标题： 热力学对引力坍缩的影响：丝状结构的形成和磁场增强 显示英文标题

标题： The impact of thermodynamics on gravitational collapse: filament formation and magnetic field amplification

摘要： 恒星通过星际气体的引力坍缩形成。 气体的热力学响应可以通过一个有效状态方程来表征。 它决定了气体在被压缩时如何加热或冷却，因此在调节几乎所有尺度上的恒星形成过程方面起着关键作用，从单个星团到整个星系。 我们系统地研究了高红移恒星形成背景下热力学对引力坍缩的影响，但认为我们的发现也适用于当前分子云中的恒星形成。 我们考虑了一个多方状态方程，P = k rho^Gamma，其中既包括亚等温指数Gamma < 1，也包括超等温指数Gamma > 1。 我们发现这两种情况之间存在显著差异。 对于Gamma > 1，压力梯度会减缓收缩，并导致形成一个具有势能平衡和湍流的核心。 弱磁场会被强烈扭曲，并通过小尺度湍流发电机在对应于粘性尺度涡旋周转时间的时间尺度上高效放大。 而对于Gamma < 1，压力支撑不足以形成这样的核心。 引力收缩进行得更快，流动会产生非常强烈的激波，形成相互交叉的片状结构和延伸的丝状结构。 resulting 磁场线非常一致，并表现出相当程度的秩序。 然而，在这些条件下，我们仍然发现磁能密度在运动学阶段呈指数增长。 显示英文摘要

摘要： Stars form by the gravitational collapse of interstellar gas. The thermodynamic response of the gas can be characterized by an effective equation of state. It determines how gas heats up or cools as it gets compressed, and hence plays a key role in regulating the process of stellar birth on virtually all scales, ranging from individual star clusters up to the galaxy as a whole. We present a systematic study of the impact of thermodynamics on gravitational collapse in the context of high-redshift star formation, but argue that our findings are also relevant for present-day star formation in molecular clouds. We consider a polytropic equation of state, P = k rho^Gamma, with both sub-isothermal exponents Gamma < 1 and super-isothermal exponents Gamma > 1. We find significant differences between these two cases. For Gamma > 1, pressure gradients slow down the contraction and lead to the formation of a virialized, turbulent core. Weak magnetic fields are strongly tangled and efficiently amplified via the small-scale turbulent dynamo on timescales corresponding to the eddy-turnover time at the viscous scale. For Gamma < 1, on the other hand, pressure support is not sufficient for the formation of such a core. Gravitational contraction proceeds much more rapidly and the flow develops very strong shocks, creating a network of intersecting sheets and extended filaments. The resulting magnetic field lines are very coherent and exhibit a considerable degree of order. Nevertheless, even under these conditions we still find exponential growth of the magnetic energy density in the kinematic regime.