Very Wide Binary Stars as the Primary Source of Stellar Collisions in the Galaxy
Résumé
Although rare in the Milky Way, star-star collisions are predicted to occur within the dense cores of globular clusters, in evolving triple star systems, and possibly very near the Galactic center. It has recently been shown that very wide binary star systems (binary stars separated by at least 1000 AU, where 1 AU is the Earth-Sun distance) can have their stellar orbits driven to very eccentric states by other passing field stars and the Galactic tide, forcing close passages between companion stars. Here we report numerical simulations demonstrating that this process is a major but unrealized source of stellar collisions. Occasionally, the eccentricities of very wide binaries become so extreme that their periastron (distance of closest approach, or q) falls below the combined radii of the companion stars, and they collide during periastron passage. Tidal interactions between the companion stars prevent some collisions by shrinking the binary orbit thereby making it less susceptible to galactic perturbations. Nonetheless, this mechanism produces a stellar collision every ~2500 years in the Galaxy, making very wide binaries the dominant source of collisions in the Milky Way. These collisions should yield a small population of single, Li-depleted, rapidly rotating massive stars.