Global Radiation-Magnetohydrodynamic Simulations of Black-Hole Accretion Flow and Outflow: Unified Model of Three States
Global Radiation-Magnetohydrodynamic Simulations of Black-Hole Accretion Flow and Outflow: Unified Model of Three States
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DOI：
10.1093/pasj/61.3.l7
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发表时间：
2009-03
影响因子：
2.3
通讯作者：
K. Ohsuga;S. Mineshige;M. Mori;Y. Kato
中科院分区：
文献类型：
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作者：
K. Ohsuga;S. Mineshige;M. Mori;Y. Kato
已知黑洞吸积系统具有几种不同的模式（或谱态），例如低/硬态和高/软态。由于相应流的动力学是不同的，理论模型分别考虑每个状态。在这里，我们提出了一个统一的模型，我们的新的，全球性的，二维辐射磁流体动力学模拟的基础上。通过控制密度归一化，我们可以第一次用一个数值代码再现吸积流和外流的三种不同模式。当密度很大时（模型A），会形成一个几何上很厚的、非常明亮的圆盘，其中会发生光子捕获。当密度适中时（模型B），吸积气体可以通过发射辐射有效地冷却，从而产生薄盘，即，一种软态磁盘。当密度太低，辐射冷却变得不重要时（模型C），磁盘变得热，厚，暗淡;即，硬盘在模型A、B和C中，磁盘内的磁能分别被放大到气体能量的大约两倍、30%和20%。值得注意的是，盘流出的螺旋磁场，这是由辐射压力或磁压力的驱动力，是无处不在的任何吸积模式。最后，我们的模拟是一致的现象学的粘性处方，即磁盘的粘度是成比例的压力。
Black-hole accretion systems are known to possess several distinct modes (or spectral states), such as low/hard state and high/soft state. Since the dynamics of the corresponding flows is distinct, theoretical models were separately considered for each state. We here propose a unified model based on our new, global, two-dimensional radiation-magnetohydrodynamic simulations. By controlling a density normalization we could for the first time reproduce three distinct modes of accretion flow and outflow with one numerical code. When the density is large (model A), a geometrically thick, very luminous disk forms, in which photon trapping takes place. When the density is moderate (model B), the accreting gas can effectively be cooled by emitting radiation, thus generating a thin disk, i.e., a soft-state disk. When the density is too low for radiative cooling to be important (model C), a disk becomes hot, thick, and faint; i.e., a hard-state disk. The magnetic energy is amplified within the disk up to about twice, 30%, and 20% of the gas energy in models A, B, and C, respectively. Notably, the disk outflows with helical magnetic fields, which are driven either by radiation-pressure force or magnetic-pressure force, are ubiquitous in any accretion modes. Finally, our simulations are consistent with the phenomenological ˛-viscosity prescription; that is, the disk viscosity is proportional to the pressure.