Creation/destruction of ultra-wide binaries in tidal streams

Abstract

This paper uses statistical and $N$-body methods to explore a new mechanism to form binary stars with extremely large separations ($>0.1\mathrm{pc}$), whose origin is poorly understood. Here, ultra-wide binaries arise via chance entrapment of unrelated stars in tidal streams of disrupting clusters. It is shown that (i) the formation of ultra-wide binaries is not limited to the lifetime of a cluster, but continues after the progenitor is fully disrupted, (ii) the formation rate is proportional to the local phase-space density of the tidal tails, (iii) the semimajor axis distribution scales as $p(a)da\sim a^{1/2}da$ at $a\ll D$, where $D$ is the mean interstellar distance, and (vi) the eccentricity distribution is close to thermal, $p(e)de=2ede$. Owing to their low binding energies, ultra-wide binaries can be disrupted by both the smooth tidal field and passing substructures. The time-scale on which tidal fluctuations dominate over the mean field is inversely proportional to the local density of clumps. Monte-Carlo experiments show that binaries subject to tidal evaporation follow $p(a)da\sim a^{-1}da$ at $a\gtrsim a_{\mathrm{peak}}$, known as Öpik's law, with a peak semi-major axis that contracts with time as $a_{\mathrm{peak}}\sim t^{-3/4}$. In contrast, a smooth Galactic potential introduces a sharp truncation at the tidal radius, $p(a)\sim 0$ at $a\gtrsim r_t$. The scaling relations of young clusters suggest that most ultra-wide binaries arise from the disruption of low-mass systems. Streams of globular clusters may be the birthplace of hundreds of ultra-wide binaries, making them ideal laboratories to probe clumpiness in the Galactic halo.

17 pages, 11 figures. Accepted to MNRAS

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Cited by in corpus (10)

• Eccentricity dynamics of wide binaries -- I. The effect of Galactic tides
• On the phase-mixed eccentricity and inclination distributions of wide binaries in the Galaxy
• The consistency of chemical clocks among coeval stars
• A halo of trapped interstellar matter surrounding the solar system
• Wide binaries from the H3 survey: the thick disk and halo have similar wide binary fractions
• The breakdown of current gyrochronology as evidenced by old coeval stars
• Evolution of binary stars in the early evolutionary phases of ultra-faint dwarf galaxies
• Two-Point Separation Functions for Modeling Wide Binary Systems in Nearby Dwarf Galaxies
• Chemodynamics of metal-poor wide binaries in the Galactic halo: Association with the Sequoia event
• Stellar Mass Segregation in Dark Matter Halos