EXPECTED COALESCENCE RATES OF NS-NS BINARIES FOR LASER BEAM INTERFEROMETERS

Abstract

The coalescence rate of two neutron stars (NS) is revisited. To estimate the number of bound NS-NS and the probability of their coalescence in a time scale τ, the galactic star formation history, directly derived from observations, and the evolution of massive stars are considered. The newly established galactic merging rate is (1.7±1.0) × 10-5 yr -1, while the local merging rate, including the contribution of elliptical galaxies, is about a factor of two higher, 3.4 × 10-5 yr -1. Using the present data basis on galaxy distribution in the local universe and the expected sensitivity of the first generation of laser beam interferometers, we estimate that one event should occur every 125 years for LIGO and one event each 148 years for VIRGO. The situation is considerably improved for advanced-LIGO, since we predict that 6 events per year should be detected whereas for a recently proposed VIRGO new configuration, the event rate might increase up to 3 events every two years.