51 research outputs found
Rapidly rotating neutron star progenitors
Rotating proto-neutron stars can be important sources of gravitational waves
to be searched for by present-day and future interferometric detectors. It was
demonstrated by Imshennik that in extreme cases the rapid rotation of a
collapsing stellar core may lead to fission and formation of a binary
proto-neutron star which subsequently merges due to gravitational wave
emission. In the present paper, we show that such dynamically unstable
collapsing stellar cores may be the product of a former merger process of two
stellar cores in a common envelope. We applied population synthesis
calculations to assess the expected fraction of such rapidly rotating stellar
cores which may lead to fission and formation of a pair of proto-neutron stars.
We have used the BSE population synthesis code supplemented with a new
treatment of stellar core rotation during the evolution via effective
core-envelope coupling, characterized by the coupling time, . The
validity of this approach is checked by direct MESA calculations of the
evolution of a rotating 15 star. From comparison of the calculated
spin distribution of young neutron stars with the observed one, reported by
Popov and Turolla, we infer the value years. We
show that merging of stellar cores in common envelopes can lead to collapses
with dynamically unstable proto-neutron stars, with their formation rate being
of the total core collapses, depending on the common envelope
efficiency.Comment: 10 pages, 4 figures, accepted for publication in MNRA
Magnetic fileds of coalescing neutron stars and the luminosity function of short gamma-ray burst
Coalescing neutron star binaries are believed to be the most reliable sources
for ground-based detectors of gravitational waves and likely progenitors of
short gamma-ray bursts. In the process of coalescence, magnetic fields of
neutron stars can induce interesting observational manifestations and affect
the form of gravitational wave signal. In this papaer we use the population
synthesis method to model the expected distribution of neutron star magnetic
fields during the coalescence under different assumptions on the initial
parameters of neutron stars and their magnetic field evolution. We discuss
possible elecotrmagnetic phenomena preceding the coalescence of magnetized
neutron star binaries and the effect of magnetic field on the gravitational
wave signal. We find that a log-normal (Gaussian in logarithms) distribution of
the initial magnetic fields of neutron stars, which agrees with observed
properties of radio pulsars, produces the distribution of the magnetic field
energy during the coalescence that adequately describes the observed luminosity
function of short gamma-ray bursts under different assumptions on the field
evolution and initial parameters of neutron stars. This agreement lends further
support to the model of coalescing neutron star binaries as progenitors of
gamma-ray bursts.Comment: v.2, LATEX, 25 pages, inc. 7 ps figures, Astron. Lett., in press.
Typos corrected, reference adde
The origin of intergalactic thermonuclear supernovae
The population synthesis method is used to study the possibility of
explaining the appreciable fraction (20^+12_15%) of the intergalactic (no-host)
type Ia supernovae observed in galaxy clusters (Gal-Yam ete al. 2003) by binary
whote dwarf merginngs in the cores of globular clusters. In a typical globular
cluster, the number of merging double white dwarfs is fount to be smaller than
10^{-13} per year per average cluster star during the entire evolution of the
cluster, which is a factor of 3 higher than in a Milky-Way-type galaxy. From 5
to 30% of the merging white dwarfs are dynamically expelled from the cluster
with barycenter velocities up to 150 km/s. SN Ia explosions during the mergers
of binary white dwarfs in dense star clusters may account for \sim 1% of the
total rate of SN Ia in the central parts of galaxy clusters if the baryon mass
fraction in such star clusters is \sim 0.3%.Comment: 8 pages, 3 figs. Astronomy Letters (in press
Broad-band gravitational-wave pulses from binary neutron stars in eccentric orbits
Maximum gravitational wave emission from binary stars in eccentric orbits
occurs near the periastron passage. We show that for a stationary distribution
of binary neutron stars in the Galaxy, several high-eccentricity systems with
orbital periods in the range from tens of minutes to several days should exist
that emit broad gravitational-wave pulses in the frequency range 1-100 mHz. The
space interferometer LISA could register the pulsed signal from these system at
a signal-to-noise ratio level in the frequency range Hz during one-year observational time. Some detection
algorithms for such a signal are discussed.Comment: 17 pages, LATEX, 3 figures, Astronomy Letters, 2002, in press; typos
corrected, refference adde
Life-history innovation to climate change:Can single-brooded migrant birds become multiple breeders?
