Measuring Photon Rings with the ngEHT
Measuring Photon Rings with the ngEHT
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DOI：
10.3390/galaxies10060111
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发表时间：
2022-10
期刊：
影响因子：
2.5
通讯作者：
P. Tiede;Michael D. Johnson;D. Pesce;D. Palumbo;Dominic O. Chang;P. Galison
中科院分区：
文献类型：
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作者：
P. Tiede;Michael D. Johnson;D. Pesce;D. Palumbo;Dominic O. Chang;P. Galison
广义相对论预测，黑洞周围光学薄吸积流的图像通常应该有一个“光子环”，由一系列越来越尖锐的子环组成，这些子环对应于黑洞附近越来越强的透镜发射。由于透镜效应是由时空曲率决定的，因此光子环提供了精确测量黑洞特性和测试克尔度量的途径。我们探索了使用超长基线干涉仪（VLBI）与事件视界望远镜（EHT）和下一代EHT（ngEHT）来检测和测量光子环的前景。我们使用理想化自拟合对简单几何模型进行了一系列测试，结果表明 2017 年和 2022 年的 EHT 观测缺乏检测光子环的角分辨率和灵敏度，而 ngEHT 在 230 GHz 和 345 GHz 下改进的覆盖范围和角分辨率足以满足这些模型的需要。然后，我们通过应用“混合成像”，使用来自一般相对论磁流体动力学模拟的更真实的图像来分析探测前景，该混合成像同时对两个组件进行建模：灵活的光栅图像（用于捕获直接发射）和环形组件。使用贝叶斯 VLBI 建模包 Comrade.jl，我们表明，对于光子环检测和测量，混合成像的结果必须极其谨慎地解释 - 混合成像很容易对光子环产生误报，并且其环测量并不直接对应于光子环的属性。
General relativity predicts that images of optically thin accretion flows around black holes should generically have a “photon ring”, composed of a series of increasingly sharp subrings that correspond to increasingly strongly lensed emission near the black hole. Because the effects of lensing are determined by the spacetime curvature, the photon ring provides a pathway to precise measurements of the black hole properties and tests of the Kerr metric. We explore the prospects for detecting and measuring the photon ring using very long baseline interferometry (VLBI) with the Event Horizon Telescope (EHT) and the next-generation EHT (ngEHT). We present a series of tests using idealized self-fits to simple geometrical models and show that the EHT observations in 2017 and 2022 lack the angular resolution and sensitivity to detect the photon ring, while the improved coverage and angular resolution of ngEHT at 230 GHz and 345 GHz is sufficient for these models. We then analyze detection prospects using more realistic images from general relativistic magnetohydrodynamic simulations by applying “hybrid imaging”, which simultaneously models two components: a flexible raster image (to capture the direct emission) and a ring component. Using the Bayesian VLBI modeling package Comrade.jl, we show that the results of hybrid imaging must be interpreted with extreme caution for both photon ring detection and measurement—hybrid imaging readily produces false positives for a photon ring, and its ring measurements do not directly correspond to the properties of the photon ring.