This paper uses statistical and $N$-body methods to explore a new mechanism to form binary stars with extremely large separations ($> 0.1\,{\rm pc}$), 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 $p(a)d a\sim a^{1/2}d a$ at $a\ll D$, where $D$ is the mean interstellar distance, and (vi) the eccentricity distribution is close to thermal, $p(e)d e= 2 e d e$. 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 $p(a)d a\sim a^{-1}d a$ at $a\gtrsim a_{\rm peak}$, known as Opik's law, with a peak semi-major axis that contracts with time as $a_{\rm peak}\sim t^{-3/4}$. 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.

中文翻译：

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潮汐流中超宽双星的产生/破坏

本文使用统计方法和$N$-body方法探索了一种形成具有极大间距（$> 0.1\,{\rm pc}$）的双星的新机制，其起源知之甚少。在这里，超宽双星是通过在扰乱星团的潮汐流中偶然捕获无关恒星而产生的。结果表明，（i）超宽双星的形成不仅限于星团的生命周期，而是在前身星被完全破坏后继续形成，（ii）形成速率与团簇的局部相空间密度成正比。潮汐尾，(iii) 长半轴分布尺度为 $p(a)da\sim a^{1/2}da$ 在 $a\ll D$，其中 $D$ 是平均星际距离，以及 (vi ) 偏心率分布接近热分布，$p(e)de= 2 ede$。由于它们的结合能低，超宽双星可以被平滑的潮汐场和经过的子结构破坏。潮汐波动在平均场上占主导地位的时间尺度与局部的团块密度成反比。蒙特卡罗实验表明，受潮汐蒸发影响的双星在 $a\gtrsim a_{\rm peak}$ 处遵循 $p(a)da\sim a^{-1}da$，称为 Opik 定律，峰值半- 长轴随着时间收缩为 $a_{\rm peak}\sim t^{-3/4}$。相比之下，平滑的银河势在潮汐半径处引入了急剧的截断，$p(a)\sim 0$ 在 $a\gtrsim r_t$。年轻星团的标度关系表明，大多数超宽双星来自低质量系统的破坏。球状星团流可能是数百个超宽双星的诞生地，