The origin of very wide binary systems

TL;DR

This paper investigates the origins of extremely wide binary star systems, proposing they form during star cluster dissolution and supporting this with N-body simulations, which predict a significant fraction of wide binaries are actually multiple systems.

Contribution

It introduces a novel hypothesis that wide binaries originate from star cluster dissolution and validates it through N-body simulations showing plausible wide binary fractions.

Findings

Wide binary fractions range from 1% to 30% depending on initial conditions.

Most wide 'binaries' are likely multiple systems.

Formation during cluster dissolution explains the existence of very wide binaries.

Abstract

The majority of stars in the Galactic field and halo are part of binary or multiple systems. A significant fraction of these systems have orbital separations in excess of thousands of astronomical units, and systems wider than a parsec have been identified in the Galactic halo. These binary systems cannot have formed through the 'normal' star-formation process, nor by capture processes in the Galactic field. We propose that these wide systems were formed during the dissolution phase of young star clusters. We test this hypothesis using N-body simulations of evolving star clusters and find wide binary fractions of 1-30%, depending on initial conditions. Moreover, given that most stars form as part of a binary system, our theory predicts that a large fraction of the known wide 'binaries' are, in fact, multiple systems.