466 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
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
New Coordinate Systems for Axisymmetric Black Hole Collisions
We describe a numerical grid generating procedure to construct new classes of
orthogonal coordinate systems that are specially adapted to binary black hole
spacetimes. The new coordinates offer an alternative approach to the
conventional \v{C}ade\v{z} coordinates, in addition to providing a potentially
more stable and flexible platform to extend previous calculations of binary
black hole collisions.Comment: 3 pages, 5 postscript figures, LaTeX, uses mprocl.sty (available at
http://shemesh.fiz.huji.ac.il/MG8/submission.html) To appear in the
proceedings of the Marcel Grossmann 8 (Jerusalem, 1997
A Connection Approach to Numerical Relativity
We discuss a general formalism for numerically evolving initial data in
general relativity in which the (complex) Ashtekar connection and the
Newman-Penrose scalars are taken as the dynamical variables. In the generic
case three gauge constraints and twelve reality conditions must be solved. The
analysis is applied to a Petrov type \{1111\} planar spacetime where we find a
spatially constant volume element to be an appropriate coordinate gauge choice.Comment: 17 pages, LaTe
Event Horizons in Numerical Relativity I: Methods and Tests
This is the first paper in a series on event horizons in numerical
relativity. In this paper we present methods for obtaining the location of an
event horizon in a numerically generated spacetime. The location of an event
horizon is determined based on two key ideas: (1) integrating backward in time,
and (2) integrating the whole horizon surface. The accuracy and efficiency of
the methods are examined with various sample spacetimes, including both
analytic (Schwarzschild and Kerr) and numerically generated black holes. The
numerically evolved spacetimes contain highly distorted black holes, rotating
black holes, and colliding black holes. In all cases studied, our methods can
find event horizons to within a very small fraction of a grid zone.Comment: 22 pages, LaTeX with RevTeX 3.0 macros, 20 uuencoded gz-compressed
postscript figures. Also available at http://jean-luc.ncsa.uiuc.edu/Papers/
Submitted to Physical Review
Event Horizons in Numerical Relativity II: Analyzing the Horizon
We present techniques and methods for analyzing the dynamics of event
horizons in numerically constructed spacetimes. There are three classes of
analytical tools we have investigated. The first class consists of proper
geometrical measures of the horizon which allow us comparison with perturbation
theory and powerful global theorems. The second class involves the location and
study of horizon generators. The third class includes the induced horizon
2-metric in the generator comoving coordinates and a set of membrane-paradigm
like quantities. Applications to several distorted, rotating, and colliding
black hole spacetimes are provided as examples of these techniques.Comment: 23 double column pages including 28 figures. Higher quality figures
(big size!) available upon request (jmasso OR [email protected]
Adaptive mesh and geodesically sliced Schwarzschild spacetime in 3+1 dimensions
We present first results obtained with a 3+1 dimensional adaptive mesh code
in numerical general relativity. The adaptive mesh is used in conjunction with
a standard ADM code for the evolution of a dynamically sliced Schwarzschild
spacetime (geodesic slicing). We argue that adaptive mesh is particularly
natural in the context of general relativity, where apart from adaptive mesh
refinement for numerical efficiency one may want to use the built in
flexibility to do numerical relativity on coordinate patches.Comment: 21 pages, LaTeX, 7 figures included with eps
The Evolution of Distorted Rotating Black Holes III: Initial Data
In this paper we study a new family of black hole initial data sets
corresponding to distorted ``Kerr'' black holes with moderate rotation
parameters, and distorted Schwarzschild black holes with even- and odd-parity
radiation. These data sets build on the earlier rotating black holes of Bowen
and York and the distorted Brill wave plus black hole data sets. We describe
the construction of this large family of rotating black holes. We present a
systematic study of important properties of these data sets, such as the size
and shape of their apparent horizons, and the maximum amount of radiation that
can leave the system during evolution. These data sets should be a very useful
starting point for studying the evolution of highly dynamical black holes and
can easily be extended to 3D.Comment: 16 page
The Head-On Collision of Two Equal Mass Black Holes Peter Anninos
We study the head-on collision of two equal mass, nonrotating black holes.
Various initial configurations are investigated, including holes which are
initially surrounded by a common apparent horizon to holes that are separated
by about , where is the mass of a single black hole. We have extracted
both and gravitational waveforms resulting from the
collision. The normal modes of the final black hole dominate the spectrum in
all cases studied. The total energy radiated is computed using several
independent methods, and is typically less than . We also discuss an
analytic approach to estimate the total gravitational radiation emitted in the
collision by generalizing point particle dynamics to account for the finite
size and internal dynamics of the two black holes. The effects of the tidal
deformations of the horizons are analysed using the membrane paradigm of black
holes. We find excellent agreement between the numerical results and the
analytic estimates.Comment: 33 pages, NCSA 94-048, WUGRAV-94-
Finding Apparent Horizons in Dynamic 3D Numerical Spacetimes
We have developed a general method for finding apparent horizons in 3D
numerical relativity. Instead of solving for the partial differential equation
describing the location of the apparent horizons, we expand the closed 2D
surfaces in terms of symmetric trace--free tensors and solve for the expansion
coefficients using a minimization procedure. Our method is applied to a number
of different spacetimes, including numerically constructed spacetimes
containing highly distorted axisymmetric black holes in spherical coordinates,
and 3D rotating, and colliding black holes in Cartesian coordinates.Comment: 19 pages, 13 figures, LaTex, to appear in Phys. Rev. D. Minor changes
mad
- …