吸积驱动的Turbulence作为普遍过程：星系、分子云和原恒星的碰撞
Accretion-Driven Turbulence as Universal Process: Galaxies, Molecular Clouds, and Protostellar Disks
摘要：
复杂的湍流运动在许多天体物理系统中普遍存在。然而，它们的起源仍然知之甚少。当宇宙结构形成时，它们通过周围环境的吸积而大量增长。我们认为这种吸积能够驱动广泛的天体物理物体的内部湍流运动，并在星系、分子云和原行星盘的情况下研究这一过程。我们使用的数值模拟和分析参数相结合来预测的湍流水平的吸积率，耗散尺度和密度对比度的函数，并与观测数据进行比较。我们发现，在银河系型星系中观测到的星际介质中的湍流水平可以用吸积来解释，只要星系获得质量的速率与它们形成恒星的速率相当。这一过程在恒星形成半径以外的扩展外盘中尤为重要。我们还计算了分子云从星系气体的原子成分中形成时质量增长的速率，并发现它们的内部湍流也可能是由吸积驱动的。正是云的形成过程通过建立湍流级联激发了小尺度的湍流运动。在金牛座T盘的情况下，我们表明，吸积可以驱动亚音速湍流在观察到的水平，如果气体落在磁盘上的速度是可比的磁盘材料吸积到中央恒星的速度。这也解释了观测到的吸积率与恒星质量的关系dM/dt ~ M ^[1.8]。在所有三种情况下，将下落运动转化为湍流所需的效率都在百分之几的量级。我们的结论是，吸积驱动的湍流是一个普遍的概念，具有深远的影响，广泛的天体物理对象。
英文摘要：
Complex turbulent motions are ubiquitously observed in many astrophysical systems. Their origin, however, is still poorly understood. When cosmic structures form, they grow in mass via accretion from the surrounding environment. We propose that this accretion is able to drive internal turbulent motions in a wide range of astrophysical objects and study this process in the case of galaxies, molecular clouds and protoplanetary disks. We use a combination of numerical simulations and analytical arguments to predict the level of turbulence as a function of the accretion rate, the dissipation scale, and the density contrast, and compare with observational data. We find that in Milky Way type galaxies the observed level of turbulence in the interstellar medium can be explained by accretion, provided that the galaxies gain mass at a rate comparable to the rate at which they form stars. This process is particularly relevant in the extended outer disks beyond the star-forming radius. We also calculate the rate at which molecular clouds grow in mass when they build up from the atomic component of the galactic gas and find that their internal turbulence is likely to be driven by accretion as well. It is the very process of cloud formation that excites turbulent motions on small scales by establishing the turbulent cascade. In the case of T Tauri disks, we show that accretion can drive subsonic turbulence at the observed level if the rate at which gas falls onto the disk is comparable to the rate at which disk material accretes onto the central star. This also explains the observed relation of accretion rate and stellar mass, dM/dt ~ M^1.8. The efficiency required to convert infall motion into turbulence is of the order of a few percent in all three cases. We conclude that accretion-driven turbulence is a universal concept with far-reaching implications for a wide range of astrophysical objects.
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