MERGING NEUTRON-STARS .1. INITIAL RESULTS FOR COALESCENCE OF NONCOROTATING SYSTEMS

We present three-dimensional Newtonian simulations of the coalescence of two neutron stars, using a smoothed particle hydrodynamics (SPH) co de. We begin the simulations with the two stars in a hard, circular bi nary, and have them spiral together as angular momentum is lost throug h gravitational radiation at the rate predicted by modeling the system as two point masses. We model the neutron stars as hard polytropes (g amma = 2.4) of equal mass, and investigate the effect of the initial s pin of the two stars on the coalescence. The process of coalescence, f rom initial contact to the formation of an axially symmetric object, t akes only a few orbital periods. Some of the material from the two neu tron stars is shed, forming a thick disk around the central, coalesced object. The mass of this disk is dependent on the initial neutron sta r spins; higher spin rates result in greater mass loss and thus more m assive disks. For spin rates that are most likely to be applicable to real systems, the central coalesced object has a mass of 2.4 M., which is tantalizingly close to the maximum mass allowed by any neutron sta r equation of state for an object that is supported in part by rotatio n. Using a realistic nuclear equation of state, we estimate the temper ature of the material after the coalescence. We find that the central object is at a temperature of - 10 MeV, while the disk is heated by sh ocks to a temperature of 2-4 MeV.