BLACK HOLE SPIN AND THE RADIO LOUD/QUIET DICHOTOMY OF ACTIVE GALACTIC NUCLEI
BLACK HOLE SPIN AND THE RADIO LOUD/QUIET DICHOTOMY OF ACTIVE GALACTIC NUCLEI
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DOI：
10.1088/0004-637x/711/1/50
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发表时间：
2009-11
期刊：
影响因子：
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通讯作者：
A. Tchekhovskoy;R. Narayan;J. McKinney
中科院分区：
文献类型：
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作者：
A. Tchekhovskoy;R. Narayan;J. McKinney
在射电波段，射电强活动星系核（AGN）的亮度平均是射电静活动星系核的1000倍。我们调查这种无线电大声/安静的二分法是否可以是由于不同的旋转的中央黑洞（BH）的权力无线电发射喷气机。使用广义相对论磁流体动力学模拟，我们构建了稳态轴对称的数值模型的范围广泛的BH自旋（无量纲自旋参数0.1 <$a0.9999）和各种喷流的几何形状。我们假设通过半径为rH（a）的BH视界的总磁通量保持不变。如果黑洞被一个薄的吸积盘包围，我们发现黑洞的总功率输出近似地与黑洞的角频率P <$Ω 2 H <$（a/rH）2成二次方关系。我们的结论是，在这种情况下，BH自旋的差异可以产生的功率变化最多只有几十。然而，如果圆盘很厚，使得喷流对着极轴周围的一个窄立体角，那么功率依赖性变得更陡，P <$Ω 4 H甚至<$Ω 6 H。对于真实的BH自旋分布，1000的功率变化是可能的。我们推导出一个解析解，精确地再现了射流功率与ΩH的陡峭标度，我们提供了一个数值拟合公式，再现了我们所有的模拟结果。我们讨论了其他物理效应，可能有助于观察到的无线电大声/安静的AGN二分法。
Radio loud active galactic nuclei (AGNs) are on average 1000 times brighter in the radio band compared to radio quiet AGNs. We investigate whether this radio loud/quiet dichotomy can be due to differences in the spin of the central black holes (BHs) that power the radio-emitting jets. Using general relativistic magnetohydrodynamic simulations, we construct steady state axisymmetric numerical models for a wide range of BH spins (dimensionless spin parameter 0.1 ⩽ a ⩽ 0.9999) and a variety of jet geometries. We assume that the total magnetic flux through the BH horizon at radius rH(a) is held constant. If the BH is surrounded by a thin accretion disk, we find that the total BH power output depends approximately quadratically on the angular frequency of the hole, P ∝ Ω2H ∝ (a/rH)2. We conclude that, in this scenario, differences in the BH spin can produce power variations of only a few tens at most. However, if the disk is thick such that the jet subtends a narrow solid angle around the polar axis, then the power dependence becomes much steeper, P ∝ Ω4H or even ∝Ω6H. Power variations of 1000 are then possible for realistic BH spin distributions. We derive an analytic solution that accurately reproduces the steeper scaling of jet power with ΩH and we provide a numerical fitting formula that reproduces all our simulation results. We discuss other physical effects that might contribute to the observed radio loud/quiet dichotomy of AGNs.