Bulletin of the American Physical Society
APS April Meeting 2014
Volume 59, Number 5
Saturday–Tuesday, April 5–8, 2014; Savannah, Georgia
Session R15: Numerical Relativity with Matter: Methods and Simulations II |
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Chair: William East, Princeton University Room: 103 |
Monday, April 7, 2014 10:45AM - 10:57AM |
R15.00001: Magnetized Neutron Stars With Realistic Equations of State and Neutrino Cooling Steven Liebling, David Neilsen, Matthew Anderson, Luis Lehner, Carlos Palenzuela We incorporate realistic, tabulated equations of state into fully relativistic simulations of magnetized neutron stars along with a neutrino leakage scheme which accounts for cooling via neutrino emission. Both these improvements utilize open-source code (GR1D) and tables from http://stellarcollapse.org. Our implementation makes use of a novel method for the calculation of the optical depth which simplifies its use with distributed adaptive mesh refinement, such as we have. We present various tests and preliminary results both from single stars and from binary mergers with and without initial magnetization. [Preview Abstract] |
Monday, April 7, 2014 10:57AM - 11:09AM |
R15.00002: Electromagnetic Counterparts from Tilted Magnetized Binary Neutron-Stars Mergers Marcelo Ponce, Carlos Palenzuela, Patrick M. Motl, Matthew Anderson, Eric W. Hirschmann, Luis Lehner, Steven L. Liebling, David Neilsen Recent studies have demonstrated that the interaction of magnetospheres in binary neutron star systems can radiate strongly electromagnetically [1,2]. We study here a broader set of configurations accounting for tilted/misaligned dipoles in coalescing binaries and analyze the resulting Poynting flux and its correlation to the dynamics. In particular, the misalignment of the dipoles results in a very dynamic system with magnetic reconnections, sheer layers, and current sheets. The electromagnetic radiation displays a distinctive pulsating behaviour tied to the orbital dynamics and stellar dipole orientations and the overall power of this radiation. \\ ~[1] C.~Palenzuela, L.~Lehner, M.~Ponce, S.~L.~Liebling, M.~Anderson, D.~Neilsen and P.~Motl, Phys.\ Rev.\ Lett.\ {\bf 111}, 061105 (2013) \\ ~[2] C.~Palenzuela, L.~Lehner, S.~L.~Liebling, M.~Ponce, M.~Anderson, D.~Neilsen and P.~Motl, Phys.\ Rev.\ D {\bf 88}, 043011 (2013) [Preview Abstract] |
Monday, April 7, 2014 11:09AM - 11:21AM |
R15.00003: Beyond 2nd order in the simulations of binary neutron stars in general relativity David Radice, Luciano Rezzolla, Filippo Galeazzi The inspiral and merger of binary neutron stars (BNSs) is one of the most promising sources of gravitational waves (GWs) for future ground-based laser detectors such as LIGO, Virgo or KAGRA. GWs carry valuable information concerning the binary parameters as well as the equation of state of neutron stars. Extracting such information, however, requires the use of accurate models of GWs that can only be constructed using numerical-relativity simulations. Even though few high-quality BNSs waveforms have been computed in the past few years, substantial difficulties need to be addressed to be able to cover the parameter space of BNSs and produce reliable GWs templates. In this talk I present some recent progress in the modeling of BNSs in numerical relativity. In particular I will show how, with the use of higher-order numerical schemes, we were able to obtain GWs signals showing, for the first time, higher-than-second-order accuracy in the phase and amplitude evolution. Our results are also in excellent agrenment with the predictions of post-Newtonian theory almost up to the contact frequency of the binary. [Preview Abstract] |
Monday, April 7, 2014 11:21AM - 11:33AM |
R15.00004: Magnetar Formation from the Merger of Binary Neutron Stars Bruno Giacomazzo I will discuss the results of recent fully general relativistic magnetohydrodynamic (GRMHD) simulations of binary neutron star (BNS) mergers performed with the Whisky code. I will describe in particular the role of magnetic fields in the post-merger dynamics, their impact on gravitational waves (GWs), and the possible formation of magnetars. The formation of a rapidly spinning magnetar after the merger could in particular generate electromagnetic signals that, if measured together with GWs emitted during the inspiral, could help to constrain the equation of state of NSs. Moreover BNSs are also thought to be behind the central engine of short gamma-ray bursts (SGRBs) and the formation of a magnetar could explain some of the observed SGRBs. While global GRMHD simulations of BNS mergers are currently unable to produce strong magnetic field amplifications during merger, local high-resolution simulations showed that small-scale turbulence can play a very important role in amplifying the magnetic fields. I will show how such small-scale dynamics can be included in global GRMHD BNS simulations via the implementation of a subgrid-scale model and its effect on the formation of magnetars. [Preview Abstract] |
Monday, April 7, 2014 11:33AM - 11:45AM |
