SATURATION OF THE MAGNETO-ROTATIONAL INSTABILITY IN STRONGLY RADIATION-DOMINATED ACCRETION DISKS
SATURATION OF THE MAGNETO-ROTATIONAL INSTABILITY IN STRONGLY RADIATION-DOMINATED ACCRETION DISKS
复制标题
强辐射主导的吸积盘中磁旋转不稳定性的饱和
DOI：
10.1088/0004-637x/767/2/148
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
S. Davis
中科院分区：
文献类型：
--
作者：
Yan;J. Stone;S. Davis
在非分层剪切盒近似下，用一种新的Godunov辐射MHD程序研究了强辐射主导吸积盘中磁旋转不稳定性(MRI)的饱和能级.由于垂直重力在这项工作中被忽略，我们的重点放在MRI如何在盘的光学厚度的中面饱和。我们证实了核磁共振产生的湍流在辐射为主的区域是非常可压缩的，正如先前使用通量限制扩散近似计算所发现的那样。我们还发现，在使用更大的水平区域(径向最大为垂直标度高度的四倍)的计算中，饱和度性质几乎没有区别。然而，在强辐射压力主导的圆盘中(辐射能量密度达到气体剩余质量能量密度的∼1%)，我们发现磁共振湍流产生的麦克斯韦应力大于相同气体压力替代辐射压力时产生的麦克斯韦应力。同时，麦克斯韦应力与雷诺应力之比比气体压强占主导的情况提高了近8倍。我们认为这一效应是由辐射阻力引起的，辐射阻力的作用类似于体粘性，改变了流体的有效磁普朗特数。辐射粘度显著超过微观等离子体粘度和电阻率，确保辐射主导的系统占据高磁普朗特数区域。然而，我们发现，与流动中的麦克斯韦应力和雷诺应力相比，辐射剪切粘度可以忽略不计。这可能对辐射为主的吸积盘的结构有重要的影响。
The saturation level of the magneto-rotational instability (MRI) in a strongly radiation-dominated accretion disk is studied using a new Godunov radiation MHD code in the unstratified shearing box approximation. Since vertical gravity is neglected in this work, our focus is on how the MRI saturates in the optically thick mid-plane of the disk. We confirm that turbulence generated by the MRI is very compressible in the radiation-dominated regime, as found by previous calculations using the flux-limited diffusion approximation. We also find little difference in the saturation properties in calculations that use a larger horizontal domain (up to four times the vertical scale height in the radial direction). However, in strongly radiation pressure dominated disks (one in which the radiation energy density reaches ∼1% of the rest mass energy density of the gas), we find that Maxwell stress from the MRI turbulence is larger than the value produced when radiation pressure is replaced with the same amount of gas pressure. At the same time, the ratio between Maxwell stress and Reynolds stress is increased by almost a factor of eight compared with the gas pressure dominated case. We suggest that this effect is caused by radiation drag, which acts like bulk viscosity and changes the effective magnetic Prandtl number of the fluid. Radiation viscosity significantly exceeds both the microscopic plasma viscosity and resistivity, ensuring that radiation-dominated systems occupy the high magnetic Prandtl number regime. Nevertheless, we find that radiative shear viscosity is negligible compared to the Maxwell stress and Reynolds stress in the flow. This may have important implications for the structure of radiation-dominated accretion disks.