16,058 research outputs found
A detailed study of quasinormal frequencies of the Kerr black hole
We compute the quasinormal frequencies of the Kerr black hole using a
continued fraction method. The continued fraction method first proposed by
Leaver is still the only known method stable and accurate for the numerical
determination of the Kerr quasinormal frequencies. We numerically obtain not
only the slowly but also the rapidly damped quasinormal frequencies and analyze
the peculiar behavior of these frequencies at the Kerr limit. We also calculate
the algebraically special frequency first identified by Chandrasekhar and
confirm that it coincide with the quasinormal frequency only at the
Schwarzschild limit.Comment: REVTEX, 15 pages, 7 eps figure
Asymptotically Hyperbolic Non Constant Mean Curvature Solutions of the Einstein Constraint Equations
We describe how the iterative technique used by Isenberg and Moncrief to
verify the existence of large sets of non constant mean curvature solutions of
the Einstein constraints on closed manifolds can be adapted to verify the
existence of large sets of asymptotically hyperbolic non constant mean
curvature solutions of the Einstein constraints.Comment: 19 pages, TeX, no figure
Shock propagation and stability in causal dissipative hydrodynamics
We studied the shock propagation and its stability with the causal
dissipative hydrodynamics in 1+1 dimensional systems. We show that the presence
of the usual viscosity is not enough to stabilize the solution. This problem is
solved by introducing an additional viscosity which is related to the
coarse-graining scale of the theory.Comment: 14 pages, 16 figure
A microfluidic device for the study of the orientational dynamics of microrods
We describe a microfluidic device for studying the orientational dynamics of
microrods. The device enables us to experimentally investigate the tumbling of
microrods immersed in the shear flow in a microfluidic channel with a depth of
400 mu and a width of 2.5 mm. The orientational dynamics was recorded using a
20 X microscopic objective and a CCD camera. The microrods were produced by
shearing microdroplets of photocurable epoxy resin. We show different examples
of empirically observed tumbling. On the one hand we find that short stretches
of the experimentally determined time series are well described by fits to
solutions of Jeffery's approximate equation of motion [Jeffery, Proc. R. Soc.
London. 102 (1922), 161-179]. On the other hand we find that the empirically
observed trajectories drift between different solutions of Jeffery's equation.
We discuss possible causes of this orbit drift.Comment: 11 pages, 8 figure
Line Emission from Gas in Optically Thick Dust Disks around Young Stars
We present self-consistent models of gas in optically-thick dusty disks and
calculate its thermal, density and chemical structure. The models focus on an
accurate treatment of the upper layers where line emission originates, and at
radii AU. We present results of disks around stars where we have varied dust properties, X-ray luminosities and
UV luminosities. We separately treat gas and dust thermal balance, and
calculate line luminosities at infrared and sub-millimeter wavelengths from all
transitions originating in the predominantly neutral gas that lies below the
ionized surface of the disk. We find that the [ArII] 7m, [NeII]
12.8m, [FeI] 24m, [SI] 25m, [FeII] 26m, [SiII] 35 m,
[OI] 63m and pure rotational lines of H, HO and CO can be quite
strong and are good indicators of the presence and distribution of gas in
disks. We apply our models to the disk around the nearby young star, TW Hya,
and find good agreement between our model calculations and observations. We
also predict strong emission lines from the TW Hya disk that are likely to be
detected by future facilities. A comparison of CO observations with our models
suggests that the gas disk around TW Hya may be truncated to AU,
compared to its dust disk of 174 AU. We speculate that photoevaporation due to
the strong stellar FUV field from TW Hya is responsible for the gas disk
truncation.Comment: Accepted to Astrophysical Journa
On the asymptotic behavior of static perfect fluids
Static spherically symmetric solutions to the Einstein-Euler equations with
prescribed central densities are known to exist, be unique and smooth for
reasonable equations of state. Some criteria are also available to decide
whether solutions have finite extent (stars with a vacuum exterior) or infinite
extent. In the latter case, the matter extends globally with the density
approaching zero at infinity. The asymptotic behavior largely depends on the
equation of state of the fluid and is still poorly understood. While a few such
unbounded solutions are known to be asymptotically flat with finite ADM mass,
the vast majority are not. We provide a full geometric description of the
asymptotic behavior of static spherically symmetric perfect fluid solutions
with linear and polytropic-type equations of state with index n>5. In order to
capture the asymptotic behavior we introduce a notion of scaled
quasi-asymptotic flatness, which encodes a form of asymptotic conicality. In
particular, these spacetimes are asymptotically simple.Comment: 32 pages; minor changes in v2, final versio
R-mode Instability of Slowly Rotating Non-isentropic Relativistic Stars
We investigate properties of -mode instability in slowly rotating
relativistic polytropes. Inside the star slow rotation and low frequency
formalism that was mainly developed by Kojima is employed to study axial
oscillations restored by Coriolis force. At the stellar surface, in order to
take account of gravitational radiation reaction effect, we use a near-zone
boundary condition instead of the usually imposed boundary condition for
asymptotically flat spacetime. Due to the boundary condition, complex
frequencies whose imaginary part represents secular instability are obtained
for discrete -mode oscillations in some polytropic models. It is found that
such discrete -mode solutions can be obtained only for some restricted
polytropic models. Basic properties of the solutions are similar to those
obtained by imposing the boundary condition for asymptotically flat spacetime.
Our results suggest that existence of a continuous part of spectrum cannot be
avoided even when its frequency becomes complex due to the emission of
gravitational radiation.Comment: 10 pages, 4 figures, accepted for publlication in PR
r-modes in Relativistic Superfluid Stars
We discuss the modal properties of the -modes of relativistic superfluid
neutron stars, taking account of the entrainment effects between superfluids.
In this paper, the neutron stars are assumed to be filled with neutron and
proton superfluids and the strength of the entrainment effects between the
superfluids are represented by a single parameter . We find that the
basic properties of the -modes in a relativistic superfluid star are very
similar to those found for a Newtonian superfluid star. The -modes of a
relativistic superfluid star are split into two families, ordinary fluid-like
-modes (-mode) and superfluid-like -modes (-mode). The two
superfluids counter-move for the -modes, while they co-move for the
-modes. For the -modes, the quantity is
almost independent of the entrainment parameter , where and
are the azimuthal wave number and the oscillation frequency observed by an
inertial observer at spatial infinity, respectively. For the -modes, on
the other hand, almost linearly increases with increasing . It
is also found that the radiation driven instability due to the -modes is
much weaker than that of the -modes because the matter current associated
with the axial parity perturbations almost completely vanishes.Comment: 14 pages, 4 figures. To appear in Physical Review
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