ON THE GRAVITATIONAL STABILITY OF GRAVITO-TURBULENT ACCRETION DISKS
ON THE GRAVITATIONAL STABILITY OF GRAVITO-TURBULENT ACCRETION DISKS
复制标题
引力湍流吸积盘的引力稳定性
DOI：
10.3847/0004-637x/824/2/91
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
K. Kratter
中科院分区：
文献类型：
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作者：
M. Lin;K. Kratter
低质量的自引力吸积盘允许准稳定的“引力-湍流”状态，在这种状态下，冷却平衡了湍流的粘性加热。然而，数值模拟表明，重力湍流不能持续超过动力学时间尺度时，冷却速率或相应的湍流粘度太大。结果是磁盘碎片。我们激励和量化的解释磁盘碎片无法保持重力湍流由于正式的二次不稳定性驱动：（1）冷却，减少压力支持;和/或（2）粘度，减少旋转支持。我们分析了轴对称的引力稳定性的粘性，非绝热吸积盘与内部加热，外部照射，和冷却的剪切盒近似。我们认为参数化的冷却功能在2D和3D磁盘，以及在3D辐射扩散。我们表明，一般没有临界冷却速率/粘度低于该磁盘是正式稳定的，虽然有趣的限制出现不稳定的模式与长度尺度上的磁盘厚度的顺序。我们应用这个新的线性理论的原行星盘重力湍流建模为一个有效的粘度，和冷却调节尘埃不透明度。我们发现，粘度使磁盘超过600 Au动态不稳定的径向尺度上的几倍，当地磁盘厚度。这与基于最大可持续应力的磁盘碎片化的经验条件是一致的。我们建议湍流应力可以发挥积极的作用，在现实的磁盘碎片通过消除旋转稳定对自引力，和所观察到的过渡行为从重力湍流碎片可能反映不稳定的重力湍流状态本身。
Low mass, self-gravitating accretion disks admit quasi-steady, “gravito-turbulent” states in which cooling balances turbulent viscous heating. However, numerical simulations show that gravito-turbulence cannot be sustained beyond dynamical timescales when the cooling rate or corresponding turbulent viscosity is too large. The result is disk fragmentation. We motivate and quantify an interpretation of disk fragmentation as the inability to maintain gravito-turbulence due to formal secondary instabilities driven by: (1) cooling, which reduces pressure support; and/or (2) viscosity, which reduces rotational support. We analyze the axisymmetric gravitational stability of viscous, non-adiabatic accretion disks with internal heating, external irradiation, and cooling in the shearing box approximation. We consider parameterized cooling functions in 2D and 3D disks, as well as radiative diffusion in 3D. We show that generally there is no critical cooling rate/viscosity below which the disk is formally stable, although interesting limits appear for unstable modes with lengthscales on the order of the disk thickness. We apply this new linear theory to protoplanetary disks subject to gravito-turbulence modeled as an effective viscosity, and cooling regulated by dust opacity. We find that viscosity renders the disk beyond ∼60 au dynamically unstable on radial lengthscales a few times the local disk thickness. This is coincident with the empirical condition for disk fragmentation based on a maximum sustainable stress. We suggest turbulent stresses can play an active role in realistic disk fragmentation by removing rotational stabilization against self-gravity, and that the observed transition in behavior from gravito-turbulent to fragmenting may reflect instability of the gravito-turbulent state itself.