A NEW JEANS RESOLUTION CRITERION FOR (M)HD SIMULATIONS OF SELF-GRAVITATING GAS: APPLICATION TO MAGNETIC FIELD AMPLIFICATION BY GRAVITY-DRIVEN TURBULENCE
A NEW JEANS RESOLUTION CRITERION FOR (M)HD SIMULATIONS OF SELF-GRAVITATING GAS: APPLICATION TO MAGNETIC FIELD AMPLIFICATION BY GRAVITY-DRIVEN TURBULENCE
复制标题
自重力气体 (M)HD 模拟的新 Jean 分辨率准则：在重力驱动湍流磁场放大中的应用
DOI：
10.1088/0004-637x/731/1/62
复制
发表时间：
2011
期刊：
影响因子：
--
通讯作者：
Ralf S. Klessen
中科院分区：
文献类型：
--
作者：
Christoph Federrath;Sharanya Sur;Dominik R. G Schleicher;Robi Banerjee;Ralf S. Klessen
宇宙结构的形成是以重力、湍流和磁场之间复杂的相互作用为特征的。然而，人们对引力能转化为湍流能和磁能的过程仍然知之甚少。在这里，我们显示与高分辨率，自适应网格模拟，MHD湍流是有效地驱动提取能量的重力势在致密的气体云的崩溃。在收缩过程中产生的可压缩运动被转换成螺线管，湍流运动，导致自然能量比E sol/E tot 2/3。我们发现，引力驱动湍流的能量注入尺度接近于局域的金斯尺度。如果磁场的小种子存在，它们通过小尺度发电机过程以指数速度放大。磁场在最小的尺度上增长最有效，因为磁力线的拉伸、扭曲和折叠以及湍流涡旋都能充分分辨。我们发现，这个规模对应于约30个网格单元的模拟。因此，我们建议一个新的最小分辨率标准的30个细胞每牛仔裤长度（磁）流体动力学模拟的自引力气体，以解决湍流的牛仔裤规模，并捕捉最小的发电机放大的磁场。然而，由于数值扩散，今天任何现有的模拟最多只能提供物理增长率的下限。我们的结论是，一个小的，初始磁场可以增长到动态的重要强度的时间尺度上显着短于云的自由落体时间。
Cosmic structure formation is characterized by the complex interplay between gravity, turbulence, and magnetic fields. The processes by which gravitational energy is converted into turbulent and magnetic energies, however, remain poorly understood. Here, we show with high-resolution, adaptive-mesh simulations that MHD turbulence is efficiently driven by extracting energy from the gravitational potential during the collapse of a dense gas cloud. Compressible motions generated during the contraction are converted into solenoidal, turbulent motions, leading to a natural energy ratio of E sol/E tot≈ 2/3. We find that the energy injection scale of gravity-driven turbulence is close to the local Jeans scale. If small seeds of the magnetic field are present, they are amplified exponentially fast via the small-scale dynamo process. The magnetic field grows most efficiently on the smallest scales, for which the stretching, twisting, and folding of field lines, and the turbulent vortices are sufficiently resolved. We find that this scale corresponds to about 30 grid cells in the simulations. We thus suggest a new minimum resolution criterion of 30 cells per Jeans length in (magneto) hydrodynamical simulations of self-gravitating gas, in order to resolve turbulence on the Jeans scale, and to capture minimum dynamo amplification of the magnetic field. Due to numerical diffusion, however, any existing simulation today can at best provide lower limits on the physical growth rates. We conclude that a small, initial magnetic field can grow to dynamically important strength on timescales significantly shorter than the free-fall time of the cloud.
登录
查看更多内容
DOI：
--
发表时间：
2003
期刊：
影响因子：
--
作者：
C. Brunt;M. Heyer;E. Vázquez;B. Pichardo
通讯作者：
B. Pichardo
DOI：
10.1088/2041-8205/721/2/l134
发表时间：
2010
期刊：
The Astrophysical Journal Letters
影响因子：
--
作者：
Sharanya Sur;Dominik R. G. Schleicher;Robi Banerjee;Christoph Federrath;Ralf S. Klessen
通讯作者：
Ralf S. Klessen
H 3 冷却对于原始气体是否重要？
DOI：
10.1111/j.1365-2966.2008.14156.x
发表时间：
2008
影响因子：
4.8
作者：
S. Glover;D. Savin
通讯作者：
D. Savin
湍流分子云中恒星团的形成：状态方程的影响
DOI：
10.1086/375780
发表时间：
2002
期刊：
The Astrophysical Journal
影响因子：
--
作者：
Yue;R. Klessen;M. Mac Low
通讯作者：
M. Mac Low
DOI：
10.1086/183824
发表时间：
1982
期刊：
The Astrophysical Journal
影响因子：
--
作者：
J. Scalo;W. Pumphrey
通讯作者：
W. Pumphrey