Unraveling Twisty Linear Polarization Morphologies in Black Hole Images
Unraveling Twisty Linear Polarization Morphologies in Black Hole Images
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DOI：
10.3847/1538-4357/acc8cd
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发表时间：
2022-10
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影响因子：
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通讯作者：
R. Emami;Angelo Ricarte;G. Wong;D. Palumbo;Dominic O. Chang;S. Doeleman;A. Broderick;R. Narayan;M. Wielgus;L. Blackburn;B. Prather;A. Chael;R. Anantua;K. Chatterjee;I. Martí-Vidal;J. Gómez;K. Akiyama;M. Liska;L. Hernquist;G. Tremblay;M. Vogelsberger;C. Alcock;Randall A. Smith;J. Steiner;P. Tiede;F. Roelofs
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作者：
R. Emami;Angelo Ricarte;G. Wong;D. Palumbo;Dominic O. Chang;S. Doeleman;A. Broderick;R. Narayan;M. Wielgus;L. Blackburn;B. Prather;A. Chael;R. Anantua;K. Chatterjee;I. Martí-Vidal;J. Gómez;K. Akiyama;M. Liska;L. Hernquist;G. Tremblay;M. Vogelsberger;C. Alcock;Randall A. Smith;J. Steiner;P. Tiede;F. Roelofs
我们调查广义相对论磁流体动力学模拟，以确定空间分辨黑洞图像中看到的线性极化的扭曲图案的物理起源，并解释其形态依赖于黑洞自旋。通过用一个简单的解析环模型表征所观察到的发射，我们发现扭曲的形态是由发射区的磁场结构决定的。此外，这种扭曲模式对自旋的依赖性可以归因于由于标架拖曳而发生的磁场几何形状的变化。通过研究解析环模型，我们发现多普勒增强和透镜效应的作用是次要的。法拉第旋转可能会导致系统的线性偏振模式的转变，但我们发现，它的影响是次主导的模型与强磁场和温和的离子-电子温度比。具有较弱磁场的模型受法拉第旋转的影响更大，并且具有比环形模型更复杂的发射几何形状。然而，这些模型目前不受最近M87* 的EHT观测的青睐。我们的研究结果表明，线性极化图可以提供一个探针的基础磁场结构周围的黑洞，这可能是有用的，然后间接推断黑洞自旋。这些结果的一般性应测试与替代代码，初始条件，等离子体物理处方。
We investigate general relativistic magnetohydrodynamic simulations to determine the physical origin of the twisty patterns of linear polarization seen in spatially resolved black hole images and explain their morphological dependence on black hole spin. By characterizing the observed emission with a simple analytic ring model, we find that the twisty morphology is determined by the magnetic field structure in the emitting region. Moreover, the dependence of this twisty pattern on spin can be attributed to changes in the magnetic field geometry that occur due to the frame dragging. By studying an analytic ring model, we find that the roles of Doppler boosting and lensing are subdominant. Faraday rotation may cause a systematic shift in the linear polarization pattern, but we find that its impact is subdominant for models with strong magnetic fields and modest ion-to-electron temperature ratios. Models with weaker magnetic fields are much more strongly affected by Faraday rotation and have more complicated emission geometries than can be captured by a ring model. However, these models are currently disfavoured by the recent EHT observations of M87*. Our results suggest that linear polarization maps can provide a probe of the underlying magnetic field structure around a black hole, which may then be usable to indirectly infer black hole spins. The generality of these results should be tested with alternative codes, initial conditions, and plasma physics prescriptions.