when the velocity of the matching surface relative to static Schwarzschildian observers becomes relativistic.
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We consider appearance of isotropically radiating sources located at a sphere at the static radius of the Schwarzschild-de Sitter spacetimes to static observers in vicinity of the black hole horizon and the cosmological horizon and to radially moving observers. We expect these observers to follow geodesics starting from the static radius. It is shown that the observed flux diverges at both the horizons for both classes of observers. Nevertheless the frequency shift remains finite at the horizons for the radially moving observers.
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Definition of the inertial forces in the framework of the optical reference geometry is applied to the stationary and axially symmmetric Kerr-de Sitter spacetimes. The attention is restricted to the inertial forces acting on particles moving along circular orbits in the equatorial plane of these spacetimes. It is shown, where the gravitational force vanishes, and where the centrifugal force vanishes independently of velocities of test particles. The Coriolis force does not vanish for a non-zero velocity.
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Solutions of general relativistic field equations for static, spherically symmetric, equilibrium perfect-fluid configurations obeying the polytropic and adiabatic equation of state in the presence of a repulsive cosmological constant are discussed. The influence of the cosmological constant on the total mass of the configurations, their radius and the profiles of energy density, rest energy density, pressure and metric coefficients is studied and compared for the polytropic and adiabatic case. The static equilibrium configurations are allowed for σ<σ_{crit} (α<α_{crit}), where the critical values σ_{crit} (α_{crit}) of the relativity parameter σ (α) ≡ pcent/rhocent c^{2} of the polytropes (adiabates) depend on the cosmological constant and the polytropic index n of the equation of state and can be determined by a numerical procedure. The numerical results show that for sufficiently small values of the relativity parameter σ=α≪ σ_{crit}, the polytropic spheres are more compact than the adiabatic ones. Increase of the cosmological constant causes increase of both the radius and mass of the spheres and makes the profiles of the metric coefficients flatter. For large values of the relativity paramater, σ=α≲ σ_{crit}, the situation is more complex and depends also on the value of the polytropic parameter n. The mass of the adiabatic spheres can exceed the mass of the polytropes for n≳ 2. In the case of n=3, the adiabatic spheres can even be more compact than the polytropic ones. Generally, the role of the cosmological constant is supressed with both σ=α and n growing.
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In all four microquasars which show twin peak kHz QPOs, the ratio of the two frequencies is 3:2. This rather strongly supports the suggestion by Abramowicz, M. A. and Kluzniak [W. Abramowicz, M. A. and Kluzniak, W., (2001). A precise determination of black hole spin in GRO J1655-40. Astronomy and Astrophysics, 374:L19] that twin peak kHz QPOs are due to a resonance between some modes of accretion disk oscillations. Detailed studies of this suggestion revealed that several such non-linear resonances are present in nearly Keplerian disks in strong gravity. Here, we fit to observations predictions of the resonance hypothesis for two particular types of non-linear resonances between vertical and radial epicyclic frequencies. For three microquasars with known masses, the fits give an accurate estimate of the spin.
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In this Proceedings, the talks presented during workshops RAGtime 4 (14-16 October 2002, Opava, Czech Republic) and RAGtime 5 (13-15 October 2003, Opava, Czech Republic) are collected.
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Equatorial motion of test particles in Kerr de Sitter spacetimes is
considered. Circular orbits are determined, their properties are
discussed for both black-hole and naked-singularity spacetimes, and
their relevance for thin accretion disks is established. The circular
orbits constitute two families that coalesce at the so-called static
radius. The orientation of the motion along the circular orbits is, in
accordance with case of asymptotically flat Kerr spacetimes, defined by
relating the motion to the locally nonrotating frames. The minus-family
orbits are all counterrotating, while the plus-family orbits are usually
corotating relative to these frames. However, the plus-family orbits
become counterrotating in the vicinity of the static radius in all Kerr
de Sitter spacetimes, and they become counterrotating in the vicinity of
the ring singularity in Kerr de Sitter naked-singularity spacetimes with
a low enough rotational parameter. In such spacetimes, the efficiency of
the conversion of the rest energy into heat energy in the geometrically
thin plus-family accretion disks can reach extremely high values
exceeding the efficiency of the annihilation process. The transformation
of a Kerr de Sitter naked singularity into an extreme black hole due to
accretion in the thin disks is briefly discussed for both the
plus-family and minus-family disks. It is shown that such a conversion
leads to an abrupt instability of the innermost parts of the plus-family
accretion disks that can have strong observational consequences.
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Equatorial motion of test particles in Kerr de Sitter spacetimes is considered. Circular orbits are determined, their properties are discussed for both black-hole and naked-singularity spacetimes, and their relevance for thin accretion disks is established. The circular orbits constitute two families that coalesce at the so-called static radius. The orientation of the motion along the circular orbits is, in accordance with case of asymptotically flat Kerr spacetimes, defined by relating the motion to the locally nonrotating frames. The minus-family orbits are all counterrotating, while the plus-family orbits are usually corotating relative to these frames. However, the plus-family orbits become counterrotating in the vicinity of the static radius in all Kerr de Sitter spacetimes, and they become counterrotating in the vicinity of the ring singularity in Kerr de Sitter naked-singularity spacetimes with a low enough rotational parameter. In such spacetimes, the efficiency of the conversion of the rest energy into heat energy in the geometrically thin plus-family accretion disks can reach extremely high values exceeding the efficiency of the annihilation process. The transformation of a Kerr de Sitter naked singularity into an extreme black hole due to accretion in the thin disks is briefly discussed for both the plus-family and minus-family disks. It is shown that such a conversion leads to an abrupt instability of the innermost parts of the plus-family accretion disks that can have strong observational consequences.
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Many Galactic black hole and neutron star sources in low X-ray mass
binaries show QPOs (quasi periodic oscillations) in their observed X-ray
fluxes, i.e. peaks in the Fourier variability power spectra. Pairs of
twin peaks are observed, and in black-hole systems their frequencies
(upp), (down) are in rational ratios. For example, in all four
microquasars with twin peaks observed, (upp):(down) = 3:2. The rational
ratios have been postulated in a model that explained twin peak QPOs as
a non-linear resonance between modes of accretion disk oscillations. For
those microquasars where the mass of the X-ray source is known, we
determine the black-hole spin, following from the observed QPO
frequencies within various models of resonance.
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Many Galactic black hole and neutron star sources in low X-ray mass binaries show QPOs (quasi periodic oscillations) in their observed X-ray fluxes, i.e. peaks in the Fourier variability power spectra. Pairs of twin peaks are observed, and in black-hole systems their frequencies (upp), (down) are in rational ratios. For example, in all four microquasars with twin peaks observed, (upp):(down) = 3:2. The rational ratios have been postulated in a model that explained twin peak QPOs as a non-linear resonance between modes of accretion disk oscillations. For those microquasars where the mass of the X-ray source is known, we determine the black-hole spin, following from the observed QPO frequencies within various models of resonance.
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