Motivation EM Counterparts Extreme Matter Single Star Binary NS Conclusions Modeling Compact Object Binaries (very briefly) Compact Objects: neutron stars (NSs) or black holes (BHs) Binaries: tend to only consider last n orbits before coalescence because of compute time tend to assume circularized orbits (eccentricity tends to get radiated) Lots of numerical software involved: Many scales: AMR Lots of fields and memory: MPI, etc GW wave extraction methods If NSs: HRSC methods EOS: polytropic, perfect fluid (adiabatic index Γ), realistic EOS possibly MHD or resistive MHD or force-free divergence cleaning or constrained transport If BHs: possibly excision Steven L. Liebling Modeling EM and GW from Neutron Stars 1 / 14
Motivation EM Counterparts Extreme Matter Single Star Binary NS Conclusions A couple viewpoints 10 years ago, numerical relativists didn’t ask so much about astrophysics, signals, correlations to data, etc Numerical relativists and astrophysicists are converging....coming from full GR and adding stuff or coming from Newtonian (and a bit post-) and adding GR (Cowling, conformal, ....full GR) Steven L. Liebling Modeling EM and GW from Neutron Stars 2 / 14
Motivation EM Counterparts Extreme Matter Single Star Binary NS Conclusions EM Counterparts Many sources expected to be both EM and GW loud Example from morning: SGRBs from merging BNS or BHNS BHNS mergers...significant remnant mass w/ prograde BH spin BHNS mergers...magnetic field not apparently important (caveats) Rezzolla, et al model BNS merger w/ MHD and find collimated magnetic field Galactic center (ie. low frequency regime): Palenzuela, et al model BHBH w/ force-free...dual-collimated emissions pre-merger (mostly relevant for SMBH galactic BHs) Scott Noble and others doing interesting work with galactic BBH mergers inside fluid Georgia Tech...BBH merger in big ball of gas or a disk Steven L. Liebling Modeling EM and GW from Neutron Stars 3 / 14
Motivation EM Counterparts Extreme Matter Single Star Binary NS Conclusions EM Counterparts Open questions: Can BNS models provide an EM precursor? In general, will EM telescopes identify potential GW sources? Instead, will GW observatories identify potential EM targets? What’s the appropriate EM environment outside COBs and how do we model it? Early stages of magnetic field...could use higher resolution for instabilities (Kelvin-Helmholtz, Tayler, MRI, etc) Steven L. Liebling Modeling EM and GW from Neutron Stars 4 / 14
Motivation EM Counterparts Extreme Matter Single Star Binary NS Conclusions Extreme Matter EOS Recent Work: Friedman, et al modeling BNS with different EOS Shibata, et al modeling BNS using realistic EOSs: Shen and hyperon EOSs Janka, et al 1204.1888 38 different EOS! for BNS ringdown Open questions: Will GW signal differentiate among various EOSs? Answer: pre-merger...doubtful; post-merger BNS: possibly Magnetic field: Beyond EM counterparts, magnetic field affects dynamics...buoyancy, magnetic tension and pressure, etc Open questions: Will GW signal indicate magnetic field strength or configuration? Directly? Steven L. Liebling Modeling EM and GW from Neutron Stars 5 / 14
Motivation EM Counterparts Extreme Matter Single Star Binary NS Conclusions Extreme Matter Microphysics (Neutrino treatments, etc) Becomes relevant at merger when stars heat up Recent Work: Janka, and others Shibata, Sakaguchi, et al with neutrino leakage scheme Open questions: What are the effects of neutrinos for the dynamics and GW production? Is leakage sufficient for the relevant timescales of COB mergers? Steven L. Liebling Modeling EM and GW from Neutron Stars 6 / 14
Motivation EM Counterparts Extreme Matter Single Star Binary NS Conclusions Tests of the Hybridized Force Free [Lehner,Palenzuela,SLL,Thompson,Hanna,arxiv->1112.2622] Single Stable Star: monopole magnetic field stationary solution dipole: aligned rotator of Spitkovsky with Y-point Steven L. Liebling Modeling EM and GW from Neutron Stars 7 / 14
Motivation EM Counterparts Extreme Matter Single Star Binary NS Conclusions Nonrotating Stellar Collapse [Lehner,Palenzuela,SLL,Thompson,Hanna,arxiv->1112.2622] Can match to Force-Free (FF) or Electrovacuum (EV) Compare to Baumgarte & Shapiro ’02 (EV) [astro-ph/0211339] EV radiates (flux radiates) more than FF (flux falls into BH) ...expect the opposite for rotating case Steven L. Liebling Modeling EM and GW from Neutron Stars 8 / 14
Motivation EM Counterparts Extreme Matter Single Star Binary NS Conclusions Rotating Stellar Collapse [Lehner,Palenzuela,SLL,Thompson,Hanna,arxiv->1112.2622] Can match to Force-Free (FF) or Electrovacuum (EV) FF radiates a lot...10 49 ergs or 10 52 erg / s for | B | = 10 15 gauss 1.4 1.2 ev total radiated energy ff 1 0.8 0.6 0.4 0.2 0 -0.4 -0.2 0 0.2 0.4 time (ms) Steven L. Liebling Modeling EM and GW from Neutron Stars 9 / 14
Motivation EM Counterparts Extreme Matter Single Star Binary NS Conclusions Expectations for BH-NS Stellar magnetic field will presumably thread the black hole Generalized BZ-effect will generate Poynting flux, etc McWilliams-Levin argue for plasma current driven back onto NS stellar surface See Marcelo Ponce’s poster: Session K1 Poster Session II 2pm today Grand Hall West From: [McWilliams,Levin, arxiv->1101.1969] Steven L. Liebling Modeling EM and GW from Neutron Stars 10 / 14
Motivation EM Counterparts Extreme Matter Single Star Binary NS Conclusions Expectations for NS-NS Each star (1 . 62 M ⊙ ) moves through field sourced by other star Experience w/ BH-BH system suggests possible similar robust BZ effect L ∝ R 2 B 2 v 2 GRB Precursor from Magnetospheric Interactions? [Hansen,Lyutikov,MNRAS 2001] Aligned Dipoles Anti-aligned Steven L. Liebling Modeling EM and GW from Neutron Stars 11 / 14
Motivation EM Counterparts Extreme Matter Single Star Binary NS Conclusions Electromagnetic Energy vs. Time In the magnetosphere Inside the stars Steven L. Liebling Modeling EM and GW from Neutron Stars 12 / 14
Motivation EM Counterparts Extreme Matter Single Star Binary NS Conclusions Convergence Radiated Energy Movies: anti-aligned aligned Steven L. Liebling Modeling EM and GW from Neutron Stars 13 / 14
Motivation EM Counterparts Extreme Matter Single Star Binary NS Conclusions Conclusions Single NS: stable: consistent results...collimated emission Non-rotating collapse: Very different results: EV and FF: EV: electric field grows and dominates magnetic in places; allows for effective reconnection at speed of light FF: most EM energy falls into BH; Alfv´ en waves carry small amount Rotating collapse: Implications for binary NS merger and core-collapse scenarios, esp. w/r/t GRBs FF allows for fast reconnection, flux vanishes in ≈ 1 ms Presence of even small amounts of conducting matter important NS Binaries: on-going work Possible sGRB precursor Steven L. Liebling Modeling EM and GW from Neutron Stars 14 / 14
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