Global Radiation Magnetohydrodynamic Simulations of sub-Eddington Accretion Disks around Supermassive Black Holes
Global Radiation Magnetohydrodynamic Simulations of sub-Eddington Accretion Disks around Supermassive Black Holes
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DOI：
10.3847/1538-4357/ab4a00
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发表时间：
2019-11-10
影响因子：
4.9
通讯作者：
Davis, Shane W.
中科院分区：
文献类型：
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作者：
Jiang, Yan-Fei;Blaes, Omer;Davis, Shane W.
我们进行了全球三维辐射磁流体动力学模拟的内部区域的吸积流周围的5 xfffd; x5 e0;10（8）M黑洞，质量吸积率达到7%和20%的爱丁顿值。我们选择的初始字段拓扑结构，导致内磁盘支持磁压力，表面密度显着小于标准薄磁盘模型预测的值，以及更大的磁盘规模的高度。在许多热时间尺度上，磁盘没有显示出任何热不稳定性的迹象。在吸积率较低的情况下，一半以上的吸积是由光学薄的日冕区域的辐射粘性驱动的，而在盘的光学厚的部分的吸积是由磁旋转不稳定性引起的湍流的麦克斯韦和雷诺应力驱动的。具有气体温度的光学薄等离子体？10（8）K在两种模拟中都只在引力半径内10个区域产生，并且在吸积率较高的情况下更致密。这种等离子体不会在较大的半径处形成，因为表面密度随着半径向外增加，导致光球层外的耗散较少。与标准的薄盘模型相比，在我们的模拟中，表面密度随着每个半径处质量吸积速率的增加而增加。这导致了一个相对较弱的热等离子体成分的模拟具有较高的吸积率。我们认为，这些结果可能提供了一个物理机制，了解一些观测到的日冕和光谱的活动星系核的性质。
We conduct global three-dimensional radiation magnetohydrodynamic simulations of the inner regions of accretion flows around a 5 & xfffd;& x5e0;10(8)M black hole, with mass accretion rates reaching 7% and 20% of the Eddington value. We choose initial field topologies that result in an inner disk supported by magnetic pressure, with surface density significantly smaller than the values predicted by the standard thin-disk model as well as a much larger disk scale height. The disks do not show any sign of thermal instability over many thermal timescales. More than half of the accretion is driven by radiation viscosity in the optically thin coronal region for the case of the lower accretion rate, while accretion in the optically thick part of the disk is driven by the Maxwell and Reynolds stresses from turbulence caused by magnetorotational instability. Optically thin plasma with gas temperatures ?10(8) K is generated only in the inner 10 gravitational radii in both simulations, and is more compact in the case of the higher accretion rate. Such plasma does not form at larger radii because the surface density increases outward with radius, causing less dissipation outside the photosphere. In contrast to standard thin-disk models, the surface density in our simulations increases with increasing mass accretion rate at each radius. This causes a relatively weaker hot plasma component for the simulation with a higher accretion rate. We suggest that these results may provide a physical mechanism for understanding some of the observed properties of coronae and spectra of active galactic nuclei.