837 research outputs found
Oscillations of rapidly rotating relativistic stars
Non-axisymmetric oscillations of rapidly rotating relativistic stars are
studied using the Cowling approximation. The oscillation spectra have been
estimated by Fourier transforming the evolution equations describing the
perturbations. This is the first study of its kind and provides information on
the effect of fast rotation on the oscillation spectra while it offers the
possibility in studying the complete problem by including spacetime
perturbations. Our study includes both axisymmetric and non-axisymmetric
perturbations and provides limits for the onset of the secular bar mode
rotational instability. We also present approximate formulae for the dependence
of the oscillation spectrum from rotation. The results suggest that it is
possible to extract the relativistic star's parameters from the observed
gravitational wave spectrum.Comment: this article will be published in Physical Review
A geometric framework for black hole perturbations
Black hole perturbation theory is typically studied on time surfaces that
extend between the bifurcation sphere and spatial infinity. From a physical
point of view, however, it may be favorable to employ time surfaces that extend
between the future event horizon and future null infinity. This framework
resolves problems regarding the representation of quasinormal mode
eigenfunctions and the construction of short-ranged potentials for the
perturbation equations in frequency domain.Comment: 4 pages, 1 figur
Instabilities of Relativistic Stars
Recent developments on the rotational instabilities of relativistic stars are
reviewed. The article provides an account of the theory of stellar
instabilities with emphasis on the rotational ones. Special attention is being
paid to the study of these instabilities in the general relativistic regime.
Issues such as the existence relativistic r-modes, the existence of a
continuous spectrum and the CFS instability of the w-modes are discussed in the
second half of the article.Comment: 41 pages, 12 figures, Proceedings of the 25th John Hopkins Workshop,
Florenc
High frequency sources of gravitational waves
Sources of high frequency gravitational waves are reviewed. Gravitational
collapse, rotational instabilities and oscillations of the remnant compact
objects are potentially important sources of gravitational waves. Significant
and unique information for the various stages of the collapse, the evolution of
protoneutron stars and the details of the equations of state of such objects
can be drawn from careful study of the gravitational wave signal.Comment: 7 pages, Class. Quantum Grav. in press. Proceedings of the 5th Amaldi
Conferenc
Analytic description of the r-mode instability in uniform density stars
We present an analytic description of the -mode instability in newly-born
neutron stars, using the approximation of uniform density. Our computation is
consistently accurate to second order in the angular velocity of the star. We
obtain formulae for the growth-time of the instability due to
gravitational-wave emission, for both current and mass multipole radiation and
for the damping timescale, due to viscosity. The current-multipole
radiation dominates the timescale of the instability. We estimate the deviation
of the second order accurate results from the lowest order approximation and
show that the uncertainty in the equation of state has only a small effect on
the onset of the -mode instability. The viscosity coefficients and the
cooling process in newly-born neutron stars are, at present, uncertain and our
analytic formaulae enables a quick check of such effects on the development of
the instability.Comment: 7 pages, 2 figure
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
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