We study optical phenomena related to appearance of Keplerian accretion discs orbiting Kerr superspinars predicted by the string theory. The superspinar exterior is described by the standard Kerr naked singularity geometry breaking the black hole limit on the internal angular momentum (spin). We construct local photon escape cones for a variety of orbiting sources that enable to determine the superspinars silhouette in the case of distant observers. We show that the superspinar silhouette depends strongly on the assumed edge where the external Kerr spacetime is joined to the internal spacetime governed by the string theory and significantly differs from the black hole silhouette. The appearance of the accretion disc is strongly dependent on the value of the superspinar spin in both their shape and frequency shift profile. Apparent extension of the disc grows significantly with growing spin, while the frequency shift grows with descending spin. This behavior differs substantially from appearance of discs orbiting black holes enabling thus, at least in principle, to distinguish clearly the Kerr superspinars and black holes. In vicinity of a Kerr superspinar the non-escaped photons have to be separated to those captured by the superspinar and those being trapped in its strong gravitational field leading to self-illumination of the disc that could even influence its structure and causes self-reflection effect of radiation of the disc. The amount of trapped photons grows with descending of the superspinar spin. We thus can expect significant self-illumination effects in the field of Kerr superspinars with near-extreme spin $a \sim 1$.
Light curves of the hot spots on circular orbits around generic regular black holes related to non-linear electrodynamics with Maxwellian weak-field Limit
银河系中心的S型恒星围绕着中心的超大质量黑洞运行，其速度只有光速的百分之几。GR引起的红移扰动通过两个不同的通道进入动力学。后牛顿体系扰动开普勒轨道（Zucker等人，2006，Kannan & Saha 2009），以及来自Minkowski的光子（Angelil & Saha 2010）。在v^2量级包含引力时间膨胀，标志着红移第一次偏离视线速度。首阶史瓦西项曲线空间，并在阶v^3处进入。经典开普勒现象主导了总红移。足够分辨率的光谱测量将允许检测这些后牛顿效应。我们估计所需的光谱分辨率来检测这些影响通过拟合红移曲线通过五个开普勒元素加上黑洞质量模拟数据。我们使用一个夸张的S2轨道--其半长轴是真实S2的一小部分。这放大了相对论效应，并允许相对论术语之间的清晰视觉区分。我们认为，色散约为10 km/s的S2光谱数据可以清晰地检测引力红移，而色散约为1 km/s的S2光谱数据足以检测首阶空间曲率。
Autocorrelation in black hole flare movies: Departures from Kerr
Institute of Fundamental Physics and Quantum Technology, and School of Physical Science and Technology, Ningbo University（宁波大学基础物理与量子技术研究所和物理科学与技术学院）；Zhejiang Key Laboratory of Extreme Universe, and BINGO Center, Ningbo University（宁波大学浙江极端宇宙重点实验室和BINGO中心）；School of Physics, and Center for High Energy Physics, Peking University（北京大学物理学院和高能物理研究中心）
