The Evolution of Wide Binary Stars
  We study the orbital evolution of wide binary stars in the solar neighborhood
due to gravitational perturbations from passing stars. We include the effects
of the Galactic tidal field and continue to follow the stars after they become
unbound. For a wide variety of initial semi-major axes and formation times, we
find that the number density (stars per unit logarithmic interval in projected
separation) exhibits a minimum at a few times the Jacobi radius r_J, which
equals 1.7 pc for a binary of solar-mass stars. The density peak interior to
this minimum arises from the primordial distribution of bound binaries, and the
exterior density, which peaks at \sim 100--300 pc separation, arises from
formerly bound binaries that are slowly drifting apart. The exterior peak gives
rise to a significant long-range correlation in the positions and velocities of
disk stars that should be detectable in large astrometric surveys such as GAIA
that can measure accurate three-dimensional distances and velocities.
