Very Wide Binary Stars as the Primary Source of Stellar Collisions in the Galaxy

TL;DR

This study uses numerical simulations to show that very wide binary stars in the Milky Way are likely the main source of stellar collisions, occurring roughly every 1000-7500 years due to orbital perturbations.

Contribution

It demonstrates that very wide binaries are a potentially dominant, previously underappreciated source of stellar collisions in the galaxy, emphasizing the role of orbital dynamics and tidal effects.

Findings

Stellar collisions in wide binaries occur every 1000-7500 years.

Wide binaries can transform into close binaries due to tidal dissipation.

Collisions produce Li-depleted, rapidly rotating massive stars.

Abstract

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.