Shadow Geometry of Kerr Naked Singularities
Shadow Geometry of Kerr Naked Singularities
复制标题
DOI：
10.3847/1538-4357/ace697
复制
发表时间：
2023-02
期刊：
影响因子：
--
通讯作者：
Bao Nguyen;P. Christian;Chi-kwan Chan
中科院分区：
文献类型：
--
作者：
Bao Nguyen;P. Christian;Chi-kwan Chan
对超大质量黑洞(SMBH)以事件视界尺度的分辨率直接成像，就像最近由事件视界望远镜所做的那样，允许测试SMBH的替代模型，如克尔裸奇点(KNSS)。我们证明了KNS的阴影可以是闭合的、开放的或消失的，这取决于自转和观测倾角。我们研究了KNS阴影打开缺口的临界参数，这是黑洞阴影不会发生的独特现象。我们证明了在一定的倾角范围内，只有当无因次自转为≲1.18时，Kns阴影才能闭合，而当自转为≳1.18时，Kns阴影才会消失。我们进一步分析了光子轨道的有效角动量，以说明光测地线与KNS阴影几何之间的基本联系。我们还进行了数值广义相对论光线跟踪计算，再现了KNS阴影中的解析拓扑变化，并说明了由于缺少事件视界而导致的阴影内的其他观测特征。通过比较KNS阴影的几何特征和黑洞阴影观测，KNS阴影中的拓扑变化可以用来检验宇宙审查假说，KNS可以作为SMBHs的替代模型。
Direct imaging of supermassive black holes (SMBHs) at event horizon-scale resolutions, as recently done by the Event Horizon Telescope, allows for testing alternative models to SMBHs such as Kerr naked singularities (KNSs). We demonstrate that the KNS shadow can be closed, open, or vanishing, depending on the spins and observational inclination angles. We study the critical parameters where the KNS shadow opens a gap, a distinctive phenomenon that does not happen with the black hole shadow. We show that the KNS shadow can only be closed for dimensionless spin a ≲ 1.18 and vanishing for a ≳ 1.18 for certain ranges of inclination angles. We further analyze the effective angular momentum of photon orbits to demonstrate the fundamental connections between light geodesics and the KNS shadow geometry. We also perform numerical general relativistic ray-tracing calculations, which reproduce the analytical topological change in the KNS shadow, and illustrate other observational features within the shadow due to the lack of an event horizon. By comparing the geometric features of the KNS shadow with black hole shadow observations, the topological change in the shadow of KNSs can be used to test the cosmic censorship hypothesis and KNSs as alternative models to SMBHs.