97 research outputs found
Dynamical Bar-Mode Instability in Differentially Rotating Magnetized Neutron Stars
This paper presents a numerical study over a wide parameter space of the
likelihood of the dynamical bar-mode instability in differentially rotating
magnetized neutron stars. The innovative aspect of this study is the
incorporation of magnetic fields in such a context, which have thus far been
neglected in the purely hydrodynamical simulations available in the literature.
The investigation uses the Cosmos++ code which allows us to perform three
dimensional simulations on a cylindrical grid at high resolution. A sample of
Newtonian magneto-hydrodynamical simulations starting from a set of models
previously analyzed by other authors without magnetic fields has been
performed, providing estimates of the effects of magnetic fields on the
dynamical bar-mode deformation of rotating neutron stars. Overall, our results
suggest that the effect of magnetic fields are not likely to be very
significant in realistic configurations. Only in the most extreme cases are the
magnetic fields able to suppress growth of the bar mode.Comment: 12 pages, 16 figures. References added and minor edits made to match
published versio
Cosmic Microwave Background Anisotropies from the Rees-Sciama Effect in Universes
We investigate the imprint of nonlinear matter condensations on the Cosmic
Microwave Background (CMB) in cold dark matter (CDM) model
universes. We consider simulation domains ranging from Mpc to
Mpc in size. We concentrate on the secondary temperature
anisotropies induced by time varying gravitational potentials occurring after
decoupling. Specifically, we investigate the importance of the Rees-Sciama
effect due to: (1) intrinsic changes in the gravitational potential of forming,
nonlinear structures, (2) proper motion of nonlinear structures, and (3) late
time decay of gravitational potential perturbations in open universes. CMB
temperature anisotropies are obtained by numerically evolving matter
inhomogeneities and CMB photons from an early, linear epoch () to the
present, nonlinear epoch . We test the dependence and relative
importance of these secondary temperature anisotropies as a function of the
scale of the underlying matter (voids, superclusters) and as a function of
. The results of the models are compared to a
similarly executed simulation. We find that in low density
models all three sources of anisotropy could be relevant and reach levels of
. In particular, we find that for at
large scales, secondary temperature anisotropies are dominated by the decaying
potential.Comment: 20 pages + 7 figures + 4 plates, self-expanding uuencoded compressed
tar archive of postscript file
Computational Cosmology: from the Early Universe to the Large Scale Structure
In order to account for the observable Universe, any comprehensive theory or
model of cosmology must draw from many disciplines of physics, including gauge
theories of strong and weak interactions, the hydrodynamics and microphysics of
baryonic matter, electromagnetic fields, and spacetime curvature, for example.
Although it is difficult to incorporate all these physical elements into a
single complete model of our Universe, advances in computing methods and
technologies have contributed significantly towards our understanding of
cosmological models, the Universe, and astrophysical processes within them. A
sample of numerical calculations (and numerical methods) applied to specific
issues in cosmology are reviewed in this article: from the Big Bang singularity
dynamics to the fundamental interactions of gravitational waves; from the
quark-hadron phase transition to the large scale structure of the Universe. The
emphasis, although not exclusively, is on those calculations designed to test
different models of cosmology against the observed Universe.Comment: appearing, Living Reviews in Relativit
Radiation recoil from highly distorted black holes
We present results from numerical evolutions of single black holes distorted
by axisymmetric, but equatorially asymmetric, gravitational (Brill) waves. Net
radiated energies, apparent horizon embeddings, and recoil velocities are shown
for a range of Brill wave parameters, including both even and odd parity
distortions of Schwarzschild black holes. We find that a wave packet initially
concentrated on the black hole throat, a likely model also for highly
asymmetric stellar collapse and late stage binary mergers, can generate a
maximum recoil velocity of about 150 (23) km/sec for even (odd) parity
perturbations, significantly less than that required to eject black holes from
galactic cores.Comment: 15 pages, 8 figure
- …