Yu. N. Eroshenko

Black Hole Mass Decreasing due to Phantom Energy Accretion

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.

Dark energy cosmology with generalized linear equation of state

Dark energy with the usually used equation of state p = wp, where w = const 0) and unstable (a < 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 using phase trajectories analysis. For the dark energy case, some distinctive types of cosmological scenarios are possible: (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 a phantom energy, w < -1; may have either the de Sitter attractor or the big rip.

The accretion of dark energy onto a black hole

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(ρ) 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 = α(ρ − ρ0), 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.

ULTRAHARD FLUID AND SCALAR FIELD IN THE KERR-NEWMAN METRIC

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.

Perfect fluid and scalar field in the Reissner-Nordstrom metric

We describe the spherically symmetric steady-state accretion of perfect fluid in the Reissner-Nordström metric. We present analytic solutions for accretion of a fluid with linear equations of state and of the Chaplygin gas. We also show that under reasonable physical conditions, there is no steady-state accretion of a perfect fluid onto a Reissner-Nordström naked singularity. Instead, a static atmosphere of fluid is formed. We discuss a possibility of violation of the third law of black hole thermodynamics for a phantom fluid accretion.

Superdense cosmological dark matter clumps

V. Berezinsky, 2, 3 V. Dokuchaev, 3 Yu. Eroshenko, 3 M. Kachelrieß, and M. Aa. Solberg INFN, Laboratori Nazionali del Gran Sasso, I–67010 Assergi (AQ), Italy Center for Astroparticle Physics at LNGS (CFA), I–67010 Assergi (AQ), Italy Institute for Nuclear Research of the Russian Academy of Sciences, Moscow, Russia Institutt for fysikk, NTNU Trondheim, N–7491 Trondheim, Norway (Dated: February 18, 2010)

Early formation of galaxies induced by clusters of black holes

A model for the formation of supermassive black holes at the center of a cluster of primordial black holes is developed. It is assumed that ∼10−3 of the mass of the Universe consists of compact clusters of primordial black holes that arose as a result of phase transitions in the early Universe. These clusters also serve as centers for the condensation of dark matter. The formation of protogalaxies with masses of the order of 2 × 108M⊙ at redshift z = 15 containing clusters of black holes is investigated. The nuclei of these protogalaxies contain central black holes with masses ∼105M⊙, and the protogalaxies themselves resemble dwarf spherical galaxies with their maximum density at their centers. Subsequent merging of these induced protogalaxies with ordinary halos of dark matter leads to the standard picture for the formation of the large-scale structure of the Universe. The merging of the primordial black holes leads to the formation of supermassive black holes in galactic nuclei and produces the observed correlation between the mass of the central black hole and the bulge velocity dispersion.

Gamma-Ray Bursts from Evolved Galactic Nuclei

A new cosmological scenario for the origin of gamma-ray bursts (GRBs) is proposed. In our scenario, a highly evolved central core in the dense galactic nucleus is formed, containing a subsystem of compact stellar remnants (CSRs), such as neutron stars and black holes. Those subsystems result from the dynamical evolution of dense central stellar clusters in the galactic nuclei through merging of stars, thereby forming (as has been realized by many authors) the short-lived massive stars and then CSRs. We estimate the rate of random CSR collisions in the evolved galactic nuclei by taking into account, in a procedure similar to that of Quinlan & Shapiro, the dissipative encounters of CSRs, mainly due to radiative losses of gravitational waves, which result in the formation of intermediate short-lived binaries, with further coalescence of the companions to produce GRBs. We also consider how the possible presence of a central supermassive black hole, formed in a highly evolved galactic nucleus, influences the CSR binary formation. This scenario does not postulate ad hoc a required number of tight binary neutron stars in the galaxies. Instead, it gives, for the most realistic parameters of the evolved nuclei, the expected rate of GRBs consistent with the observed one, thereby explaining the GRB appearance as a natural part of the dynamical evolution of galactic nuclei. In addition, this scenario provides an opportunity for a cosmological GRB recurrence, previously considered to be a distinctive feature of GRBs of a local origin only. We also discuss some other observational tests of the proposed scenario.

Formation and internal structure of superdense dark matter clumps and ultracompact minihaloes

We discuss the formation mechanisms and structure of the superdense dark matter clumps (SDMC) and ultracompact minihaloes (UCMH), outlining the differences between these types of DM objects. We define as SDMC the gravitationally bounded DM objects which have come into virial equilibrium at the radiation-dominated (RD) stage of the universe evolution. Such objects can be formed from the isocurvature (entropy) density perturbations or from the peaks in the spectrum of curvature (adiabatic) perturbation. The axion miniclusters (Kolb and Tkachev 1994) are the example of the former model. The system of central compact mass (e.g. in the form of SDMC or primordial black hole (PBH)) with the outer DM envelope formed in the process of secondary accretion we refer to as UCMH. Therefore, the SDMC can serve as the seed for the UCMH in some scenarios. Recently, the SDMC and UCMH were considered in the many works, and we try to systematize them here. We consider also the effect of asphericity of the initial density perturbation in the gravitational evolution, which decreases the SDMC amount and, as the result, suppresses the gamma-ray signal from DM annihilation.

ORIGIN OF CORRELATIONS BETWEEN CENTRAL BLACK-HOLE MASSES AND GALACTIC BULGE VELOCITY DISPERSIONS

We argue that the observed correlations between central black-hole masses M BH and Galactic bulge velocity dispersions σe in the form M BH ∝ σ4 c may witness the pre-Galactic origin of massive black holes. Primordial black holes would be the centres for growing protogalaxies which experienced multiple mergers with ordinary galaxies. This process is accompanied by the merging of black holes in the galactic nuclei.