DIRECT CALCULATION OF THE RADIATIVE EFFICIENCY OF AN ACCRETION DISK AROUND A BLACK HOLE
DIRECT CALCULATION OF THE RADIATIVE EFFICIENCY OF AN ACCRETION DISK AROUND A BLACK HOLE
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DOI：
10.1088/0004-637x/692/1/411
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发表时间：
2008-08
期刊：
影响因子：
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通讯作者：
S. Noble;J. Krolik;J. Hawley
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文献类型：
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作者：
S. Noble;J. Krolik;J. Hawley
磁流体湍流的数值模拟为详细研究吸积动力学提供了可能。然而，要将流入动力学(在很大程度上取决于角动量传输)与辐射(在很大程度上取决于热力学和光子扩散)联系起来，需要做出特别的努力。为此，我们将通量守恒的广义相对论MHD(GRMHD)码的危害从轴对称扩展到全三维。能量守恒算法的使用允许在相对论吸积过程中耗散的能量被捕获为热。包含一个简单的光学薄层冷却功能，允许显式控制模拟磁盘的几何厚度，以及直接计算与吸积应力相关的辐射冷却的幅度和位置。完全相对论光线追踪被用来计算远距离观察者接收到的光度。对于长宽比为H/r≃0.1的吸积在自旋参数a/M=0.9的黑洞上的圆盘，我们发现存在着比经典Novikov-Thorne模型所预言的更大的耗散.然而，其中很大一部分发生在势的深处，那里的光子捕获和引力红移可以强烈地限制逃逸到无穷大的净光子能量。此外，有了这些参数和这个辐射模型，大量的热能和磁能仍留在气体中，并被黑洞吸收。在我们的模型中，到达无穷远的净光度比Novikov-Thorne预测的大6%。如果吸积的热能被完全辐射，吸积流的总光度将比≃-Thorne值大20%。
Numerical simulation of magnetohydrodynamic (MHD) turbulence makes it possible to study accretion dynamics in detail. However, special effort is required to connect inflow dynamics (dependent largely on angular momentum transport) to radiation (dependent largely on thermodynamics and photon diffusion). To this end, we extend the flux-conservative, general relativistic MHD (GRMHD) code HARM from axisymmetry to full three dimensions. The use of an energy conserving algorithm allows the energy dissipated in the course of relativistic accretion to be captured as heat. The inclusion of a simple optically thin cooling function permits explicit control of the simulated disk's geometric thickness as well as a direct calculation of both the amplitude and location of the radiative cooling associated with the accretion stresses. Fully relativistic ray-tracing is used to compute the luminosity received by distant observers. For a disk with aspect ratio H/r ≃ 0.1 accreting onto a black hole with spin parameter a/M = 0.9, we find that there is significant dissipation beyond that predicted by the classical Novikov–Thorne model. However, much of it occurs deep in the potential, where photon capture and gravitational redshifting can strongly limit the net photon energy escaping to infinity. In addition, with these parameters and this radiation model, significant thermal and magnetic energy remains with the gas and is accreted by the black hole. In our model, the net luminosity reaching infinity is 6% greater than the Novikov–Thorne prediction. If the accreted thermal energy were wholly radiated, the total luminosity of the accretion flow would be ≃20% greater than the Novikov–Thorne value.