Streaming Instabilities in Protoplanetary Disks
Streaming Instabilities in Protoplanetary Disks
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DOI：
10.1086/426895
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发表时间：
2004-09
期刊：
影响因子：
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通讯作者：
A. Youdin;J. Goodman
中科院分区：
文献类型：
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作者：
A. Youdin;J. Goodman
开普勒盘中相互穿透的固体流和气体流产生局部的线性不稳定性。这两个组件通过气动阻力相互作用，产生径向漂移并触发不稳定模式。这种长期的不稳定性不需要自重，但它会产生越来越大的粒子密度扰动，这可能会催生小行星的形成。增长速度慢于动态，但快于径向漂移时标。与流动速度一样，增长速度对于边际耦合(停止时间与动态时间相当)也是最大的。当固气密度比为有序单位且反馈最强时，增长最快。奇怪的是，当密度太接近时，增长会受到强烈抑制。类比霍华德半圆定理，解释了背景漂移与波性质的关系。三维双流体方程描述了六阶(复频率)的色散关系。终端速度近似允许简化为近似的立方色散关系。为了描述这种不稳定性的最简单表现，我们忽略了复杂的(但可能是相关的)因素，如垂直分层、颗粒大小分散、湍流和自重。我们考虑在小行星形成中的应用，并将我们的工作与粒子-气体动力学的其他研究进行比较。
Interpenetrating streams of solids and gas in a Keplerian disk produce a local, linear instability. The two components mutually interact via aerodynamic drag, which generates radial drift and triggers unstable modes. The secular instability does not require self-gravity, yet it generates growing particle-density perturbations that could seed planetesimal formation. Growth rates are slower than dynamical but faster than radial drift timescales. Growth rates, like streaming velocities, are maximized for marginal coupling (stopping times comparable to dynamical times). Fastest growth occurs when the solid-to-gas density ratio is order unity and feedback is strongest. Curiously, growth is strongly suppressed when the densities are too nearly equal. The relation between background drift and wave properties is explained by analogy with Howard's semicircle theorem. The three-dimensional, two-fluid equations describe a sixth-order (in the complex frequency) dispersion relation. A terminal velocity approximation allows simplification to an approximate cubic dispersion relation. To describe the simplest manifestation of this instability, we ignore complicating (but possibly relevant) factors such as vertical stratification, dispersion of particle sizes, turbulence, and self-gravity. We consider applications to planetesimal formation and compare our work to other studies of particle-gas dynamics.