67 research outputs found
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
Nonradial oscillations of quark stars
Recently, it has been reported that a candidate for a quark star may have
been observed. In this article, we pay attention to quark stars with radiation
radii in the reported range. We calculate nonradial oscillations of -, -
and -modes. Then, we find that the dependence of the -mode
quasi-normal frequency on the bag constant and stellar radiation radius is very
strong and different from that of the lowest -mode quasi-normal
frequency. Furthermore we deduce a new empirical formula between the -mode
frequency of gravitational waves and the parameter of the equation of state for
quark stars. The observation of gravitational waves both of the -mode and of
the lowest -mode would provide a powerful probe for the equation of
state of quark matter and the properties of quark stars.Comment: 13 pages, 6 figures, accepted for publication in Phys.Rev.
Asymptotic quasinormal modes of Reissner-Nordstr\"om and Kerr black holes
According to a recent proposal, the so-called Barbero-Immirzi parameter of
Loop Quantum Gravity can be fixed, using Bohr's correspondence principle, from
a knowledge of highly-damped black hole oscillation frequencies. Such
frequencies are rather difficult to compute, even for Schwarzschild black
holes. However, it is now quite likely that they may provide a fundamental link
between classical general relativity and quantum theories of gravity. Here we
carry out the first numerical computation of very highly damped quasinormal
modes (QNM's) for charged and rotating black holes. In the Reissner-Nordstr\"om
case QNM frequencies and damping times show an oscillatory behaviour as a
function of charge. The oscillations become faster as the mode order increases.
At fixed mode order, QNM's describe spirals in the complex plane as the charge
is increased, tending towards a well defined limit as the hole becomes
extremal. Kerr QNM's have a similar oscillatory behaviour when the angular
index . For the real part of Kerr QNM frequencies tends to
, being the angular velocity of the black hole horizon, while
the asymptotic spacing of the imaginary parts is given by .Comment: 13 pages, 7 figures. Added result on the asymptotic spacing of the
imaginary part, minor typos correcte
Scattering of particles by neutron stars: Time-evolutions for axial perturbations
The excitation of the axial quasi-normal modes of a relativistic star by
scattered particles is studied by evolving the time dependent perturbation
equations. This work is the first step towards the understanding of more
complicated perturbative processes, like the capture or the scattering of
particles by rotating stars. In addition, it may serve as a test for the
results of the full nonlinear evolution of binary systems.Comment: 7 pages, 5 figures, Phys. Rev. D in pres
Numerical simulation of the massive scalar field evolution in the Reissner-Nordstr\"{o}m black hole background
We studied the massive scalar wave propagation in the background of
Reissner-Nordstr\"{o}m black hole by using numerical simulations. We learned
that the value plays an important role in determining the properties of
the relaxation of the perturbation. For the relaxation process
depends only on the field parameter and does not depend on the spacetime
parameters. For , the dependence of the relaxation on the black hole
parameters appears. The bigger mass of the black hole, the faster the
perturbation decays. The difference of the relaxation process caused by the
black hole charge has also been exhibited.Comment: Accepted for publication in Phys. Rev.
Highly damped quasinormal modes of Kerr black holes
Motivated by recent suggestions that highly damped black hole quasinormal
modes (QNM's) may provide a link between classical general relativity and
quantum gravity, we present an extensive computation of highly damped QNM's of
Kerr black holes. We do not limit our attention to gravitational modes, thus
filling some gaps in the existing literature. The frequency of gravitational
modes with l=m=2 tends to \omega_R=2 \Omega, \Omega being the angular velocity
of the black hole horizon. If Hod's conjecture is valid, this asymptotic
behaviour is related to reversible black hole transformations. Other highly
damped modes with m>0 that we computed do not show a similar behaviour. The
real part of modes with l=2 and m<0 seems to asymptotically approach a constant
value \omega_R\simeq -m\varpi, \varpi\simeq 0.12 being (almost) independent of
a. For any perturbing field, trajectories in the complex plane of QNM's with
m=0 show a spiralling behaviour, similar to the one observed for
Reissner-Nordstrom (RN) black holes. Finally, for any perturbing field, the
asymptotic separation in the imaginary part of consecutive modes with m>0 is
given by 2\pi T_H (T_H being the black hole temperature). We conjecture that
for all values of l and m>0 there is an infinity of modes tending to the
critical frequency for superradiance (\omega_R=m) in the extremal limit.
Finally, we study in some detail modes branching off the so--called
``algebraically special frequency'' of Schwarzschild black holes. For the first
time we find numerically that QNM multiplets emerge from the algebraically
special Schwarzschild modes, confirming a recent speculation.Comment: 19 pages, 11 figures. Minor typos corrected. Updated references to
take into account some recent development
Dynamical evolution and leading order gravitational wave emission of Riemann-S binaries
An approximate strategy for studying the evolution of binary systems of
extended objects is introduced. The stars are assumed to be polytropic
ellipsoids. The surfaces of constant density maintain their ellipsoidal shape
during the time evolution. The equations of hydrodynamics then reduce to a
system of ordinary differential equations for the internal velocities, the
principal axes of the stars and the orbital parameters. The equations of motion
are given within Lagrangian and Hamiltonian formalism. The special case when
both stars are axially symmetric fluid configurations is considered. Leading
order gravitational radiation reaction is incorporated, where the quasi-static
approximation is applied to the internal degrees of freedom of the stars. The
influence of the stellar parameters, in particular the influence of the
polytropic index , on the leading order gravitational waveforms is studied.Comment: 31 pages, 7 figures, typos correcte
Quasi-normal Modes of Electromagnetic Perturbations of Four-Dimensional Topological Black Holes with Scalar Hair
We study the perturbative behaviour of topological black holes with scalar
hair. We calculate both analytically and numerically the quasi-normal modes of
the electromagnetic perturbations. In the case of small black holes we find
evidence of a second-order phase transition of a topological black hole to a
hairy configuration.Comment: v2: 19 pages, 2 figures, added references, improved discussion, to
appear in JHE
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