Gravitational radiation during coalescence of neutron stars

Abstract

The coalescence of components of a binary star with equal masses (M1 = M2 = M⊙) and moving in circular orbits is considered. The equation of state for degenerate neutrons is used, leading to the equation of state for an ideal gas. The initial model has zero temperature, corresponding to a polytrope with n = 1.5. To reduce the required computational time, the initial close binary is constructed using the self-consistent field method. The computations use Newtonian gas dynamics, but the back reaction of the gravitational radiation is taken into account in a PN2.5 post-Newton approximation, obtained using ADM formalism. This makes it possible to apply previous experienceof constructing high-order Godunov-type difference schemes, which are suitable for end-to-end calculations of discontinuous solutions of the gas-dynamics equations on a fixed Eulerian grid. The Poisson equations were solved using an original spherical-function expansion method. The 3D computations yielded the parameters of the gravitational signal. Near the radiation maximum, the strain amplitude is rh ∼ 4 × 104 cm, the power maximum is 4 × 1054 erg/s, and the typical radiation frequency is ≳1 kHz. The energy carried away by gravitational waves is ≳1052 erg. These parameters are of interest, since they form an inherent part of a rotational mechanism for the supernova explosion. They are also of interest for the planning of gravitational-wave detection experiments.