  We have performed detailed population synthesis on a large number (20
million) of binary systems in order to investigate the properties of massive
double degenerate binaries. We have included new important results in our input
physics in order to obtain more reliable estimates of the merging timescales
and relative formation rates. These improvements include refined treatment of
the binding energy in a common envelope, helium star evolution and reduced
kicks imparted to newborn black holes. The discovery and observations of GRB
afterglows and the identification of host galaxies have allowed comparisons of
theoretical distributions of merger sites with the observed distribution of
afterglow positions relative to host galaxies. To help investigate the physical
nature of short- and long-duration GRBs, we compute the distances of merging
neutron stars (NS) and/or black holes (BH) from the centers of their host
galaxies, as predicted by their formation scenario combined with motion in
galactic potentials. Furthermore, we estimate the formation rate and merging
rate of these massive double degenerate binaries. The latter is very important
for the prospects of detecting gravitational waves with LIGO/VIRGO. We find
that the expected detection rate for LIGO II is ~850 per year for galactic
field sources and that this rate is completely dominated by merging BHBH
binaries. Even LIGO I may detect such an event (~0.25 per year). Our preferred
model estimate the Galactic field NSNS merger rate to be ~1.5*10^(-6) per year.
For BHBH systems this model predicts a merger rate of ~9.7*10^{-6} per year.
Our studies also reveal an accumulating numerous population of very wide orbit
BHBH systems which never merge (t >> t_Hubble).
