Very Wide Binary Stars as the Primary Source of Stellar Collisions in
  the Galaxy
  We present numerical simulations modeling the orbital evolution of very wide
binaries, pairs of stars separated by over ~1000 AU. Due to perturbations from
other passing stars and the Milky Way's tide, the orbits of very wide binary
stars occasionally become extremely eccentric, which forces close encounters
between the companion stars (Kaib et al. 2013). We show that this process
causes a stellar collision between very wide binary companion stars once every
1000-7500 years on average in the Milky Way. One of the main uncertainties in
this collision rate is the amount of energy dissipated by dynamic tides during
close (but not collisional) periastron passages. This dissipation presents a
dynamical barrier to stellar collisions and can instead transform very wide
binaries into close or contact binaries. However, for any plausible tidal
dissipation model, very wide binary stars are an unrealized, and potentially
the dominant, source of stellar collisions in our Galaxy. Such collisions
should occur throughout the thin disk of the Milky Way. Stellar collisions
within very wide binaries should yield a small population of single,
Li-depleted, rapidly rotating massive stars.
