126 research outputs found
GRB Redshift Distribution is Consistent with GRB Origin in Evolved Galactic Nuclei
Recently we have elaborated a new cosmological model of gamma-ray burst (GRB)
origin (1998, ApJ 502, 192), which employs the dynamical evolution of central
dense stellar clusters in the galactic nuclei. Those clusters inevitably
contain a large fraction of compact stellar remnants (CSRs), such as neutron
stars (NSs) and stellar mass black holes (BHs), and close encounters between
them result in radiative captures into short-living binaries, with subsequent
merging of the components, thereby producing GRBs (typically at large distances
from the nucleus).
In the present paper, we calculate the redshift distribution of the rate of
GRBs produced by close encounters of NSs in distant galactic nuclei. To this
end, the following steps are undertaken: (i) we establish a connection between
the parameters of the fast evolving central stellar clusters (i.e. those for
which the time of dynamical evolution exceeds the age of the Universe) with
masses of the forming central supermassive black holes (SMBHs) using a
dynamical evolution model; (ii) we connect these masses with the inferred mass
distributions of SMBHs in the galactic nuclei and the redshift distribution of
quasars by assuming a certain `Eddington luminosity phase' in their activity;
(iii) we incorporate available observational data on the redshift distribution
of quasars as well as a recently found correlation between the masses of
galaxies and their central SMBHs. The resulting redshift distribution of the
GRB rate, which accounts for both fast and slowly evolving galactic nuclei is
consistent with that inferred from the BATSE data if the fraction of fast
evolving galactic nuclei is in the range .Comment: LaTeX, 4 pages (incl. 1 figure), to appear in "After the Dark Ages:
When Galaxies Were Young (the Universe at 2<z<5)", eds. S.S. Holt and E.P.
Smit
The Eddington Luminosity Phase in Quasars: Duration and Implications
Non-steady and eruptive phenomena in quasars are thought to be associated
with the Eddington or super-Eddington luminous stage. Although there is no lack
in hypotheses about the total duration of such a stage, the latter remains
essentially unknown. We calculate the duration of quasar luminous phase in
dependence upon the initial mass of a newborn massive black hole (MBH) by
comparing the observed luminosity- and redshift distributions of quasars with
mass distribution of the central MBHs in normal galactic nuclei. It is assumed
that, at the quasar stage, each MBH goes through a single (or recurrent)
phase(s) of accretion with, or close to, the Eddington luminosity. The mass
distributions of quasars is found to be connected with that of MBHs residing in
normal galaxies by a one-to-one corrrespondence through the entire mass range
of the inferred MBHs if the accretion efficiency of mass-to-energy
transformation .Comment: 4 pages, 2 figures, uses aipproc.sty. To appear in "Cosmic
Explosions" (Proc. of the 10th Annual October Conference in Maryland, Eds.
S.S. Holt and W.W. Zhang
Vacuum shell in the Schwarzschild-de Sitter world
We construct the classification scheme for all possible evolution scenarios
and find the corresponding global geometries for dynamics of a thin spherical
vacuum shell in the Schwarzschild-de Sitter metric. This configuration is
suitable for the modelling of vacuum bubbles arising during cosmological phase
transitions in the early Universe. The distinctive final types of evolution
from the local point of view of a rather distant observer are either the
unlimited expansion of the shell or its contraction with a formation of black
hole (with a central singularity) or wormhole (with a baby universe in
interior).Comment: 15 pages, 8 figure
Mechanism for the Suppression of Intermediate-Mass Black Holes
A model for the formation of supermassive primordial black holes in galactic
nuclei with the simultaneous suppression of the formation of intermediate-mass
black holes is presented. A bimodal mass function for black holes formed
through phase transitions in a model with a "Mexican hat" potential has been
found. The classical motion of the phase of a complex scalar field during
inflation has been taken into account. Possible observational manifestations of
primordial black holes in galaxies and constraints on their number are
discussed.Comment: 12 pages, 2 figure
Gamma Ray Bursts from the 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-living massive stars and then CSRs. We estimate the rate of
random CSR collisions in the evolved galactic nuclei by taking into account,
similar to Quinlan & Shapiro (1987), the dissipative encounters of CSRs, mainly
due to radiative losses of gravitational waves, which results in the formation
of intermediate short-living 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 in a natural way 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.Comment: 25 pages, LATEX, uses aasms4.sty, accepted by Ap
Swift J164449.3+573451 event: generation in the collapsing star cluster?
We discuss the multiband energy release in a model of a collapsing galactic
nucleus, and we try to interpret the unique super-long cosmic gamma-ray event
Swift J164449.3+573451 (GRB 110328A by early classification) in this scenario.
Neutron stars and stellar-mass black holes can form evolutionary a compact
self-gravitating subsystem in the galactic center. Collisions and merges of
these stellar remnants during an avalanche contraction and collapse of the
cluster core can produce powerful events in different bands due to several
mechanisms. Collisions of neutron stars and stellar-mass black holes can
generate gamma-ray bursts (GRBs) similar to the ordinary models of short GRB
origin. The bright peaks during the first two days may also be a consequence of
multiple matter supply (due to matter release in the collisions) and accretion
onto the forming supermassive black hole. Numerous smaller peaks and later
quasi-steady radiation can arise from gravitational lensing, late accretion of
gas onto the supermassive black hole, and from particle acceleration by shock
waves. Even if this model will not reproduce exactly all the Swift
J164449.3+573451 properties in future observations, such collapses of galactic
nuclei can be available for detection in other events.Comment: 7 pages, replaced by the final versio
Dynamical Friction of a Circular-Orbit Perturber in a Gaseous Medium
We investigate the gravitational wake due to, and dynamical friction on, a
perturber moving on a circular orbit in a uniform gaseous medium using a
semi-analytic method. This work is a straightforward extension of Ostriker
(1999) who studied the case of a straight-line trajectory. The circular orbit
causes the bending of the wake in the background medium along the orbit,
forming a long trailing tail. The wake distribution is thus asymmetric, giving
rise to the drag forces in both opposite (azimuthal) and lateral (radial)
directions to the motion of the perturber, although the latter does not
contribute to orbital decay much. For subsonic motion, the density wake with a
weak tail is simply a curved version of that in Ostriker and does not exhibit
the front-back symmetry. The resulting drag force in the opposite direction is
remarkably similar to the finite-time, linear-trajectory counterpart. On the
other hand, a supersonic perturber is able to overtake its own wake, possibly
multiple times, and develops a very pronounced tail. The supersonic tail
surrounds the perturber in a trailing spiral fashion, enhancing the perturbed
density at the back as well as far front of the perturber. We provide the
fitting formulae for the drag forces as functions of the Mach number, whose
azimuthal part is surprisingly in good agreement with the Ostriker's formula,
provided Vp t=2 Rp, where Vp and Rp are the velocity and orbital radius of the
perturber, respectively.Comment: 28 pages, 9 figures, accepted for publication in Astrophysical
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