Neutron Star and Black Hole Binaries in the Galaxy

We present a statistical analysis of the number and birthrate of double neutron star (NS-NS) binaries. We estimate that there are ∼10 4.5 z 0 such systems in the Galaxy, with a birthrate ∼10 −5 z 0 /yr, where z 0 (kpc) is their scale height; we expect z 0 ∼ few kpc. We find that mergers of NS-NS binaries through gravitational radiation losses should be occurring roughly once a year in galaxies within 200/h Mpc. Also, we estimate that one out of ∼10 2 /z 0 massive stars in close binaries ends up in a NS-NS system