Interstellar MHD Turbulence and Star Formation
Interstellar MHD Turbulence and Star Formation
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星际 MHD 湍流和恒星形成
DOI：
10.1007/978-3-662-44625-6_14
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发表时间：
2012
期刊：
影响因子：
--
通讯作者：
E. Vázquez
中科院分区：
文献类型：
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作者：
E. Vázquez
本章回顾了银河系星际介质(ISM)中湍流的性质及其与恒星形成(SF)过程的联系。ISM是湍流的、磁化的、自引力的，并受到控制其热力学行为的加热和冷却过程的影响。ISM的热和热电离分量中的湍流似乎是跨音速或亚音速的，因此表现出几乎不可压缩的行为。然而，中性的热和冷成分是高度可压缩的，这既是原子气体中的热不稳定的结果，也是大致等温的冷原子和分子成分中中到强超音速运动的结果。在此背景下，我们讨论了：i)在等温和多向介质中湍流密度涨落的产生和统计分布；ii)热不稳定产生的团块的性质，注意到与经典观点相反，它们通常从其环境中吸收质量；iii)湍流密度涨落中的密度-磁场相关(或缺乏)，这是湍流中不同波模叠加的结果；iv)在密度涨落中质磁通量比(MFR)的演变，因为它们是由动态压缩形成的；v)在热不稳定性的帮助下形成冷密云；6)预期形成恒星的分子云可能正在经历全球引力收缩，而不是接近平衡，以及7)通过恒星反馈来调节这种引力收缩云中的恒星形成率(SFR)，而不是阻止云坍塌，而是在它们坍塌时蒸发和散布它们。
This chapter reviews the nature of turbulence in the Galactic interstellar medium (ISM) and its connections to the star formation (SF) process. The ISM is turbulent, magnetized, self-gravitating, and is subject to heating and cooling processes that control its thermodynamic behavior. The turbulence in the warm and hot ionized components of the ISM appears to be trans- or subsonic, and thus to behave nearly incompressibly. However, the neutral warm and cold components are highly compressible, as a consequence of both thermal instability in the atomic gas and of moderately-to-strongly supersonic motions in the roughly isothermal cold atomic and molecular components. Within this context, we discuss: i) the production and statistical distribution of turbulent density fluctuations in both isothermal and polytropic media; ii) the nature of the clumps produced by thermal instability, noting that, contrary to classical ideas, they in general accrete mass from their environment; iii) the density-magnetic field correlation (or lack thereof) in turbulent density fluctuations, as a consequence of the superposition of the different wave modes in the turbulent flow; iv) the evolution of the mass-to-magnetic flux ratio (MFR) in density fluctuations as they are built up by dynamic compressions; v) the formation of cold, dense clouds aided by thermal instability; vi) the expectation that star-forming molecular clouds are likely to be undergoing global gravitational contraction, rather than being near equilibrium, and vii) the regulation of the star formation rate (SFR) in such gravitationally contracting clouds by stellar feedback which, rather than keeping the clouds from collapsing, evaporates and diperses them while they collapse.