1,925 research outputs found
Excision boundary conditions for black hole initial data
We define and extensively test a set of boundary conditions that can be
applied at black hole excision surfaces when the Hamiltonian and momentum
constraints of general relativity are solved within the conformal thin-sandwich
formalism. These boundary conditions have been designed to result in black
holes that are in quasiequilibrium and are completely general in the sense that
they can be applied with any conformal three-geometry and slicing condition.
Furthermore, we show that they retain precisely the freedom to specify an
arbitrary spin on each black hole. Interestingly, we have been unable to find a
boundary condition on the lapse that can be derived from a quasiequilibrium
condition. Rather, we find evidence that the lapse boundary condition is part
of the initial temporal gauge choice. To test these boundary conditions, we
have extensively explored the case of a single black hole and the case of a
binary system of equal-mass black holes, including the computation of
quasi-circular orbits and the determination of the inner-most stable circular
orbit. Our tests show that the boundary conditions work well.Comment: 23 pages, 23 figures, revtex4, corrected typos, added reference,
minor content changes including additional post-Newtonian comparison. Version
accepted by PR
Robust evolution system for Numerical Relativity
The paper combines theoretical and applied ideas which have been previously
considered separately into a single set of evolution equations for Numerical
Relativity. New numerical ingredients are presented which avoid gauge
pathologies and allow one to perform robust 3D calculations. The potential of
the resulting numerical code is demonstrated by using the Schwarzschild black
hole as a test-bed. Its evolution can be followed up to times greater than one
hundred black hole masses.Comment: 11 pages, 4 figures; figure correcte
Towards a Singularity-Proof Scheme in Numerical Relativity
Progress in numerical relativity has been hindered for 30 years because of
the difficulties of avoiding spacetime singularities in numerical evolution. We
propose a scheme which excises a region inside an apparent horizon containing
the singularity. Two major ingredients of the scheme are the use of a
horizon-locking coordinate and a finite differencing which respects the causal
structure of the spacetime. Encouraging results of the scheme in the spherical
collapse case are given.Comment: 9 page
Collisions of boosted black holes: perturbation theory prediction of gravitational radiation
We consider general relativistic Cauchy data representing two nonspinning,
equal-mass black holes boosted toward each other. When the black holes are
close enough to each other and their momentum is sufficiently high, an
encompassing apparent horizon is present so the system can be viewed as a
single, perturbed black hole. We employ gauge-invariant perturbation theory,
and integrate the Zerilli equation to analyze these time-asymmetric data sets
and compute gravitational wave forms and emitted energies. When coupled with a
simple Newtonian analysis of the infall trajectory, we find striking agreement
between the perturbation calculation of emitted energies and the results of
fully general relativistic numerical simulations of time-symmetric initial
data.Comment: 5 pages (RevTex 3.0 with 3 uuencoded figures), CRSR-107
Adaptive mesh refinement approach to construction of initial data for black hole collisions
The initial data for black hole collisions is constructed using a
conformal-imaging approach and a new adaptive mesh refinement technique, a
fully threaded tree (FTT). We developed a second-order accurate approach to the
solution of the constraint equations on a non-uniformly refined high resolution
Cartesian mesh including second-order accurate treatment of boundary conditions
at the black hole throats. Results of test computations show convergence of the
solution as the numerical resolution is increased. FTT-based mesh refinement
reduces the required memory and computer time by several orders of magnitude
compared to a uniform grid. This opens up the possibility of using Cartesian
meshes for very high resolution simulations of black hole collisions.Comment: 13 pages, 11 figure
Cloud-Chamber Observations of Some Unusual Neutral V Particles Having Light Secondaries
From six cloud-chamber photographs of unusual V0 decay events, the following conclusions are drawn: (1) there is a neutral V particle that decays into two particles lighter than κ mesons with a Q value too small to be consistent with a θ0(π, π, 214 Mev) particle; (2) some of these events cannot be explained in terms of the decay of a τ0(π0, π-, π+, Q∼80 Mev) particle; (3) these events can be explained by any one of a number of three-body decay schemes, but two different types of V particles must be postulated if two-body decays are assumed
Evolution of magnetized, differentially rotating neutron stars: Simulations in full general relativity
We study the effects of magnetic fields on the evolution of differentially
rotating neutron stars, which can form in stellar core collapse or binary
neutron star coalescence. Magnetic braking and the magnetorotational
instability (MRI) both redistribute angular momentum; the outcome of the
evolution depends on the star's mass and spin. Simulations are carried out in
axisymmetry using our recently developed codes which integrate the coupled
Einstein-Maxwell-MHD equations. For initial data, we consider three categories
of differentially rotating, equilibrium configurations, which we label normal,
hypermassive and ultraspinning. Hypermassive stars have rest masses exceeding
the mass limit for uniform rotation. Ultraspinning stars are not hypermassive,
but have angular momentum exceeding the maximum for uniform rotation at the
same rest mass. We show that a normal star will evolve to a uniformly rotating
equilibrium configuration. An ultraspinning star evolves to an equilibrium
state consisting of a nearly uniformly rotating central core, surrounded by a
differentially rotating torus with constant angular velocity along magnetic
field lines, so that differential rotation ceases to wind the magnetic field.
