The eccentricity distribution of wide binaries and their individual measurements

Eccentricity of wide binaries is difficult to measure due to their long orbital periods. With Gaia's high-precision astrometric measurements, eccentricity of a wide binary can be constrained by the angle between the separation vector and the relative velocity vector (the v-r angle). In this paper, by using the v-r angles of wide binaries in Gaia Early Data Release 3, we develop a Bayesian approach to measure the eccentricity distribution as a function of binary separations. Furthermore, we infer the eccentricities of individual wide binaries and make them publicly available. Our results show that the eccentricity distribution of wide binaries at 10(2) AU is close to uniform and becomes superthermal at >10(3) AU, suggesting two formation mechanisms dominating at different separation regimes. The close binary formation, most likely disc fragmentation, results in a uniform eccentricity distribution at 10(3) AU may be turbulent fragmentation and/or the dynamical unfolding of compact triples. With Gaia, measuring eccentricities is now possible for a large number of wide binaries, opening a new window to understanding binary formation and evolution.

Automated summary

This paper develops a Bayesian approach to measure the eccentricity distribution of wide binaries based on high-precision astrometric measurements from the Gaia satellite. The results reveal two different formation mechanisms dominating at different separation regimes, providing a new perspective for understanding binary formation and evolution.