Two-dimensional Radiation-Hydrodynamic Model for Limit-Cycle Oscillations of Luminous Accretion Disks
Two-dimensional Radiation-Hydrodynamic Model for Limit-Cycle Oscillations of Luminous Accretion Disks
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DOI：
10.1086/500184
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发表时间：
2005-12
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影响因子：
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通讯作者：
K. Ohsuga
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文献类型：
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作者：
K. Ohsuga
通过二维辐射流体动力学模拟研究了黑洞周围发光吸积盘的时间演化。粘度采用α配方。假定粘性应力张量的径向-方位分量与光学厚区的总压力和光学薄区的气体压力成正比。粘度参数α取为0.1.我们发现了发光度在高、低态之间的极限环变化。当我们将外盘边界的质量输入率设置为100LE/c2时，光度突然从0.3LE增加到2LE，其中LE是爱丁顿光度。我们的数值结果可以解释在微类星体GRS1915+105中观测到的周期性爆发的变化、幅度和持续时间。结果表明，多维效应在高光度态中起着重要作用。在这种状态下，外流是由强辐射力驱动的，由于光子捕获效应，盘内耗散的辐射能量的一部分被黑洞吞噬。这种捕获的光度与圆盘的光度相当。我们还计算了另外两种情况：一种是吸积率远大于不稳定性的临界值，另一种是粘性应力张量只与气体压力成正比，即使辐射压力占主导地位。在这些情况下，我们没有发现准周期光变化。这证实了在模拟中发现的极限环行为是由圆盘不稳定性引起的。
We investigate the time evolution of luminous accretion disks around black holes by conducting two-dimensional radiation-hydrodynamic simulations. We adopt the α prescription for the viscosity. The radial-azimuthal component of the viscous stress tensor is assumed to be proportional to the total pressure in the optically thick region and the gas pressure in the optically thin regime. The viscosity parameter, α, is taken to be 0.1. We find the limit-cycle variation in luminosity between high and low states. When we set the mass input rate from the outer disk boundary to be 100LE/c2, the luminosity suddenly rises from 0.3LE to 2LE, where LE is the Eddington luminosity. It decays after retaining the high value for about 40 s. Our numerical results can explain the variability amplitude and duration of the recurrent outbursts observed in microquasar GRS 1915+105. We show that multidimensional effects play an important role in the high-luminosity state. In this state, the outflow is driven by the strong radiation force, and some part of the radiation energy dissipated inside the disk is swallowed by the black hole due to the photon-trapping effects. This trapped luminosity is comparable to the disk luminosity. We also calculate two more cases: one with a much larger accretion rate than the critical value for the instability and the other with the viscous stress tensor being proportional to the gas pressure only, even when the radiation pressure is dominant. We find no quasi-periodic light variations in these cases. This confirms that the limit-cycle behavior found in the simulations is caused by the disk instability.