In addition, the final state is stable against the MRI, although it has
differential rotation. For a hypermassive neutron star, the MHD-driven angular
momentum transport leads to catastrophic collapse of the core. The resulting
rotating black hole is surrounded by a hot, massive, magnetized torus
undergoing quasistationary accretion, and a magnetic field collimated along the
spin axis--a promising candidate for the central engine of a short gamma-ray
burst. (Abridged)Comment: 27 pages, 30 figure
Thermal Hair of Quantum Black Hole
We investigate the possibility of statistical explanation of the black hole
entropy by counting quasi-bounded modes of thermal fluctuation in two
dimensional black hole spacetime. The black hole concerned is quantum in the
sense that it is in thermal equilibrium with its Hawking radiation. It is shown
that the fluctuation around such a black hole obeys a wave equation with a
potential whose peaks are located near the black hole and which is caused by
quantum effect. We can construct models in which the potential in the above
sense has several positive peaks and there are quai-bounded modes confined
between these peaks. This suggests that these modes contribute to the black
hole entropy. However it is shown that the entropy associated with these modes
dose not obey the ordinary area law. Therefore we can call these modes as an
additional thermal hair of the quantum black hole.Comment: LaTeX, 12 pages, 14 postscript figures, submitted to Phys. Rev.
Can a combination of the conformal thin-sandwich and puncture methods yield binary black hole solutions in quasi-equilibrium?
We consider combining two important methods for constructing
quasi-equilibrium initial data for binary black holes: the conformal
thin-sandwich formalism and the puncture method. The former seeks to enforce
stationarity in the conformal three-metric and the latter attempts to avoid
internal boundaries, like minimal surfaces or apparent horizons. We show that
these two methods make partially conflicting requirements on the boundary
conditions that determine the time slices. In particular, it does not seem
possible to construct slices that are quasi-stationary and avoid physical
singularities and simultaneously are connected by an everywhere positive lapse
function, a condition which must obtain if internal boundaries are to be
avoided. Some relaxation of these conflicting requirements may yield a soluble
system, but some of the advantages that were sought in combining these
approaches will be lost.Comment: 8 pages, LaTeX2e, 2 postscript figure
Magnetohydrodynamics in full general relativity: Formulation and tests
A new implementation for magnetohydrodynamics (MHD) simulations in full
general relativity (involving dynamical spacetimes) is presented. In our
implementation, Einstein's evolution equations are evolved by a BSSN formalism,
MHD equations by a high-resolution central scheme, and induction equation by a
constraint transport method. We perform numerical simulations for standard test
problems in relativistic MHD, including special relativistic magnetized shocks,
general relativistic magnetized Bondi flow in stationary spacetime, and a
longterm evolution for self-gravitating system composed of a neutron star and a
magnetized disk in full general relativity. In the final test, we illustrate
that our implementation can follow winding-up of the magnetic field lines of
magnetized and differentially rotating accretion disks around a compact object
until saturation, after which magnetically driven wind and angular momentum
transport inside the disk turn on.Comment: 28 pages, to be published in Phys. Rev.
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