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ABSTRACT: We study backreaction of accreting matter onto a spherically symmetric black
hole in a perturbative way, when accretion is in a quasi-steady state. General
expressions for corrections to the metric coefficients are found in the
Eddington-Finkelstein coordinates. It is shown that near the horizon of a black
hole, independently of the form of the energy-momentum tensor, the leading
corrections to the metric are of the Vaidya form. The relation to other
solutions is discussed and particular examples are presented.
02/2012;
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ABSTRACT: Superheavy dark matter (SHDM) exchanges energy with its environment much slower than particles with masses close to the electroweak (EW) scale and has therefore different small-scale clustering properties. Using the neutralino as candidate for the SHDM, we find that free-streaming allows the formation of DM clumps of all masses down to $\sim 260 m_\chi$ in the case of bino. If small-scale clumps evolve from a non-standard, spiky spectrum of perturbations, DM clumps may form during the radiation dominated era. These clumps are not destroyed by tidal interactions and can be extremely dense. In the case of a bino, a "gravithermal catastrophe" can develop in the central part of the most dense clumps, increasing further the central density and thus the annihilation signal. In the case of a higgsino, the annihilation signal is enhanced by the Sommerfeld effect. As a result annihilations of superheavy neutralinos in dense clumps may lead to observable fluxes of annihilation products in the form of ultrahigh energy particles, for both cases, higgsinos and binos, as lightest supersymmetric particles. Comment: 9 pages, 2 eps figures; v2: changed title, to appear in PRD
02/2010;
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ABSTRACT: The formation and evolution of superdense clumps (or subhalos) is studied. Such clumps of dark matter (DM) can be produced by many mechanisms, most notably by spiky features in the spectrum of inflationary perturbations and by cosmological phase transitions. Being produced very early during the radiation dominated epoch, superdense clumps evolve as isolated objects. They do not belong to hierarchical structures for a long time after production, and therefore they are not destroyed by tidal interactions during the formation of larger structures. For DM particles with masses close to the electroweak (EW) mass scale, superdense clumps evolve towards a power-law density profile $\rho(r) \propto r^{-1.8}$ with a central core. Superdense clumps cannot be composed of standard neutralinos, since their annihilations would overproduce the diffuse gamma radiation. If the clumps are constituted of superheavy DM particles and develop a sufficiently large central density, the evolution of their central part can lead to a 'gravithermal catastrophe.' In such a case, the initial density profile turns into an isothermal profile with $\rho \propto r^{-2}$ and a new, much smaller core in the center. Superdense clumps can be bserved by gamma radiation from DM annihilations and by gravitational wave detectors, while the production of primordial black holes and cascade nucleosynthesis constrain this scenario. Comment: 9 pages, 6 eps figures; v2: 7 yr WMAP data included, to appear in PRD
02/2010;
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ABSTRACT: An analytic solution for the accretion of ultrahard perfect fluid onto a moving Kerr-Newman black hole is found. This solution is a generalization of the previously known solution by Petrich, Shapiro, and Teukolsky for a Kerr black hole. We show that the found solution is applicable for the case of a nonextreme black hole, however it cannot describe the accretion onto an extreme black hole due to violation of the test fluid approximation. We also present a stationary solution for a massless scalar field in the metric of a Kerr-Newman naked singularity.
Phys. Rev. D. 11/2008; 78(10).
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ABSTRACT: An analytic solution for the accretion of ultra-hard perfect fluid onto a moving Kerr-Newman black hole is found. This solution is a generalization of the previously known solution by Petrich, Shapiro and Teukolsky for a Kerr black hole. Our solution is not applicable for an extreme black hole due to violation of the test fluid approximation. We also present a stationary solution for a massless scalar field in the metric of a Kerr-Newman naked singularity.
