发表机构
Nordita, KTH Royal Institute of Technology and Stockholm University; The Oskar Klein Centre, Department of Astronomy, Stockholm University; McWilliams Center for Cosmology & Department of Physics, Carnegie Mellon University; School of Natural Sciences and Medicine, Ilia State University; Scuola Normale Superiore; Argelander-Institut für Astronomie, Universität Bonn（诺迪塔，皇家理工学院和斯德哥尔摩大学; 奥斯卡·克莱因中心，天文学系，斯德哥尔摩大学; 麦克威廉斯宇宙学中心与物理系，卡内基梅隆大学; 自然科学与医学院，伊利亚州立大学; 比萨高等师范学院; 阿尔根德天文学研究所，波恩大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
通过数值模拟研究引力坍缩中涡量的产生效率，发现涡量仅来自初始无旋湍流而非坍缩流，不支持小尺度发电机所需的涡旋湍流。
AI 中文摘要
引力坍缩产生大量动能，可能引发湍流。如果这种湍流也适合启动发电机作用，产生的磁场将进一步改变动力学，尤其是在小尺度上。然而，小尺度发电机需要涡旋湍流，而坍缩主要产生无旋运动，这可能对发电机作用效率不高。在这里，我们研究了湍流坍缩过程中涡量的产生效率。我们使用正压状态方程，其中压力和密度梯度平行，且没有磁场，因此涡量只能由粘性产生。通过引力坍缩的直接数值模拟，我们表明，对于我们的数值分辨率可访问的参数空间，这种效应与初始无旋湍流有关，而不是坍缩流的结果。
英文摘要
Gravitational collapse creates large amounts of kinetic energy that could potentially seed turbulence. If such turbulence were also suitable to initiate dynamo action, the resulting magnetic field would further modify the dynamics, especially on small length scales. However, a small-scale dynamo is believed to require vortical turbulence, whereas the collapse produces mainly irrotational motions, which may not be efficient for dynamo action. Here, we study the efficiency of vorticity production during a turbulent collapse. We adopt a barotropic equation of state, where pressure and density gradients are parallel, and no magnetic field, so that vorticity can only be produced by viscosity and by vortex dynamo-type amplification. Using direct numerical simulations of gravitational collapse, we show that, for the parameter space accessible to our numerical resolution, these effects are related to the initial irrotational turbulence and are not induced by the collapse. Vorticity production along with the associated small-scale dynamo action are still expected to occur for sufficiently large Reynolds numbers, especially when baroclinic effects are allowed for, but some of the earlier numerical evidence in the literature using a barotropic equation of state is now found to be the result of subgrid scale modeling and not reproduced in direct numerical simulations.
Comments15 pages, 14 figures, 1 table, resubmitted to ApJ
