English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

GAIA wide stellar binaries (semimajor axes $\gtrsim 10^3\,\mathrm{AU}$) havea superthermal eccentricity distribution function (DF), well-fit by $P(e)\propto e^\alpha$ with $\alpha \sim 1.2$. In Paper I, we proved that this DFcannot have been produced by Galactic tidal torques starting from any realisticDF that was not already superthermal. Here, we consider the other majordynamical effect on wide binaries: encounters with passing stars. We derive andsolve the Fokker-Planck equation governing the evolution of binaries insemimajor axis and eccentricity under many weak, impulsive, penetrative stellarencounters. We show analytically that these encounters drive the eccentricityDF towards thermal on the same timescale as they drive the semimajor axes $a$towards ionization, $t_\mathrm{ion} \sim4\,\mathrm{Gyr}\,(a/10^4\,\mathrm{AU})^{-1}$. We conclude that the observedsuperthermal DF must derive from an even more superthermal (i.e. higher$\alpha$) birth distribution. This requirement rules out the possibility thatmost wide binaries are formed via e.g. the dissolution of stellar clusters, andinstead favors a turbulent fragmentation scenario. A testable prediction of ourtheory is that $\alpha$ should be a monotonically decreasing function of binaryage.

Eccentricity dynamics of wide binaries -- II. The effect of stellar encounters and constraints on formation channels