159 research outputs found
Gravitational Waves from Compact Sources
We review sources of high-frequency gravitational waves, summarizing our
current understanding of emission mechanisms, expected amplitudes and event
rates. The most promising sources are gravitational collapse (formation of
black holes or neutron stars) and subsequent ringing of the compact star,
secular or dynamical rotational instabilities and high-mass compact objects
formed through the merger of binary neutron stars. Significant and unique
information for the various stages of the collapse, the structure of
protoneutron stars and the high density equation of state of compact objects
can be drawn from careful study of gravitational wave signals.Comment: 22 pages, Proceedings of the 5th International Workshop "New Worlds
in Astroparticle Physics", Faro, Portugal, 8-10 January 200
TIDAL AND TIDAL-RESONANT EFFECTS IN COALESCING BINARIES
Tidal and tidal-resonant effects in coalescing compact binary systems are
investigated by direct numerical integration of the equations of motion. For
the stars polytropic models are used. The tidal effects are found to be
dominated by the (non-resonant) -modes. The effect of the -mode-tidal
resonances is obtained. The tidal interaction is shown to be of interest
especially for low-mass binaries. There exists a characteristic final plunge
orbit beyond which the system cannot remain stable even if radiation reaction
is not taken into account; in agreement with results obtained by Lai et al.
\shortcite{Lai93}. The importance of the investigated effects for the
observation of gravitational waves on Earth is discussed.Comment: 17 pages, latex (mn.sty), 5 figures, M.N.R.A.S. in pres
A Semi-analytic Study of Axial Perturbations of Ultra Compact Stars
Compact object perturbations, at linear order, often lead in solving one or
more coupled wave equations. The study of these equations was typically done by
numerical or semi-analytical methods. The WKB method and the associated
Bohr-Sommerfeld rule have been proved extremely useful tools in the study of
black-hole perturbations and the estimation of the related quasi-normal modes.
Here we present an extension of the aforementioned semi-analytic methods in the
study of perturbations of ultra-compact stars and gravastars.Comment: Accepted for publication in CQG, 13 pages, 3 figures, 5 table
The Photon Spectrum of Asymmetric Dark Stars
Asymmetric Dark Stars, i.e., compact objects formed from the collapse of
asymmetric dark matter could potentially produce a detectable photon flux if
dark matter particles self-interact via dark photons that kinetically mix with
ordinary photons. The morphology of the emitted spectrum is significantly
different and therefore distinguishable from a typical black-body one. Given
the above and the fact that asymmetric dark stars can have masses outside the
range of neutron stars, the detection of such a spectrum can be considered as a
smoking gun signature for the existence of these exotic stars.Comment: Minor changes to match the version published on IJMP
The stochastic background of gravitational waves due to the f-mode instability in neutron stars
This paper presents an estimate for the spectral properties of the stochastic
background of gravitational waves emitted by a population of hot, young,
rapidly rotating neutron stars throughout the Universe undergoing -mode
instabilities, formed through either core-collapse supernova explosions or the
merger of binary neutron star systems. Their formation rate, from which the
gravitational wave event rate is obtained, is deduced from observation-based
determinations of the cosmic star formation rate. The gravitational wave
emission occurs during the spin-down phase of the -mode instability. For low
magnetized neutron stars and assuming 10\% of supernova events lead to -mode
unstable neutron stars, the background from supernova-derived neutron stars
peaks at for the -mode, which
should be detectable by cross-correlating a pair of second generation
interferometers (e.g. Advanced LIGO/Virgo) with an upper estimate for the
signal-to-noise ratio of 9.8. The background from supramassive
neutron stars formed from binary mergers peaks at and should not be detectable, even with third generation
interferometers (e.g. Einstein Telescope)
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