The Dynamical Significance of Triple Star Systems in Star Clusters

TL;DR

This paper demonstrates that triple star systems play a significant dynamical role in star clusters, with encounters involving triples occurring as frequently as those involving singles or binaries, especially in low-mass clusters.

Contribution

It provides an analysis of the dynamical importance of triples in star clusters using empirical data, highlighting their potential influence on astrophysical phenomena.

Findings

Triple-involving encounters occur as often as single or binary encounters in low-mass clusters.

The cross section for stellar encounters increases with multiplicity.

Triples may significantly impact the evolution of star clusters and related astrophysical processes.

Abstract

Over the last few decades, observational surveys have revealed that high-order multiple-star systems (e.g. triples, quadruples, etc.), and triples in particular, are common in our Galaxy. In this paper, we consider the dynamical significance of this transformation in our understanding of stellar multiplicity. Using empirically constrained binary and triple fractions in those star clusters for which these values are available in the literature, we compare analytic rates for encounters involving single, binary, and triple stars. Our results show that, \textit{even for relatively low triple fractions, dynamical interactions involving triples occur roughly as often as encounters involving either single or binary stars alone, particularly in low-mass star clusters}. More generally, using empirically-derived multiple star catalogues for the young star-forming association Taurus-Auriga and the Galactic field, we show that the data are consistent with the gravitationally-focused cross section for encounters increasing with increasing multiplicity. Consequently, triple stars, and even higher-order multiples, could be more important than previously realized for a number of astrophysical phenomena, including the formation and destruction of compact binaries and various types of stellar exotica, and the dynamical evolution of star clusters.