R15.00005: Binary neutron stars with realistic spin Wolfgang Tichy, Sebastiano Bernuzzi, Tim Dietrich, Bernd Bruegmann Astrophysical neutron stars are expected to be spinning. We present the first, fully nonlinear general relativistic dynamical evolutions of the last three orbits for constraint satisfying initial data of spinning neutron star binaries, with astrophysically realistic spins aligned and anti-aligned to the orbital angular momentum. The dynamics of the systems are analyzed in terms of gauge-invariant binding energy vs. orbital angular momentum curves. By comparing to a binary black hole configuration we can estimate the different tidal and spin contributions to the binding energy for the first time. First results on the gravitational wave forms are presented. The phase evolution of the gravitational waves during the orbital motion is significantly affected by spin-orbit interactions, leading to delayed or early mergers. Furthermore, a frequency shift in the main emission mode of the hyper massive neutron star is observed. Our results suggest that a detailed modeling of merger waveforms requires the inclusion of spin, even for the moderate magnitudes observed in binary neutron star systems. [Preview Abstract] |
Monday, April 7, 2014 11:45AM - 11:57AM |
R15.00006: Evolutions of eccentric binary neutron stars with improved initial data Nathan Johnson-McDaniel, Niclas Moldenhauer, Charalampos Markakis, Bernd Br{\"u}gmann, Wolfgang Tichy We describe the first evolutions of eccentric binary neutron stars using initial data constructed with a new method that solves the Einstein constraints and Euler equation self-consistently, which previously had only been done in the quasicircular case. We show that these data indeed lead to considerable improvement in the initial spurious oscillation of the neutron stars, compared with the superposed data used in previous evolutions. We also consider the convergence of the constraints, the gravitational wave signal (including the tidally induced oscillations), and the properties of the final remnant and ejecta, again comparing the evolutions of the new data with those of the old, superposed data. [Preview Abstract] |
Monday, April 7, 2014 11:57AM - 12:09PM |
R15.00007: Binary NS simulations using SpEC Roland Haas, Bela Szilagyi, Jeffrey Kaplan, Christian Ott, Jonas Lippuner, Mark Scheel, Kevin Barkett, Curran Muhlberger, Francois Foucart, Matthew Duez NSNS binaries are expected to be one of the major sources of gravitational radiation detectable by Advanced LIGO. Together with neutrinos, gravitational waves are our only means to learn about the processes deep within a merging pair of NS, shedding light on the as yet poorly understood, equation of state governing matter at nuclear densities and beyond. We report on binary neutron star simulations using the Spectral Einstein Code (SpEC) developed by the Caltech-Cornell-CITA-WSU collaboration. We simulate the inspiral through many orbits, follow the post-merger evolution, and compute the full gravitational wave signal. [Preview Abstract] |
Monday, April 7, 2014 12:09PM - 12:21PM |
R15.00008: Exploring the Use of Discontinuous Galerkin Methods for Numerical Relativity Francois Hebert, Lawrence Kidder, Saul Teukolsky With Advanced LIGO expected to start detecting gravitational wave signals in the next several years, it is important that numerical simulations be able to generate the accurate gravitational wave templates used for both detection and parameter estimation. Generating these accurate gravitational wave templates is particularly challenging for black hole-neutron star mergers or binary-neutron star mergers: the algorithms used in the matter evolution, based on the finite volume method, struggle to reach the desired accuracy. We believe that a different type of algorithm, the discontinuous Galerkin method, would significantly increase the simulation accuracy thanks to its spectral convergence properties for smooth solutions and its robust stability properties for shocks. We present here our initial work implementing and testing a discontinuous Galerkin code on simple problems, leading towards the development of a discontinuous Galerkin-based GR hydro code. [Preview Abstract] |
Monday, April 7, 2014 12:21PM - 12:33PM |
R15.00009: Multi-patch methods for magnetohydrodynamic accretion simulations Fatemeh Hossein Nouri Black hole accretion is one of the most important processes in relativistic astrophysics. Numerical simulations must accurately track both disks, polar jets, and near-horizon inflows. However, many standard numerical techniques face challenges evolving some region of the fluid, at least for some range of black hole spin. Cartesian grids with legosphere excision allow outgoing characteristics and are often unstable. Spherical-polar grids suffer extreme Courant time step limitations and coordinate singularities if the poles are evolved. In this talk, we explore two other ways of evolving MHD accretion. One, already in use in numerical relativity for moderate black hole spins, is to remove the black hole interior by a coordinate transformation. The other is to evolve using cubed-sphere multipatches, which allow a horizon-conforming inner boundary without any bad behavior at the poles. We discuss our implementation of this scheme in the SpEC code and report test evolutions of magnetized accretion tori around high-spin black holes. [Preview Abstract] |
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