Astrophysical fluid dynamics

磁场在宇宙中几乎无处不在，在高能粒子的产生、黑洞气体的吸积以及恒星的形成中起着至关重要的作用。然而，关于它们的起源存在相当大的争议，关于它们的行为也存在同样多的不确定性，这反过来意味着我们对各种天体物理现象的理解存在很大的不确定性。人们普遍认为，磁场的起源和演化与星际介质和恒星内部气体的湍流运动密切相关。在此，我们建议研究与磁场和恒星形成有关的几个关键过程。其中之一是导电流体中磁场形成的一般过程（即发电机活动），这意味着几乎所有的热气体，包括恒星、吸积盘和星际介质。这与星系磁场的起源直接相关，特别是星系形成后是否会迅速产生强大而组织良好的磁场的问题，正如观测表明的那样，或者我们是否必须诉诸早期宇宙中的奇异物理过程来理解星系磁场的演化。其次，如果我们把磁场想象成由“场线”组成，那么一个普遍注意到的悖论是，这些场线似乎“重新连接”，或转换附件，在恒星内外都没有太大困难。尽管在理解低密度环境（如星际介质）中的磁重联方面已经做了大量的工作，但这些工作并不能帮助我们理解恒星内部的磁重联。我一直在研究湍流对这一过程的影响，并将进行一系列的数值实验来测试之前发表的关于湍流中快速磁重联的想法。第三，我将把发电机和重联的工作应用于磁碟中磁场的产生和传输，这对类星体和恒星的形成至关重要。最后，我将研究在恒星形成的早期阶段磁场和流体不稳定性之间的相互作用。

Magnetic fields are found almost everywhere in the universe, and play a vital role in the creation of high energy particles, the accretion of gas onto black holes, and the formation of stars. Nevertheless there is considerable controversy regarding their origins and an equal amount of uncertainty with regard to their behavior, which in turn implies a great deal of uncertainty in our understanding of a wide variety of astrophysical phenomena. There is general agreement that the origin and evolution of magnetic fields are closely tied to the turbulent motions of gas in the interstellar medium and inside stars. Here we propose to study several key processes connected to magnetic fields and star formation. One of these is the general process of magnetic field formation (i.e. dynamo activity) in conducting fluids, which means almost all hot gases including stars, accretion disks and the interstellar medium. This is directly connected to the origin of galactic magnetic fields and in particular the question of whether or not strong and well organized fields arise quickly once galaxies form, as observations indicate, or whether we must appeal to exotic physical processes in the early universe to understand the evolution of galactic magnetic fields. Second, if we visualize magnetic fields as composed of "field lines" then a commonly noted paradox is that these field lines appear to "reconnect", or switch attachments, without much difficulty both inside and outside of stars. Although there has been a great deal of work on undrstanding magnetic reconnection in low density environments, like the interstellar medium, this work does not help us understand magnetic reconnection inside stars. I have been studying the effects of turbulence on this process and will conduct a series of numerical experiments to test previously published ideas on fast magnetic reconnection in turbulent fluids. Third, I will apply the work on dynamos and reconnection to the generation and transport of magnetic fields in disks, which are critical for quasars and star formation. Finally, I will examine the interplay between magnetic fields and fluid instabilities in the early stages of star formation.