A coordinate-independent characterization of a black hole shadow
A coordinate-independent characterization of a black hole shadow
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DOI：
10.1093/mnras/stv2079
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发表时间：
2015-03
影响因子：
4.8
通讯作者：
A. Abdujabbarov;L. Rezzolla;B. Ahmedov
中科院分区：
文献类型：
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作者：
A. Abdujabbarov;L. Rezzolla;B. Ahmedov
目前正在进行一项大规模的国际努力，以评估银河系中心人马座A*（Sgr A*）致密源的无线电发射中是否存在阴影。如果被探测到，这个阴影将提供黑洞存在的第一个直接证据，并证明Sgr A* 是一个超大质量黑洞。此外，阴影的形状可以用来了解事件视界附近的极端引力，并确定哪种引力理论更好地描述了观测结果。到目前为止，阴影的数学描述使用了许多简化的假设，这些假设不太可能被真实的观测数据所满足。在这里，我们提供了一个一般的形式主义来描述的阴影作为一个任意的极曲线表示的勒让德展开。我们的形式主义不假定任何知识的属性的阴影，例如，其中心的位置，并提供了一些路线来表征扭曲的曲线相对于参考圆。这些扭曲可以通过分析相同数据的不同团队以独立于坐标的方式实现。我们表明，新的形式主义提供了一个准确和强大的描述嘈杂的观测数据，与以前的方法相比，失真的测量具有较小的误差方差。
A large international effort is under way to assess the presence of a shadow in the radio emission from the compact source at the centre of our Galaxy, Sagittarius A* (Sgr A*). If detected, this shadow would provide the first direct evidence of the existence of black holes and that Sgr A* is a supermassive black hole. In addition, the shape of the shadow could be used to learn about extreme gravity near the event horizon and to determine which theory of gravity better describes the observations. The mathematical description of the shadow has so far used a number of simplifying assumptions that are unlikely to be met by the real observational data. We here provide a general formalism to describe the shadow as an arbitrary polar curve expressed in terms of a Legendre expansion. Our formalism does not presume any knowledge of the properties of the shadow, e.g. the location of its centre, and offers a number of routes to characterize the distortions of the curve with respect to reference circles. These distortions can be implemented in a coordinate-independent manner by different teams analysing the same data. We show that the new formalism provides an accurate and robust description of noisy observational data, with smaller error variances when compared to previous approaches for the measurement of the distortion.