The Evolution of Wide Binary Stars

TL;DR

This paper investigates how wide binary stars evolve under gravitational influences, revealing a characteristic density minimum and a long-range correlation in star positions and velocities detectable by surveys like GAIA.

Contribution

It models the orbital evolution of wide binaries considering Galactic tides and stellar encounters, identifying a density minimum and long-range correlations in star distributions.

Findings

Number density exhibits a minimum at a few times the Jacobi radius.

A density peak at 100-300 pc separation arises from drifting apart binaries.

Long-range correlations in star positions and velocities are detectable in astrometric surveys.

Abstract

We study the orbital evolution of wide binary stars in the solar neighborhood due to gravitational perturbations from passing stars. We include the effects of the Galactic tidal field and continue to follow the stars after they become unbound. For a wide variety of initial semi-major axes and formation times, we find that the number density (stars per unit logarithmic interval in projected separation) exhibits a minimum at a few times the Jacobi radius r_J, which equals 1.7 pc for a binary of solar-mass stars. The density peak interior to this minimum arises from the primordial distribution of bound binaries, and the exterior density, which peaks at \sim 100--300 pc separation, arises from formerly bound binaries that are slowly drifting apart. The exterior peak gives rise to a significant long-range correlation in the positions and velocities of disk stars that should be detectable in large astrometric surveys such as GAIA that can measure accurate three-dimensional distances and velocities.