  Compact object mergers eject neutron-rich matter in a number of ways: by the
dynamical ejection mediated by gravitational torques, as neutrino-driven winds
and probably also a good fraction of the resulting accretion disc finally
becomes unbound by a combination of viscous and nuclear processes. If compact
binary mergers produce indeed gamma-ray bursts there should also be an
interaction region where an ultra-relativistic outflow interacts with the
neutrino-driven wind and produces moderately relativistic ejecta. Each type of
ejecta has different physical properties and therefore plays a different role
for nucleosynthesis and for the electromagnetic transients that go along with
compact object encounters. Here we focus on the dynamic ejecta and present
results for over 30 hydrodynamical simulations of both gravitational
wave-driven mergers and parabolic encounters as they may occur in globular
clusters. We find that mergers eject $\sim 1$% of a solar mass of extremely
neutron-rich material. The exact amount as well as the ejection velocity
depends on the involved masses with asymmetric systems ejecting more material
at higher velocities. This material undergoes a robust r-process and both
ejecta amount and abundance pattern are consistent with neutron star mergers
being a major source of the "heavy" ($A>130$) r-process isotopes. Parabolic
collisions, especially those between neutron stars and black holes, eject
substantially larger amounts of mass and therefore cannot occur frequently
without overproducing galactic r-process matter. We also discuss the
electromagnetic transients that are powered by radioactive decays within the
ejecta ("Macronovae"), and the radio flares that emerge when the ejecta
dissipate their large kinetic energies in the ambient medium.

High Energy Astrophysical Phenomena