The formation of very wide binaries

TL;DR

This paper proposes a new formation mechanism for very wide binaries in the Galactic field, suggesting they originate from dissolving star clusters rather than star formation or dynamical interactions.

Contribution

It introduces a model where wide binaries form during cluster dissolution and uses N-body simulations to explore their properties and prevalence.

Findings

Wide binary fraction per cluster is 1-30%.

Many wide binaries are part of wider multiple systems.

Formation depends on initial cluster conditions.

Abstract

Over the last decades, numerous wide (>1000 AU) binaries have been discovered in the Galactic field and halo. The origin of these wide binaries cannot be explained by star formation or by dynamical interactions in the Galactic field. We explain their existence by wide binary formation during the dissolution phase of young star clusters. In this scenario, two single stars that leave the dissolving cluster at the same time, in the same direction, and with similar velocities, form a new, very wide binary. Using N-body simulations we study how frequently this occurs, and how the orbital parameters of such binaries depend on the properties of the cluster from which they originate. The resulting wide binary fraction for individual star clusters is 1-30%, depending on the initial conditions. As most stars form as part of a binary or multiple system, we predict that a large fraction of these wide binaries are in fact wide triple and quadruple systems.