Disc formation in turbulent cloud cores: is magnetic flux loss necessary to stop the magnetic braking catastrophe or not?
Disc formation in turbulent cloud cores: is magnetic flux loss necessary to stop the magnetic braking catastrophe or not?
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湍流云核中的圆盘形成：磁通量损失是否有必要阻止磁制动灾难？
DOI：
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发表时间：
2012
期刊：
影响因子：
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通讯作者：
A. Lazarian
中科院分区：
文献类型：
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作者：
R. Santos;E. Pino;A. Lazarian
Santos-Lima、de Gouveia Dal Pino 和 Lazarian (2012) 最近对湍流磁化云核中的开普勒圆盘形成进行的数值分析表明，重联扩散是在旋转支撑圆盘形成过程中去除多余磁通量的有效过程。这个过程是由湍流中磁场的快速重新连接引起的。在一项类似的数值研究中，Seifried 等人。 (2012) 得出的结论是，重联扩散或任何其他非理想 MHD 效应都是不必要的，单独的湍流剪切将提供一种自然的方式来构建旋转盘，而不需要磁通量损失。他们的结论基于这样一个事实：在半径远大于圆盘的球形区域上评估的平均质量通量比 (μ) 在他们的模型中几乎是恒定的。在这封信中，我们比较了两组模拟，并表明这种大尺度的平均可以掩盖磁盘形成的内部区域中 µ 的显着实际增加。我们证明，湍流引起的磁场重联扩散发生在正在吸积的湍流包络材料中盘形成的初始阶段。我们的分析表明重联扩散存在于两组模拟中，并为文献中讨论的与原恒星吸积盘形成相关的“磁制动灾难”提供了一个简单的解决方案。
Recent numerical analysis of Keplerian disk formation in turbulent, magnetized cloud cores by Santos-Lima, de Gouveia Dal Pino, & Lazarian (2012) demonstrated that reconnection diffusion is an efficient process to remove the magnetic flux excess during the build up of a rotationally supported disk. This process is induced by fast reconnection of the magnetic fields in a turbulent flow. In a similar numerical study, Seifried et al. (2012) concluded that reconnection diffusion or any other non-ideal MHD effects would not be necessary and turbulence shear alone would provide a natural way to build up a rotating disk without requiring magnetic flux loss. Their conclusion was based on the fact that the mean mass-to-flux ratio (µ) evaluated over a spherical region with a radius much larger than the disk is nearly constant in their models. In this letter we compare the two sets of simulations and show that this averaging over large scales can mask significant real increases of µ in the inner regions where the disk is built up. We demonstrate that turbulence-induced reconnection diffusion of the magnetic field happens in the initial stages of the disk formation in the turbulent envelope material that is accreting. Our analysis is suggestive that reconnection diffusion is present in both sets of simulations and provides a simple solution for the “magnetic braking catastrophe” which is discussed in the literature in relation to the formation of protostellar accretion disks.