127 research outputs found
Regularity of a inverse problem for generic parabolic equations
The paper studies some inverse boundary value problem for simplest parabolic
equations such that the homogenuous Cauchy condition is ill posed at initial
time. Some regularity of the solution is established for a wide class of
boundary value inputs.Comment: 9 page
The wave function of a gravitating shell
We have calculated a discrete spectrum and found an exact analytical solution
in the form of Meixner polynomials for the wave function of a thin gravitating
shell in the Reissner-Nordstrom geometry. We show that there is no extreme
state in the quantum spectrum of the gravitating shell, as in the case of
extreme black hole.Comment: 7 pages, 1 figur
Calorimetry of gamma-ray bursts: echos in gravitational waves
Black holes surrounded by a disk or torus may drive the enigmatic
cosmological gamma-ray bursts (GRBs). Equivalence in poloidal topology to
pulsar magnetospheres shows a high incidence of the black hole-luminosity
into the surrounding magnetized matter. We argue that this emission is
re-radiated into gravitational waves at in frequencies of
order 1kHz, winds and, potentially, MeV neutrinos. The total energy budget and
input to the GRB from baryon poor jets are expected to be standard in this
scenario, consistent with recent analysis of afterglow data. Collimation of
these outflows by baryon rich disk or torus winds may account for the observed
spread in opening angles up to about . This model may be tested by future
LIGO/VIRGO observations.Comment: To appear in ApJ
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
Gravitational radiation from rotating monopole-string systems
We study the gravitational radiation from a rotating monopole-antimonopole
pair connected by a string. While at not too high frequencies the emitted
gravitational spectrum is described asymptotically by , the
spectrum is exponentially suppressed in the high-frequency limit, . Below , the emitted spectrum of gravitational
waves is very similar to the case of an oscillating monopole pair connected by
a string, and we argue therefore that the spectrum found holds approximately
for any moving monopole-string system. As application, we discuss the
stochastic gravitational wave background generated by monopole-antimonopole
pairs connected by strings in the early Universe and gravitational wave bursts
emitted at present by monopole-string networks. We confirm that advanced
gravitational wave detectors have the potential to detect a signal for string
tensions as small as .Comment: 8 pages, 2 figures, revtex4; v2: minor corrections, matches published
versio
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
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
Journa
Supernovae - Optical Precursors of Short Gamma-Ray Bursts
The probability of observing "supernova - gamma-ray burst" (GRB) pair events
and recurrent GRBs from one galaxy in a time interval of several years has been
estimated. Supernova explosions in binary systems accompanied by the formation
of a short-lived pair of compact objects can be the sources of such events. If
a short GRB is generated during the collision of a pair, then approximately
each of ~300 short GRBs with redshift z must have an optical precursor - a
supernova in the observer's time interval <2(1+z)yr. If the supernova explosion
has the pattern of a hypernova, then a successive observation of long and short
GRBs is possible. The scenario for the generation of multiple GRBs in
collapsing galactic nuclei is also discussed.Comment: 12 pages, 1 figure; this paper has the e-precursor arXiv:1101.3298
[astro-ph.HE
Gravitational Wave Bursts from Collisions of Primordial Black Holes in Clusters
The rate of gravitational wave bursts from the mergers of massive primordial
black holes in clusters is calculated. Such clusters of black holes can be
formed through phase transitions in the early Universe. The central black holes
in clusters can serve as the seeds of supermassive black holes in galactic
nuclei. The expected burst detection rate by the LISA gravitational wave
detector is estimated.Comment: 10 pages, 2 figure
Possible types of the evolution of vacuum shells around the de Sitter space
All possible evolution scenarios of a thin vacuum shell surrounding the
spherically symmetric de Sitter space have been determined and the
corresponding global geometries have been constructed. Such configurations can
appear at the final stage of the cosmological phase transition, when isolated
regions (islands) of the old vacuum remain. The islands of the old vacuum are
absorbed by the new vacuum, expand unlimitedly, or form black holes and
wormholes depending on the sizes of the islands as well as on the density and
velocity of the shells surrounding the islands.Comment: 3 pages, 1 figur
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