Global Structures of Optically Thin Black Hole Accretion Flows Obtained from Direct Magnetohydrodynamic Simulations
Global Structures of Optically Thin Black Hole Accretion Flows Obtained from Direct Magnetohydrodynamic Simulations
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DOI：
10.1093/pasj/56.4.671
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发表时间：
2004-08
影响因子：
2.3
通讯作者：
M. Machida;K. Nakamura;R. Matsumoto
中科院分区：
文献类型：
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作者：
M. Machida;K. Nakamura;R. Matsumoto
利用三维磁流体动力学模拟研究了辐射低效黑洞吸积流的整体结构。初始状态是一个恒定的角动量环面弱环向磁场穿过。环面被假定为嵌入在一个低密度，球形，等温晕。我们发现，在由环面吸积形成的光学薄热盘的最内部区域（< 15 rg：rg是史瓦西半径），径向结构可以用一维定常跨音速ADAF（平流主导吸积流）解来描述，该解考虑了α的径向依赖性。数值结果表明，从磁盘出现的磁通量创建一个磁激活层中的磁重联产生流出沿着磁场线。我们还研究了盘结构对初始环面外压的依赖性。外压越大，磁场放大的饱和程度越高。因此，外部压力增强了磁盘的磁活动。当外压为环面最大压力的5-20%时，流出的动能和坡印廷能流约为通过吸积平流到黑洞的能流的1%。
We studied the global structures of radiatively inefficient black hole accretion flows by three-dimensional magnetohydrodynamic simulations. The initial state is a constant angular-momentum torus threaded by weak toroidal magnetic fields. The torus is assumed to be embedded in a low-density, spherical, isothermal halo. We found that in the innermost region ( �< 15 rg: rg is the Schwarzschild radius) of optically thin hot disks formed by accretion from the torus, the radial structure can be described by a one-dimensional steady transonic ADAF (Advection Dominated Accretion Flow) solution that takes into account the radial dependence of α. Numerical results indicate that the magnetic flux emerging from the disk creates a magnetically active layer in which magnetic reconnection generates outflows along magnetic field lines. We also studied the dependence of the disk structure on the external pressure of the initial torus. The saturation level of magnetic field amplification is higher for a model with a larger external pressure. Thus, external pressure enhances the magnetic activity of the disk. When the external pressure is 5–20% of the maximum pressure of the torus, the kinetic and Poynting energy flux of the outflow is about 1% of the energy flux advected to the black hole through accretion.