The evolution of wide binary stars

Abstract

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