Bulletin of the American Physical Society
APS April Meeting 2016
Volume 61, Number 6
Saturday–Tuesday, April 16–19, 2016; Salt Lake City, Utah
Session U15: Initial Data and Head-On Collisions in Numerical Relativity |
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Sponsoring Units: GGR Chair: Bernard Kelly, NASA Room: 251C |
Monday, April 18, 2016 3:30PM - 3:42PM |
U15.00001: New Approach for Initial Data of Compact Object Binaries Michael Clark, Pablo Laguna We present a new construction for initial data for simulations of binary systems with neutron stars. This method generalizes the Bowen-York extrinsic curvature for puncture black holes to TOV model stars while still satisfying the momentum constraint. We use this construction to generate binary systems involving neutron stars, using post-Newtonian approximations to compute the necessary momenta for the objects given the mass ratio, separation, and spins. We compare fully evolved simulations using this data to other systems in the literature, for double neutron star binaries and mixed black hole/neutron star binaries, with and without spin. We also analyze the oscillation modes of a single neutron star generated by this data. [Preview Abstract] |
Monday, April 18, 2016 3:42PM - 3:54PM |
U15.00002: Binary Black Hole Initial Data Without Elliptic Equations Jeffrey Winicour, Istvan Racz We describe a radically new method for solving the constraints of Einstein's equations which does not involve elliptic equations. Instead, the constraints are formulated as a symmetric hyperbolic system which can be integrated radially inward from an outer boundary. In this method, the initial metric data for a binary black hole can be freely prescribed, e.g. in a 4-dimensional superimposed Kerr-Schild form for the individual boosted black holes. Two pieces of extrinsic curvature data, which represent the two gravitational degrees of freedom, can also be freely prescribed by superimposing the individual black hole data. The remaining extrinsic curvature data are then determined by the hyperbolic constraint system. Because no puncture or excision boundary conditions are necessary, this approach offers a simple alternative that could provide more physically realistic binary black hole initial data than present methods. Here we present a computational framework for implementing this new method. [Preview Abstract] |
Monday, April 18, 2016 3:54PM - 4:06PM |
U15.00003: A Hyperbolic Solver for Black Hole Initial Data in Numerical Relativity Maria Babiuc Numerical relativity is essential to the efforts of detecting gravitational waves emitted at the inspiral and merger of binary black holes. The first requirement for the generation of reliable gravitational wave templates is an accurate method of constructing initial data (ID). The standard approach is to solve the constraint equations for general relativity by formulating them as an elliptic system. A shortcoming of the ID constructed this way is an initial burst of spurious unphysical radiation (junk radiation). Recently, Racz and Winicour formulated the constraints as a hyperbolic problem, requiring boundary conditions only on a large sphere surrounding the system, where the physical behavior of the gravitational field is well understood. We investigate the applicability of this new approach, by developing a new 4th order numerical code that implements the fully nonlinear constraints equations on a two dimensional stereographic foliation, and evolves them radially inward using a Runge-Kutta integrator. The tensorial quantities are written as spin-weighted fields and the angular derivatives are replaced with ``eth'' operators. We present here results for the simulation of nonlinear perturbations to Schwarzschild ID in Kerr-Schild coordinates. The code shows stability and convergence at both large and small radii. Our long-term goal is to develop this new approach into a numerical scheme for generating ID for binary black holes and to analyze its performance in eliminating the junk radiation. [Preview Abstract] |
Monday, April 18, 2016 4:06PM - 4:18PM |
U15.00004: Highly Spinning Initial Data: Gauges and Accuracy Yosef Zlochower, Ian Ruchlin, James Healy, Carlos Lousto We recently developed a code for solving the 3+1 system of constraints for highly-spinning black-hole binary initial data in the puncture formalism. Here we explore how different choices of gauge for the background metric improve both the efficiency and accuracy of the initial data solver and the subsequent fully nonlinear numerical evolutions of these data. [Preview Abstract] |
Monday, April 18, 2016 4:18PM - 4:30PM |
U15.00005: Computing Binary Black Hole Initial Data in Damped Harmonic Gauge Vijay Varma, Mark Scheel Binary black hole evolution in the Spectral Einstein Code (SpEC) is currently done in the damped harmonic (DH) gauge, which has proven very useful for merger simulations. However, the initial data for the simulation is constructed in a different gauge. Once the evolution starts we need to perform a smooth gauge transformation to the DH gauge, introducing additional gauge dynamics into the evolution. In this work, we construct the initial data in the DH gauge itself, which allows us to avoid the above gauge transformation. This can have added benefits such as possibly reducing junk radiation, making it easier to achieve a desired orbital eccentricity, reducing the runtime of simulations, and being able to start evolution closer to the merger. [Preview Abstract] |
Monday, April 18, 2016 4:30PM - 4:42PM |
U15.00006: Computing Binary Black Hole Initial Data with Discontinuous Galerkin Methods Trevor Vincent, Harald Pfeiffer Discontinuous Galerkin (DG) finite element methods have been used to solve hyperbolic PDEs in relativistic simulations and offer advantages over traditional discretization methods. Comparatively little attention has been given towards using the DG method to solve the elliptic PDEs arising from the Einstein initial data equations. We describe how the DG method can be used to create a parallel, adaptive solver for initial data. We discuss the use of our dG code to compute puncture initial data for binary black holes. [Preview Abstract] |
Monday, April 18, 2016 4:42PM - 4:54PM |
U15.00007: Ultrarelativistic unequal-mass black hole collisions Emanuele Berti, Ulrich Sperhake, Vitor Cardoso, Frans Pretorius We study unequal-mass, high-energy head-on collisions of black holes in four dimensions. We show that the fraction of the center-of-mass energy radiated as gravitational waves becomes independent of mass ratio and approximately equal to 13\% at large energies. We support this conclusion with calculations using black hole perturbation theory and Smarr's zero-frequency limit approximation. These results lend strong support to the conjecture that the detailed structure of the colliding objects is irrelevant at high energies. [Preview Abstract] |
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