Publications (15) View all
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Article: Dynamical Bar-Mode Instability in Differentially Rotating Magnetized Neutron Stars
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ABSTRACT: 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 version11/2009; -
Article: Three Dimensional Distorted Black Holes
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ABSTRACT: We present three-dimensional, {\it non-axisymmetric} distorted black hole initial data which generalizes the axisymmetric, distorted, non-rotating [Bernstein93a] and rotating [Brandt94a] single black hole data developed by Bernstein, Brandt, and Seidel. These initial data should be useful for studying the dynamics of fully 3D, distorted black holes, such as those created by the spiraling coalescence of two black holes. We describe the mathematical construction of several families of such data sets, and show how to construct numerical solutions. We survey quantities associated with the numerically constructed solutions, such as ADM masses, apparent horizons, measurements of the horizon distortion, and the maximum possible radiation loss ($MRL$).07/2002; -
Article: A Numerical Study of Three-Dimensional Black Hole Spacetimes
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ABSTRACT: We present results from numerical evolutions of vacuum black hole spacetimes in 3D Cartesian coordinates. We first studied the Schwarzschild spacetime, comparing extensively with 1D studies. We show that although accurate 3D evolutions are possible, there are a number of difficulties in evolving 3D black holes, for which we suggest approaches to overcome. With current limits on computer memory sizes, we show that with certain slicing conditions, the black hole can be evolved to about t= 50M, where M is the black hole mass. We also present the first 3D evolutions of colliding black holes, with evolutions of the axisymmetric Misner two-black hole initial data sets. Here we demonstrate that the techniques we developed for the Schwarzschild case carry over to other spacetimes. We also demonstrate the feasibility of extracting gravitational wave signals during 3D evolutions. We present new, fully 3D distorted black hole initial data sets, extending Bernstein's axisymmetric data sets in a straightforward way. Metric functions and waveforms from evolutions of these data sets in the axisymmetric limit are shown to agree with 2D calculations. For evolutions of the non-axisymmetric sets, which are the first truly 3D black hole data sets to be evolved, all non-trivial wave modes through /ell=4 are presented. Finally, we point the way towards studying the evolution of these data sets with perturbation theory.11/1998; -
Article: Black Hole Spectroscopy: Determining Waveforms from 3D Excited Black Holes
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ABSTRACT: We present the first results for Cauchy nonlinear evolution of 3D, nonaxisymmetric distorted black holes. We focus on the extraction and verification of 3D waveforms determined by numerical relativity. We show that the black hole evolution can be accurately followed through the ringdown period, and comparing with a recently developed perturbative evolution technique, we show that many waveforms in the black hole spectrum of modes, such as l=2 and l=4, including weakly excited nonaxisymmetric modes with m not zero, can be accurately evolved and extracted from the full nonlinear numerical evolution. We also identify new physics contained in higher modes, due to nonlinear effects. The implications for simulations related to gravitational wave astronomy are discussed.07/1998; -
Article: Evolution of Distorted Black Holes: A Perturbative Approach
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ABSTRACT: We consider a series of distorted black hole initial data sets, and develop techniques to evolve them using the linearized equations of motion for the gravitational wave perturbations on a Schwarzschild background. We apply this to 2D and 3D distorted black hole spacetimes. In 2D, waveforms for different modes of the radiation are presented, comparing full nonlinear evolutions for different axisymmetric l-modes with perturbative evolutions. We show how axisymmetric black hole codes solving the full, nonlinear Einstein equations are capable of very accurate evolutions, and also how these techniques aid in studying nonlinear effects. In 3D we show how the initial data for the perturbation equations can be computed, and we compare with analytic solutions given from a perturbative expansion of the initial value problem. In addition to exploring the physics of these distorted black hole data sets, in particular allowing an exploration of linear, nonlinear, and mode mixing effects, this approach provides an important testbed for any fully nonlinear numerical code designed to evolve black hole spacetimes in 2D or 3D.07/1998;
