Dynamical Evolution of White Dwarfs in Triples in the Era of Gaia

TL;DR

This study models the long-term evolution of white dwarf triples using Gaia data, revealing the importance of three-body dynamics and stellar evolution in forming close WD binaries and estimating the prevalence of triples among solar-type stars.

Contribution

It combines detailed simulations of triple star systems with Gaia observations to understand white dwarf evolution and the formation of compact binaries, highlighting the role of the eccentric Kozai-Lidov mechanism.

Findings

Mass loss-induced kicks are essential for matching Gaia WD triple distributions.

At least 30% of local solar-type stars originate from triple systems.

Three-body dynamics significantly influence WD binary formation and mergers.

Abstract

The $Gaia$ mission has detected many white dwarfs (WDs) in binary and triple configurations, and while observations suggest that triple stellar systems are common in our Galaxy, not much attention was devoted to WDs in triples. For stability reasons, these triples must have hierarchical configurations, i.e., two stars are on a tight orbit (the inner binary), with the third companion on a wider orbit about the inner binary. In such a system, the two orbits torque each other via the eccentric Kozai-Lidov mechanism (EKL), which can alter the orbital configuration of the inner binary. We simulate thousands of triple stellar systems for over $10$ Gyr, tracking gravitational interactions, tides, general relativity, and stellar evolution up to their WD fate. As demonstrated here, three-body dynamics coupled with stellar evolution is a critical channel to form tight WD binaries or merge a WD binary. Amongst these triples, we explore their manifestations as cataclysmic variables, Type Ia supernovae, and gravitational-wave events. The simulated systems are then compared to a sample of WD triples selected from the $Gaia$ catalog. We find that including the effect of mass loss-induced kicks is crucial for producing a distribution of the inner binary-tertiary separations that is consistent with $Gaia$ observations. Lastly, we leverage this consistency to estimate that, at minimum, $30\%$ of solar-type stars in the local $200$ parsecs were born in triples.