Brightness Asymmetry of Black Hole Images as a Probe of Observer Inclination
Brightness Asymmetry of Black Hole Images as a Probe of Observer Inclination
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DOI：
10.3847/1538-4357/ac33a7
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发表时间：
2021-05
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影响因子：
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通讯作者：
L. Medeiros;Chi-kwan Chan;R. Narayan;F. Özel;D. Psaltis
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作者：
L. Medeiros;Chi-kwan Chan;R. Narayan;F. Özel;D. Psaltis
事件视界望远镜最近捕捉到了M87星系中心超大质量黑洞的图像，该图像显示了一个环状发射结构，南侧仅比北侧略亮。这种相对弱的亮度分布沿着环的不对称性被解释为观测者的低倾角（M87约为17°）的结果，这抑制了多普勒波束和增强效应，否则可能会由于轨道等离子体的近相对论速度而预期。在这项工作中，我们使用了一个大套件的广义相对论磁流体动力学模拟重新评估这一论点的有效性。通过构造明确的反例，我们表明，低倾角是一个充分的，但不是必要的条件，图像具有低亮度不对称性。吸积流模型具有接近黑洞视界的高累积磁通量（所谓的磁制动盘）和低黑洞自旋，其角速度大大小于相同位置处测试粒子的轨道速度。因此，这种模型可以产生具有低亮度不对称性的图像，即使在边缘上观看时也是如此。
The Event Horizon Telescope recently captured images of the supermassive black hole in the center of the M87 galaxy, which shows a ring-like emission structure with the south side only slightly brighter than the north side. This relatively weak asymmetry in the brightness profile along the ring has been interpreted as a consequence of the low inclination of the observer (around 17° for M87), which suppresses the Doppler beaming and boosting effects that might otherwise be expected due to the nearly relativistic velocities of the orbiting plasma. In this work, we use a large suite of general relativistic magnetohydrodynamic simulations to reassess the validity of this argument. By constructing explicit counterexamples, we show that low inclination is a sufficient but not necessary condition for images to have low brightness asymmetry. Accretion flow models with high accumulated magnetic flux close to the black hole horizon (the so-called magnetically arrested disks) and low black hole spins have angular velocities that are substantially smaller than the orbital velocities of test particles at the same location. As a result, such models can produce images with low brightness asymmetry even when viewed edge on.