Double Neutron Star Binaries: Implications for LIGO

Double neutrons are especially important because they give most accurate informations on the masses of neutron stars. Observations on double neutron stars show that all masses of the neutron stars are below 1.5$\msun$. Furthermore, two neutron stars in a given double pulsar are nearly equal in mass. With hypercritical accretion, we found that the probability of having companion mass $>1.5\msun$ is larger than 90%, while there is no observations on such systems. We believe that those companions with masses higher than $1.5\msun$ went into black holes, which is consistent with our preferred maximum neutron star mass $M_{NS}^{max} \approx 1.5\msun$ due to the kaon condensation. In this work, we point out that the black-hole neutron star binaries are 10 times more dominant than double neutron star binaries. As a result, black-hole, neutron star binaries can increase the LIGO detection rate by a factor 20.