Angular Momentum Transport in Accretion Disks: Scaling Laws in MRI-driven Turbulence
Angular Momentum Transport in Accretion Disks: Scaling Laws in MRI-driven Turbulence
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DOI：
10.1086/522585
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发表时间：
2007-05
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影响因子：
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通讯作者：
M. Pessah;Chi-kwan Chan;D. Psaltis
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文献类型：
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作者：
M. Pessah;Chi-kwan Chan;D. Psaltis
我们提出了一个标度定律，预测了在非分层剪切箱中饱和核磁共振驱动湍流的数值模拟中获得的应力值。它将湍流应力与垂直磁场强度、声速、盒子的垂直尺寸和数值分辨率联系起来，并准确地预测了在各种物理条件下进行的35次数值模拟的结果。我们用我们的结果表明，在零净磁通量的模拟中，饱和应力与数值分辨率呈线性关系，如果将分辨率设置为等于天体物理盘的自然耗散尺度，则饱和应力可以忽略不计。我们得出结论，为了使mri驱动的湍流角动量输运能够解释观测推断的有效α粘度的大值，磁盘必须被一个显著的垂直磁场所缠绕，并且湍流磁能必须与热能接近等分。这一结果对吸积盘的光谱及其稳定性具有重要意义。
We present a scaling law that predicts the values of the stresses obtained in numerical simulations of saturated MRI-driven turbulence in nonstratified shearing boxes. It relates the turbulent stresses to the strength of the vertical magnetic field, the sound speed, the vertical size of the box, and the numerical resolution and predicts accurately the results of 35 numerical simulations performed for a wide variety of physical conditions. We use our result to show that the saturated stresses in simulations with zero net magnetic flux depend linearly on the numerical resolution and would become negligible if the resolution were set equal to the natural dissipation scale in astrophysical disks. We conclude that in order for MRI-driven turbulent angular momentum transport to be able to account for the large value of the effective alpha viscosity inferred observationally, the disk must be threaded by a significant vertical magnetic field and the turbulent magnetic energy must be in near equipartition with the thermal energy. This result has important implications for the spectra of accretion disks and their stability.