10,000 Resolved Triples from Gaia: Empirical Constraints on Triple Star Populations

TL;DR

This paper presents a catalog of approximately 10,000 resolved triple star systems within 500 parsecs, derived from Gaia data, and uses it to analyze the demographics, formation, and stability of triple star populations.

Contribution

The study provides the first large, well-characterized catalog of resolved triples, constrains their intrinsic properties, and offers a new model for generating mock populations based on empirical data.

Findings

Triples are compatible with hierarchical, stable configurations.

Orbital inclinations are isotropic for wide triples, modestly aligned in compact ones.

Inner binary properties mirror those of isolated binaries, including twin excess.

Abstract

We present a catalog of $\sim 10,000$ resolved triple star systems within 500 pc of the Sun, constructed using Gaia data. The triples include main-sequence, red giant, and white dwarf components spanning separations of 10 to 50,000 au. A well-characterized selection function allows us to constrain intrinsic demographics of the triple star population. We find that (a) all systems are compatible with being hierarchical and dynamically stable; (b) mutual orbital inclinations are isotropic for wide triples but show modest alignment as the systems become more compact; (c) primary masses follow a Kroupa initial mass function weighted by the triple fraction; (d) inner binary orbital periods, eccentricities, and mass ratios mirror those of isolated binaries, including a pronounced twin excess (mass ratios greater than 0.95) out to separations of 1000+ au, suggesting a common formation pathway; (e) tertiary mass ratios follow a power-law distribution with slope $-1.4$; (f) tertiary orbits are consistent with a log-normal period distribution and thermal eccentricities, subject to dynamical stability. Informed by these observations, we develop a publicly available prescription for generating mock triple star populations. Finally, we estimate the catalog's completeness and infer the intrinsic triple fraction, which rises steadily with primary mass: from $5\%$ at $\lesssim 0.5\,{\rm M_\odot}$ to $35\%$ at $2\,{\rm M_\odot}$. The public catalog provides a robust testbed for models of triple star formation and evolution.