Alignment physics of disks warped by Lense–Thirring precession
Alignment physics of disks warped by Lense–Thirring precession
复制标题
因 Lense-Thirring 进动而扭曲的圆盘的对准物理
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
J. Hawley
中科院分区：
文献类型：
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作者：
J. Krolik;K. Sorathia;J. Hawley
吸积盘出现在各种各样的天体物理背景下，从行星形成到黑洞的吸积。为了简单起见，它们通常被想象成又薄又平。然而，每当圆盘的角动量与中心物体的角动量倾斜时，圆盘内的环就会产生扭矩，使其进动、扭曲和翘曲。由于扭矩随着半径的增加而迅速减弱，长期以来人们一直认为，一些未指明的“摩擦”使这些圆盘的内部部分对齐，而外部部分保持在原来的方向。几乎所有关于这一主题的先前工作都假设这样一个圆盘的内应力可以用各向同性粘度来描述，尽管40多年来人们已经知道，流体粘度太弱，在吸积盘中不重要，而且20年来吸积应力实际上是由各向异性MHD湍流引起的。本文回顾了最近的数值模拟工作，显示了当扭曲盘的力学仅用实际力（包括MHD湍流）来描述时，扭曲盘是如何排列的。确定了排列的详细机制，量化了排列发生的速率，并表明各向同性粘度模型与模拟数据存在严重分歧。
Accretion disks occur in a wide variety of astrophysical contexts, from planet formation to accretion onto black holes. For simplicity, they are generally imagined as thin and flat. However, whenever the diskʼs angular momentum is oblique to the angular momentum of the central object(s), a torque causes rings within the disk to precess, twisting and warping it. Because the torque weakens rapidly with increasing radius, it has long been thought that some unspecified ‘friction’ brings the inner portions of such disks into alignment, while the outer parts remain in their original orientation. Nearly all previous work on this topic has assumed that such a diskʼs internal stresses can be described by an isotropic viscosity, even though it has been known for more than four decades that fluid viscosity is far too weak to be significant in accretion disks, and for two decades that accretion stresses are actually due to anisotropic MHD turbulence. This paper reviews recent numerical simulation work showing how twisted disks align when their mechanics are described only in terms of real forces, including MHD turbulence. The detailed mechanisms of alignment are identified, the rate at which it occurs is quantified, and the isotropic viscosity model is shown to be in drastic disagreement with the simulation data.