The triple evolution dynamical instability: Stellar collisions in the field and the formation of exotic binaries

TL;DR

This paper introduces the triple evolution dynamical instability (TEDI) as a new pathway for stellar collisions and the formation of exotic binaries in the galactic field, showing it occurs more frequently than previously thought.

Contribution

The study presents the TEDI mechanism, demonstrating its significance in stellar collisions and binary formation, which challenges the traditional view that such events are rare outside dense clusters.

Findings

TEDI causes stellar collision rate of ~10^{-4} yr^{-1} in the Milky Way.

Most collisions involve asymptotic giant branch stars, not main sequence stars.

TEDI rate is nearly 30 times higher than collision rate in globular clusters.

Abstract

Physical collisions and close approaches between stars play an important role in the formation of exotic stellar systems. Standard theories suggest that collisions are rare, occurring only via random encounters between stars in dense clusters. We present a different formation pathway, the triple evolution dynamical instability (TEDI), in which mass loss in an evolving triple star system causes orbital instability. The subsequent chaotic orbital evolution of the stars triggers close encounters, collisions, exchanges between the stellar components, and the dynamical formation of eccentric compact binaries (including Sirius like binaries). We demonstrate that the rate of stellar collisions due to the TEDI is approximately 10^{-4} yr^{-1} per Milky-Way Galaxy, which is nearly 30 times higher than the total collision rate due to random encounters in the Galactic globular clusters. Moreover, we find that the dominant type of stellar collisions is qualitatively different; most collisions involve asymptotic giant branch stars, rather than main sequence, or slightly evolved stars, which dominate collisions in globular clusters. The TEDI mechanism should lead us to revise our understanding of collisions and the formation of compact, eccentric binaries in the field.