The Variability of the Black Hole Image in M87 at the Dynamical Timescale
The Variability of the Black Hole Image in M87 at the Dynamical Timescale
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DOI：
10.3847/1538-4357/ac332e
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发表时间：
2021-11
期刊：
影响因子：
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通讯作者：
K. Satapathy;D. Psaltis;F. Özel;L. Medeiros;Sean T. Dougall;Chi-kwan Chan;M. Wielgus;B. Prather-B.-Prath
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作者：
K. Satapathy;D. Psaltis;F. Özel;L. Medeiros;Sean T. Dougall;Chi-kwan Chan;M. Wielgus;B. Prather-B.-Prath
用事件视界望远镜（EHT）获得的黑洞图像在其视界附近的动力学时间尺度上是可变的。对于M87星系中心的黑洞，这个时间尺度（5-61天）与2017年EHT观测的6天范围相当。闭合相位沿着基线三角形是稳健的干涉观测量，其对图像的预期结构变化敏感，但不受基于站的大气和仪器误差的影响。我们探索了在2017年观测中形成的所有六个线性独立的非平凡基线三角形上的闭合相测量值的日常变化。我们发现，三个三角形显示出非常低的日间变异性，离散度为0.3 °-5°。唯一表现出显著更高可变性（Δ 90°-180°）的三角形是那些基线穿过u-v平面上可见度振幅最小值的三角形，正如理论建模所预期的那样。我们使用了两套广义相对论磁流体动力学模拟来探索预测的变化对各种黑洞和吸积流参数的依赖性。我们发现，改变磁场配置，电子温度模型，或黑洞自旋有一个边际效应的模型与观测水平的变化一致性。另一方面，模型最具鉴别力的图像特征是发射亮环的分数宽度。最好地再现所观察到的小水平的可变性的模型的特点是薄的环状图像的结构占主导地位的引力透镜效应，从而最少受湍流的吸积等离子体。
The black hole images obtained with the Event Horizon Telescope (EHT) are expected to be variable at the dynamical timescale near their horizons. For the black hole at the center of the M87 galaxy, this timescale (5–61 days) is comparable to the 6 day extent of the 2017 EHT observations. Closure phases along baseline triangles are robust interferometric observables that are sensitive to the expected structural changes of the images but are free of station-based atmospheric and instrumental errors. We explored the day-to-day variability in closure-phase measurements on all six linearly independent nontrivial baseline triangles that can be formed from the 2017 observations. We showed that three triangles exhibit very low day-to-day variability, with a dispersion of ∼3°–5°. The only triangles that exhibit substantially higher variability (∼90°–180°) are the ones with baselines that cross the visibility amplitude minima on the u–v plane, as expected from theoretical modeling. We used two sets of general relativistic magnetohydrodynamic simulations to explore the dependence of the predicted variability on various black hole and accretion-flow parameters. We found that changing the magnetic field configuration, electron temperature model, or black hole spin has a marginal effect on the model consistency with the observed level of variability. On the other hand, the most discriminating image characteristic of models is the fractional width of the bright ring of emission. Models that best reproduce the observed small level of variability are characterized by thin ring-like images with structures dominated by gravitational lensing effects and thus least affected by turbulence in the accreting plasmas.