Massive double compact object mergers: gravitational wave sources and
  r-process-element production sites
  With our galactic evolutionary code that contains a detailed intermediate
mass and massive binary population model, we study the temporal evolution of
the galactic population of double neutron star binaries, mixed systems with a
neutron star and black hole component and double black hole binaries. We
compute the merger rates of these relativistic binaries and we translate them
into LIGO II detection rates. We demonstrate that accounting for the
uncertainties in the relation 'initial mass-final mass' predicted by massive
close binary evolution and due to the possible effect of large stellar wind
mass loss during the luminous blue variable phase of a star with initial mass
larger than 30-40 Mo and during the red supergiant phase of a star with initial
mass smaller than 30-40 Mo when such a star is a binary component, the double
black hole merger rate may be very small, contrary to predictions made by other
groups. Hydrodynamic computations of r-process chemical yields ejected during
the relativistic binary merger process have recently become available. With our
galactic code that includes binaries it is then straightforward to calculate
the temporal galactic evolution of the r-process elements ejected by these
mergers. We conclude that except for the earliest evolutionary phase of the
Galaxy (~the first 100 Myr) double compact star mergers may be the major
production sites of r-process elements and it is probable that the mixed
systems dominate this production over double neutron star binary mergers.
