COLLIDING NEUTRON-STARS - GRAVITATIONAL-WAVES, NEUTRINO EMISSION, ANDGAMMA-RAY BURSTS

Three-dimensional hydrodynamical simulations are presented for the dir ect head-on or off-center collision of two neutron stars, employing a basically Newtonian PPM code but including the emission of gravitation al waves and their back-reaction on the hydrodynamical flow. A physica l nuclear equation of state is used that allows us to follow the therm odynamical evolution of the stellar matter and to compute the emission of neutrinos. Predicted gravitational wave signals, luminosities and waveforms, are presented. The models are evaluated for their implicati ons for gamma-ray burst scenarios. We find an extremely luminous outbu rst of neutrinos with a peak luminosity of more than 4 . 10(54) erg/s for several milliseconds. This leads to an efficiency of about 1% for the annihilation of neutrinos with antineutrinos, corresponding to an average energy deposition rate of more than 10(52) erg/s and a total e nergy of about 10(50) erg deposited in electron-positron pairs around the collision site within 10 ms. Although these numbers seem very favo rable for gamma-ray burst scenarios, the pollution of the ef pair-plas ma cloud with nearly 10(-1) M. of dynamically ejected baryons is 5 ord ers of magnitude too large. Therefore the formation of a relativistica lly expanding fireball that leads to a gamma-ray burst powered by neut rino emission from colliding neutron stars is definitely ruled out.