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Session 38 - Modeling & Numerical Methods.
Display session, Wednesday, June 11
South Main Hall,
Neutron star mergers (NSM) are considered excellent astrophysical laboratories for studies in gravitational wave astronomy, nuclear astrophysics and relativistic astrophysics in dynamic spacetimes. The waveforms from these mergers are expected to be observed by gravitational wave detectors coming on-line in the next decade. Post-Newtonian (PN) methods (Lincoln amp; Will 1990), can accurately describe the evolution of the system when the separation between stars is much larger than the stellar radii. However, tidal effects in the last several orbits are likely to be significant requiring a full hydrodynamic evolution of the system. We evolve the Euler equations using a modification of the ZEUS-2D algorithm (Stone amp; Norman 1992). We have conducted convergence studies to delineate how spatial and temporal resolution affect the conservation of angular momentum and energy in these models. Our results establish what spatial and temporal resolution is necessary to correctly model the global dynamics of coalescence. We will describe the technical difficulties of modeling this problem including the limitations of resolution and the time centering of the elliptic solve. We have included radiation reaction (2.5PN) effects and contrast the role of tidal instabilities (Rasio amp; Shapiro 1994) and gravitational radiation in the coalescence phase. Furthermore, we discuss the h_+ and h_\times gravitational wave signals and luminosity from the merger. We comment on the possibility of NSM as the site of the astrophysical \i r-process. Our numerical models consider both polytropic and more realistic equations of state describing neutron stars. We consider a variety of initial conditions involving spins and masses of the neutron stars. We compare our results to those of other groups who have performed similar calculations.
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