  We discuss (3+1) dimensional general relativistic hydrodynamic simulations of
close neutron star binary systems. The relativistic field equations are solved
at each time slice with a spatial 3-metric chosen to be conformally flat.
Against this solution the hydrodynamic variables and gravitational radiation
are allowed to respond. We have studied four physical processes which occur as
the stars approach merger. These include: 1) the relaxation to a hydrodynamic
state of almost no spin; 2) relativistically driven compression, heating, and
neutrino emission; 3) collapse to two black holes; and 4) orbit inspiral
occurring at a lower frequency than previously expected. We give a brief
account of the physical origin of these effects and an explanation of why they
do not appear in models based upon, 1PN hydrodynamics, a weak field multipole
expansion, a tidal analysis, or a rigidly corotating velocity field. The
implication of these results for gravity wave detectors is also discussed.
