A Way to 3D Numerical Relativity --- Coalescing Binary Neutron Stars ---

One of the most promising sources of gravitational radiation is coalescence of binary neutron stars or black holes. In order to study gravitational radiation at the merging phase of coalescing binary neutron stars which is called the last three-milliseconds, full general relativistic simulations are required. Since coalescence of binary stars is a completely non-axisymmetric and 3 dimensional (in space) event, which needs great powers of computers, we have to develop a method of 3D numerical relativity using a vector-parallel supercomputer. As a first step of this final goal, we started simulations using post-Newtonian hydrodynamics including radiation reaction of gravitational waves from 1989. They gave a lot of perspectives on coalescing events and gravitational radiation from them. Next we started to attack 3D, fully relativistic simulations. First, basic equations on the (3+1)-formalism of the Einstein equations are shown. As for gauge conditions, we use conformal time slicing and psuedo minimal distortion condtions at present. For these conditions as well as to solve initial value equations, we should solve some elliptic partial differential equations. It consumes the greatest part of CPU time. We show recent results of test simulations on coalescing binary neutron stars.