Wide-binary eccentricity distribution in young star clusters

Abstract

We study the wide-binary eccentricity (e) distribution in young star clusters and the role of turbulence in setting the form of the e distribution using magnetohydrodynamical simulations of star cluster formation. The simulations incorporate gravity, turbulence, magnetic fields, protostellar heating, and jets/outflows. We find that (1) simulations that employ purely compressive turbulence driving produce binaries with a superthermal e distribution [in], while simulations with purely solenoidal driving or natural mixture of driving modes produce subthermal/thermal distributions (1), (2) the e distribution over the full range of binary separations in our simulations is set at the early stages of the star cluster formation process, (3) while binaries (separation of) have subthermal to thermal e distributions (), wide binaries () have a superthermal distribution (), and (4) low-mass binary systems (system masses of) have a highly superthermal distribution (), whereas high-mass systems () exhibit a subthermal/thermal distribution (). The binary eccentricity distribution is often modelled as a thermal distribution. However, our results suggest that the e distribution depends on the range of separation of the sampled binaries, which agrees with the findings from recent Gaia observations. We conclude that the dependence of the e distribution on the binary separation and mass is linked to the binary formation mechanism governed by the turbulent properties of the parent cloud. Show more