  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.