08/2008;
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ABSTRACT: The stationary, spherically symmetric accretion of dark energy onto a Schwarzschild black hole is considered in terms of relativistic hydrodynamics. The approximation of an ideal fluid is used to model the dark energy. General expressions are derived for the accretion rate of an ideal fluid with an arbitrary equation of state p=p(\rho) onto a black hole. The black hole mass was found to decrease for the accretion of phantom energy. The accretion process is studied in detail for two dark energy models that admit an analytical solution: a model with a linear equation of state, p=\alpha(\rho-\rho_0), and a Chaplygin gas. For one of the special cases of a linear equation of state, an analytical expression is derived for the accretion rate of dark energy onto a moving and rotating black hole. The masses of all black holes are shown to approach zero in cosmological models with phantom energy in which the Big Rip scenario is realized. Comment: 16 pages, 4 figures
05/2005;
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ABSTRACT: We describe the possible scenarios for the evolution of a thin spherically symmet-ric self-gravitating phantom shell around the Schwarzschild black hole. The general equations describing the motion of the shell with a general form of equation of state are derived and analyzed. The different types of space-time R ± -and T ± -regions and shell motion are classified depending on the parameters of the problem. It is shown that in the case of a positive shell mass there exist three scenarios for the shell evolution with an infinite motion and two distinctive types of collapse. Analo-gous scenarios were classified for the case of a negative shell mass. In particular this classification shows that it is impossible for the physical observer to detect the fan-tom energy flow. We shortly discuss the importance of our results for astrophysical applications.
04/2005; 80.
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ABSTRACT: Solution for a stationary spherically symmetric accretion of the relativistic perfect fluid with an equation of state p(rho) onto the Schwarzschild black hole is presented. This solution is a generalization of Michel solution and applicable to the problem of dark energy accretion. It is shown that accretion of phantom energy is accompanied by the gradual decrease of the black hole mass. Masses of all black holes tend to zero in the phantom energy Universe approaching the Big Rip.
Physical Review Letters 08/2004; 93(2):021102. · 7.37 Impact Factor
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ABSTRACT: Dark energy with the usually used equation of state $p=w\rho$, where $w=const<0$ is hydrodynamically unstable. To overcome this drawback we consider the cosmology of a perfect fluid with a linear equation of state of a more general form $p=\alpha(\rho-\rho_0)$, where the constants $\alpha$ and $\rho_0$ are free parameters. This non-homogeneous linear equation of state provides the description of both hydrodynamically stable ($\alpha>0$) and unstable ($\alpha<0$) fluids. In particular, the considered cosmological model describes the hydrodynamically stable dark (and phantom) energy. The possible types of cosmological scenarios in this model are determined and classified in terms of attractors and unstable points by the using of phase trajectories analysis. For the dark energy case there are possible some distinctive types of cosmological scenarios: (i) the universe with the de Sitter attractor at late times, (ii) the bouncing universe, (iii) the universe with the Big Rip and with the anti-Big Rip. In the framework of a linear equation of state the universe filled with an phantom energy, $w<-1$, may have either the de Sitter attractor or the Big Rip. Comment: 12 pages, 11 figures, typos corrected, references added
07/2004;
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ABSTRACT: Production of small-scale DM clumps is studied in the standard cosmological scenario with an inflation-produced primeval fluctuation spectrum. Special attention is given to three following problems: (i) The mass spectrum of small-scale clumps with $M \lesssim 10^3 M_{\odot}$ is calculated with tidal destruction of the clumps taken into account within the hierarchical model of clump structure. Only 0.1 - 0.5% of small clumps survive the stage of tidal destruction in each logarithmic mass interval $\Delta\ln M\sim1$. (ii) The mass distribution of clumps has a cutoff at $M_{\rm min}$ due to diffusion of DM particles out of a fluctuation and free streaming at later stage. $M_{\rm min}$ is a model dependent quantity. In the case the neutralino, considered as a pure bino, is a DM particle, $M_{\rm min} \sim 10^{-8} M_{\odot}$. (iii) The evolution of density profile in a DM clump does not result in the singularity because of formation of the core under influence of tidal interaction. The radius of the core is $R_c \sim 0.1 R$, where $R$ is radius of the clump. The applications for annihilation of DM particles in the Galactic halo are studied. The number density of clumps as a function of their mass, radius and distance to the Galactic center is presented. The enhancement of annihilation signal due to clumpiness, valid for arbitrary DM particles, is calculated. In spite of small survival probability, the annihilation signal in most cases is dominated by clumps. For observationally preferable value of index or primeval fluctuation spectrum $n_p \approx 1$, the enhancement of annihilation signal is described by factor 2 - 5 for different density profiles in a clump.
02/2003;
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ABSTRACT: We study the cosmological origin of small-scale DM clumps in the hierarchical scenario with a most conservative assumption of adiabatic gaussian fluctuations. The main included effect (tidal interaction) results in the formation of a large core in the center of a clump and in tidal destruction of a large fraction of the clumps. The enhancement of the annihilation signal due to DM clumpiness in the galactic halo, valid for arbitrary DM particles, is calculated.
Nuclear Physics B - Proceedings Supplements 138:25-27. · 0.88 Impact Factor