When climatic conditions change and become outside the range experienced in the past, species may show life-history innovations allowing them to adapt in new ways. We report such an innovation for pied flycatchers Ficedula hypoleuca. Decades of breeding biological studies on pied flycatchers have rarely reported multiple breeding in this long-distance migrant. In two populations, we found 12 recent incidents of females with second broods, all produced by extremely early laying females in warm springs. As such early first broods are a recent phenomenon, because laying dates have gradually advanced over time, this innovation now allows individual females to enhance their reproductive success considerably. If laying dates continue advancing, potentially more females may become multiple breeders and selection for early (and multiple) breeding phenotypes increases, which may accelerate adaptation to climatic change
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
The Evolution of Compact Binary Star Systems
We review the formation and evolution of compact binary stars consisting of
white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and
BHs are thought to be the primary astrophysical sources of gravitational waves
(GWs) within the frequency band of ground-based detectors, while compact
binaries of WDs are important sources of GWs at lower frequencies to be covered
by space interferometers (LISA). Major uncertainties in the current
understanding of properties of NSs and BHs most relevant to the GW studies are
discussed, including the treatment of the natal kicks which compact stellar
remnants acquire during the core collapse of massive stars and the common
envelope phase of binary evolution. We discuss the coalescence rates of binary
NSs and BHs and prospects for their detections, the formation and evolution of
binary WDs and their observational manifestations. Special attention is given
to AM CVn-stars -- compact binaries in which the Roche lobe is filled by
another WD or a low-mass partially degenerate helium-star, as these stars are
thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure
Laser-induced modification of the patellar ligament tissue: comparative study of structural and optical changes
The effects of non-ablative infrared (IR) laser treatment of collagenous tissue have been commonly interpreted in terms of collagen denaturation spread over the laser-heated tissue area. In this work, the existing model is refined to account for the recently reported laser-treated tissue heterogeneity and complex collagen degradation pattern using comprehensive optical imaging and calorimetry toolkits. Patella ligament (PL) provided a simple model of type I collagen tissue containing its full structural content from triple-helix molecules to gross architecture. PL ex vivo was subjected to IR laser treatments (laser spot, 1.6 mm) of equal dose, where the tissue temperature reached the collagen denaturation temperature of 60 ± 2°C at the laser spot epicenterin the first regime, and was limited to 67 ± 2°C in the second regime. The collagen network was analyzed versus distance from the epicenter. Experimental characterization of the collagenous tissue at all structural levels included cross-polarization optical coherence tomography, nonlinear optical microscopy, light microscopy/histology, and differential scanning calorimetry. Regressive rearrangement of the PL collagen network was found to spread well outside the laser spot epicenter (>2 mm) and was accompanied by multilevel hierarchical reorganization of collagen. Four zones of distinct optical and morphological properties were identified, all elliptical in shape, and elongated in the direction perpendicular to the PL long axis. Although the collagen transformation into a random-coil molecular structure was occasionally observed, it was mechanical integrity of the supramolecular structures that was primarily compromised. We found that the structural rearrangement of the collagen network related primarily to the heat-induced thermo-mechanical effects rather than molecular unfolding. The current body of evidence supports the notion that the supramolecular collagen structure suffered degradation of various degrees, which gave rise to the observed zonal character of the laser-treated lesion
Gravitational Wave Astronomy: in Anticipation of First Sources to be Detected
The first generation of long-baseline laser interferometric detectors of
gravitational waves will start collecting data in 2001-2003. We carefully
analyse their planned performance and compare it with the expected strengths of
astrophysical sources. The scientific importance of the anticipated discovery
of various gravitatinal wave signals and the reliability of theoretical
predictions are taken into account in our analysis. We try to be conservative
both in evaluating the theoretical uncertainties about a source and the
prospects of its detection. After having considered many possible sources, we
place our emphasis on (1) inspiraling binaries consisting of stellar mass black
holes and (2) relic gravitational waves. We draw the conclusion that
inspiraling binary black holes are likely to be detected first by the initial
ground-based interferometers. We estimate that the initial interferometers will
see 2-3 events per year from black hole binaries with component masses
10-15M_\odot, with a signal-to-noise ratio of around 2-3, in each of a network
of detectors consisting of GEO, VIRGO and the two LIGOs. It appears that other
possible sources, including coalescing neutron stars, are unlikely to be
detected by the initial instruments. We also argue that relic gravitational
waves may be discovered by the space-based interferometers in the frequency
interval 2x10^{-3}-10^{-2} Hz, at the signal-to-noise ratio level around 3.Comment: latex, 100 pages, including 20 postscript figures. Small typos
corrected, references adde
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