GRMHD simulations of accretion onto Sgr A*: How important are radiative losses?
GRMHD simulations of accretion onto Sgr A*: How important are radiative losses?
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DOI：
10.1111/j.1365-2966.2012.21857.x
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发表时间：
2012-06
期刊：
影响因子：
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通讯作者：
S. Dibi;S. Drappeau;P. C. Fragile;S. Markoff;J. Dexter
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文献类型：
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作者：
S. Dibi;S. Drappeau;P. C. Fragile;S. Markoff;J. Dexter
我们提出了广义相对论磁流体动力学（GRMHD）的吸积流周围的超大质量黑洞在银河系中心，人马座A*（Sgr A*）的数值模拟。模拟包括第一次辐射冷却过程（同步，韧致辐射，逆康普顿）自洽的动力学，使我们能够测试忽略所有冷却损失的建模中的Sgr A* 的常见简化。我们确认，对于Sgr A*，如果银河系中心的吸积速度低于~10^{-8} Msun/yr，即Mdot < 10^{-7} Mdot_Edd，则忽略冷却损失是合理的近似。但在此极限以上，我们表明，辐射损失应考虑到显着差异出现在动力学和由此产生的光谱时，比较模拟与不冷却。这个极限意味着大多数附近的低光度活动星系核都处于应该考虑冷却的区域。我们进一步对银河系中心超大质量黑洞周围的轴对称气体吸积进行了参数研究。这种方法使我们能够调查一般的气体吸积的物理学，同时面对我们的结果与良好的研究和观察源，Sgr A*，作为一个测试案例。我们确认，吸积流和外流的性质是强烈依赖于磁场的初始几何形状。例如，我们发现，即使有非常高的自旋，也很难从带有多个单独的极向场环的圆盘中产生强大的外流。
We present general relativistic magnetohydrodynamic (GRMHD) numerical simulations of the accretion flow around the supermassive black hole in the Galactic centre, Sagittarius A* (Sgr A*). The simulations include for the first time radiative cooling processes (synchrotron, bremsstrahlung, and inverse Compton) self-consistently in the dynamics, allowing us to test the common simplification of ignoring all cooling losses in the modeling of Sgr A*. We confirm that for Sgr A*, neglecting the cooling losses is a reasonable approximation if the Galactic centre is accreting below ~10^{-8} Msun/yr i.e. Mdot < 10^{-7} Mdot_Edd. But above this limit, we show that radiative losses should be taken into account as significant differences appear in the dynamics and the resulting spectra when comparing simulations with and without cooling. This limit implies that most nearby low-luminosity active galactic nuclei are in the regime where cooling should be taken into account. We further make a parameter study of axisymmetric gas accretion around the supermassive black hole at the Galactic centre. This approach allows us to investigate the physics of gas accretion in general, while confronting our results with the well studied and observed source, Sgr A*, as a test case. We confirm that the nature of the accretion flow and outflow is strongly dependent on the initial geometry of the magnetic field. For example, we find it difficult, even with very high spins, to generate powerful outflows from discs threaded with multiple, separate poloidal field loops.