Numerical Aspects of Simulations of Merging Neutron Stars

Abstract

In order to simulate the merging of two neutron stars with the aim to compute neutrino and gravitational-wave emission, the three-dimensional Newtonian equations of hydrodynamics are integrated by the ’Piecewise Parabolic Method’. We take into account the effects of the emission of gravitational waves and the corresponding backreaction on the hydrodynamics. The properties of neutron star matter are described by the equation of state of Lattimer and Swesty (1991). Energy loss and changes of the electron abundance due to the emission of neutrinos are taken into account by an elaborate “neutrino leakage scheme”, which is based on a careful evaluation of the lepton number and energy source terms of all neutrino and antineutrino flavors. The results of various models with different parameters such as neutron star masses, mass ratios and impact parameters, shed light on the accessable physical conditions during the merger, on the conversion of energy into neutrino emission, on the timescales of mass accretion by black hole assumed to be formed after the merging, and on the amount of matter dynamically ejected during the merging.