Chaotic dynamics of wide triples induced by galactic tides: a novel channel for producing compact binaries, mergers, and collisions

TL;DR

This paper investigates how galactic tides induce chaotic dynamics in wide triple star systems, leading to high eccentricities, mergers, and collisions, which could explain various stellar phenomena and transient events.

Contribution

It introduces a novel secular evolution code and population-synthesis study to quantify the impact of galactic tides on wide triples, revealing a significant rate of stellar mergers and collisions.

Findings

Approximately 9% of low-mass wide triples experience mergers or inspirals within 10 Gyr.

The rate of WD-WD collisions leading to Type Ia supernovae is comparable to other channels, but accounts for less than 0.1% of observed rates.

Galactic tides can catalyze mergers, potentially explaining the origin of blue stragglers and other stellar phenomena.

Abstract

Recent surveys show that wide ($>10^4$ AU) binaries and triples are abundant in the field. We study the long-term evolution of wide hierarchical triple systems and the role played by the Galactic tidal (GT) field. We find that when the timescales of the secular von-Ziepel-Lidov-Kozai and the GT oscillations are comparable, triple evolution becomes chaotic which leads to extreme eccentricities. Consequently, the close pericentre approaches of the inner-binary components lead to strong interactions, mergers and collisions. We use a novel secular evolution code to quantify the key parameters and carry out a population-synthesis study of low and intermediate-mass wide-orbit triples. We find that in $\sim9\%$ of low-mass wide-triples the inner main-sequence binaries collide or tidally-inspiral within $10\ \rm Gyr$, with direct collisions are $6$ times more likely to occur. For the intermediate-mass sample, $\sim7.6\%$ of the systems merge or inspiral with roughly equal probabilities. We discuss the relative fractions of different stellar merger/inspiral outcomes as a function of their evolutionary stage (Main-Sequence, MS; Red-Giant, RG; or White-Dwarf, WD), their transient electromagnetic signatures and the final products of the merger/inspiral. In particular, the rate of WD-WD direct-collisions that lead to type-Ia Supernovae is comparable to other dynamical channels and accounts for at most $0.1\%$ of the observed rate. RG inspirals provide a novel channel for the formation of eccentric common-envelope-evolution binaries. The catalysis of mergers/collisions in triples due to GT could explain a significant fraction, or even the vast majority, of blue-stragglers in the field, produce progenitors for cataclysmic-variables, and give-rise to mergers/collisions of double-RG binaries.