Collaborative Research: Experimental General Relativity using Radio Interferometry of a Black Hole Photon Ring

2019年4月，事件视界望远镜（EHT）合作发布了黑洞的第一张图像，这一突破性的结果引发了一系列新的理论研究。这些发现揭示了黑洞图像带有独特的相对论特征，这些特征嵌入在围绕黑洞的明亮狭窄的环中。史密森学会天体物理天文台和范德比尔特大学之间的一项研究合作将探索这种“光子环”的基本性质，将展示如何使用无线电干涉测量法对其进行研究，并将确定可以通过观测进行探测的黑洞时空的性质。 这些研究人员已经将光子环建立为广义相对论的普遍预测：它是由黑洞事件视界附近的光线极端弯曲引起的独立于物质的效应。事实上，爱因斯坦的理论预测克尔黑洞可以使光线偏转到这样的程度，即它们在最终到达遥远的观察者之前绕着黑洞旋转-可能几次。 黑洞成像是一个新兴的领域，已经在全球范围内普及，公众参与度很高。 作为该项目的一部分，研究人员将通过为神经多样性和特殊教育学生开发新的课堂活动以及新颖的艺术展览来吸引公众参与这项研究，这些展览传达了隐藏在黑洞图像中的优雅和神秘。在这个项目中，科学家们将研究轨道光编码的关于黑洞时空几何的信息，以及周围等离子体和电磁场的天体物理条件。这将联合收割机结合两条平行但又相互关联的工作线：1）在理论方面，对简单模型的分析将建立直觉并提供对光子环的干涉特性的洞察，而发展依赖于时间的、具有等离子体天体物理学所告知的可变性的“慢光”光子环模型将澄清简单模型如何与现实吸积流模型中的复杂结构相关联; 2）在观测方面，逐步发展更精细的统计推断工具和数值模拟将利用这些模型从干涉测量数据中提取越来越精确的超大质量黑洞天体物理学知识，最终形成质量，自旋，M87* 和Sgr A* 的倾角该项目的两个主要研究成果将是对独特的光子环特征的全面表征，VLBI（甚长基线干涉测量），以及使用当前EHT数据对M87* 和Sgr A* 的质量、自旋和倾角的模型不可知估计。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

In April 2019, the Event Horizon Telescope (EHT) collaboration released the first images of a black hole, a breakthrough result that has since prompted a flurry of new theoretical studies. These have revealed that black hole images carry distinctive relativistic signatures, which are embedded within a bright, narrow ring encircling the black hole. A research collaboration between the Smithsonian Institution Astrophysical Observatory and Vanderbilt University will explore the fundamental properties of this “photon ring,” will show how it can be studied using radio interferometry, and will determine the properties of a black hole’s spacetime that can be probed with observations. These researchers have already established the photon ring as a universal prediction of General Relativity: it is a matter-independent effect caused by the extreme bending of light near the event horizon of the black hole. Indeed, Einstein’s theory predicts that Kerr black holes can deflect light rays to such a degree that they circumnavigate the black hole—possibly several times—before eventually reaching distant observers. Black hole imaging is a nascent field with an already global reach and intense public engagement. As part of this project, the investigators will engage the public with this research through the development of new classroom activities for neurodiverse and special education students as well as novel art exhibits conveying the elegance and mysteries hidden within black hole images.During this project, scientists will study the information that the orbiting light encodes about the geometry of the black hole’s spacetime, as well as the astrophysical conditions of the surrounding plasma and electromagnetic fields. This will combine the pursuit of two parallel yet interconnected lines of work: 1) On the theory side, analysis of simple models will build intuition and provide insight into interferometric properties of the photon ring, while development of time- dependent, “slow-light” photon ring models with variability informed by plasma astrophysics will clarify how the simple models relate to the complex structure in a realistic accretion flow model; and 2) On the observational side, the development of progressively more elaborate statistical inference tools and numerical simulations will utilize these models to extract increasingly precise knowledge of supermassive black hole astrophysics from interferometric data, culminating in formal posteriors for the mass, spin, and inclination of both M87* and Sgr A* from EHT data.Two major research outputs of this project will be the comprehensive characterization of the unique photon ring signatures that can be targeted with VLBI (very-long-baseline interferometry), and model-agnostic estimates of mass, spin, and inclination for M87* and Sgr A* using current EHT data.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.