The possibility that two toroidal accretion configurations may be orbiting around a~super--massive Kerr black hole has been addressed. Such tori may be formed during different stages of the Kerr attractor accretion history. We consider the relative rotation of the tori and the corotation or counterrotation of a~single torus with respect to the Kerr attractor. We give classification of the couples of accreting and non--accreting tori in dependence on the Kerr black hole dimensionless spin. We demonstrate that only in few cases a~double accretion tori system may be formed under specific conditions.
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We present our study of bending of null geodesics in the regular spacetimes, particularly in Bardeen and Ayon-Beato-Garcia (ABG) no-horizon spacetimes. We show that thanks to "flatness" of these spacetimes in the central region there exist interesting optical phenomena related to photons with small impact parameters traveling through such gravitational field. There exist a critical impact parameter which gives maximal deflection of light in the Bardeen and ABG no-horizon spacetimes. We discuss "ghost" direct and indirect images of Keplerian discs which are generated by photons with small impact parameters and to the classical scattering cross section in such regular but strongly curved spacetimes.
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In the case of no-horizon regular spacetimes there exist a region close to origin where the spacetime is "flattened". Existence of such a region leads to presence of so called "ghost" images of accretion discs orbiting in the spacetimes. We show how the presence of the ghost images influences distribution of photons in the profiles of spectral lines generated by Keplerian disks.
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We study the general motion of photons in the Kerr-de Sitter black-hole and naked singularity spacetimes. The motion is governed by the impact parameters X, related to the axial symmetry of the spacetime, and q, related to its hidden symmetry. Appropriate `effective potentials' governing the latitudinal and radial motion are introduced and their behavior is examined by the `Chinese boxes' technique giving regions allowed for the motion in terms of the impact parameters. Restrictions on the impact parameters X and q are established in dependence on the spacetime parameters M, Λ , a. The motion can be of orbital type (crossing the equatorial plane, q>0) and vortical type (tied above or below the equatorial plane, q<0). It is shown that for negative values of q, the reality conditions imposed on the latitudinal motion yield stronger constraints on the parameter X than that following from the reality condition of the radial motion, excluding the existence of vortical motion of constant radius. The properties of the spherical photon orbits of the orbital type are determined and used along with the properties of the effective potentials as criteria of classification of the KdS spacetimes according to the properties of the motion of the photon.
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The study of quasi-periodic oscillations (QPOs) of X-ray flux observed in the stellar-mass black hole binaries can provide a powerful tool for testing of the phenomena occurring in the strong gravity regime. Magnetized versions of the standard geodesic models of QPOs can explain the observationally fixed data from the three microquasars. We perform a successful fitting of the HF QPOs observed for three microquasars, GRS 1915+105, XTE 1550-564 and GRO 1655-40, containing black holes, for magnetized versions of both epicyclic resonance and relativistic precession models and discuss the corresponding constraints of parameters of the model, which are the mass and spin of the black hole and the parameter related to the external magnetic field. The estimated magnetic field intensity strongly depends on the type of objects giving the observed HF QPOs. It can be as small as 10^{-5} G if electron oscillatory motion is relevant, but it can be by many orders higher for protons or ions (0.02-1 G), or even higher for charged dust or such exotic objects as lighting balls, etc. On the other hand, if we know by any means the magnetic field intensity, our model implies strong limit on the character of the oscillating matter, namely its specific charge.
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In this work we present investigation of the escape cones of null-geodesics from the interior of rotating homogeneous compact stars in the model, where only terms linear in the star's rotational frequency are assumed. We focus on the single model of the star with particular radius R = 2.8M (using units in which c = G = 1) rotating with different values of angular momentum J. We vary the position of the isotropically radiating source both in radial and latitudinal direction and we show the impact of the position and the rotational rate on the shape of the escape cone of null-geodesics. We find that even for small rotational rate corresponding to j = J/M2 = 0.1 the impact on the escape cones is rather strong. The escape cones are no longer symmetrical around radial direction, and it is clearly seen that the radiation in the direction of the rotation can easily reach the infinity. On the other hand, the radiation in the direction opposite to the rotation will be trapped in the interior of the star. We discuss possible astrophysical relevance of our results.
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We demonstrate that the generic charged rotating regular black hole solutions of general relativity coupled to non-linear electrodynamics, obtained by using the alternate Newman-Janis algorithm, introduces only small (on level 10-2) inconsistency in the behaviour of the electrodynamics Lagrangian. This approves application of these analytic and simple solutions as astrophysically relevant, sufficiently precise approximate solutions describing rotating regular black holes.
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The possibility that two toroidal accretion configurations may be orbiting around a super-massive Kerr black hole has been addressed. Such tori may be formed during different stages of the Kerr attractor accretion history. We consider the relative rotation of the tori and the corotation or counterrotation of a single torus with respect to the Kerr attractor. We give classification of the couples of accreting and non-accreting tori in dependence on the Kerr black hole dimensionless spin. We demonstrate that only in few cases a double accretion tori system may be formed under specific conditions.
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We introduce a general transformation leading to an integral form of pressure equations characterizing equilibrium configurations of charged perfect fluid circling in strong gravitational and combined electromagnetic fields. The transformation generalizes our recent analytical treatment applicable to electric or magnetic fields treated separately along with the gravitational one. As an example, we present a particular solution for a fluid circling close to a charged rotating black hole immersed in an asymptotically uniform magnetic field.
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In this work we investigate the motion of free particle in the field of strongly gravitating object which is embedded into dust cosmological background. We use newly obtained exact solution of Einstein equations in comoving coordinates for the system under consideration in case of zero spatial curvature. Observable velocity of the particle moving relatively to the observer comoving with cosmological expansion is found from geodesic equations.
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