Clumps of material orbiting a black hole may be disturbed, somewhat like comets in the Kuiper belt, to relatively small periastron orbits. Each periastron passage changes the orbital parameters in such a way that the orbit becomes more and more eccentric and the angular momentum approaches the critical value for tidal capture. When this value is reached, the body is suddenly caught by the relativistic potential to the last periastron (occurring at two Schwarzschild radii for a non rotating black hole). In this process the transfer of orbital into internal energy heats the body before it makes a few more turns toward the horizon of the black hole. Because of strong relativistic effects this last bright message from the object is seen as a quasi-periodic flare. Assuming that a black hole may be fed by a large number of such small debris we calculate light curves expected from such events. We investigate the resemblance of the Fourier spectra of such light curves with those of observed QPOs.
Epicyclic oscillations in spinning particle motion around Kerr black hole applied in models fitting the quasi-periodic oscillations observed in quasars and microquasars
Evolution of the extended X-ray emission from the PSR B1259-63/LS 2883 binary in the 2014-2017 binary cycle
我们利用钱德拉X射线天文台对一颗周期为1236.7天的年轻脉冲星（PSR B 1259 -63）--大质量Be星--的γ射线双星LS 2883进行了一系列观测。该系统在2014年5月4日经过近星点后的352至1175天内被观测到。观测结果证实了高速喷出物的周期性，这些喷出物表现为远离双星的扩展X射线结构（团块）。与之前的监测活动（2010年至2014年的近星点通过）的结果相比，这一次我们发现的证据表明，该团块被加速到预计的速度$ v_{\perp}\approx0.15c$，加速度为$a_{\perp}=47\pm2$ cm s $^{-2}$（均匀加速运动），假设它是在近星点通过附近发射的。观察到的X射线性质的团块是一致的同步辐射从脉冲星风粒子加速在脉冲星风和团块之间的界面。我们还用{ \sl Hubble Space Telescope}进行了同期观测，用于设定扩展发射光通量的上限。
Spin and mass of the nearest supermassive black hole
围绕吸积黑洞的热等离子体斑点或团块的准周期振荡（QPO）包含了关于黑洞质量和自旋的信息。吸积流中亮点的纬向振荡频率和黑洞事件视界旋转的频率是测量黑洞质量和自旋的有希望的观测特征。这两个频率都与吸积模型无关，完全由黑洞引力场的性质定义。借助吸积等离子体热点的信号调制对已知的QPO数据进行解释，揭示了银河系中心超大质量黑洞的克尔度规旋转参数$a=0.65\pm0.05$和质量$M=(4.2\pm0.2)10^6M_\odot$。同时，将观测到的11.5 min QPO周期分别与黑洞事件视界旋转周期和吸积流热点纬向振荡周期相对应.所描述的方法是适用于黑洞的吸积率低，吸积等离子体是透明的事件视界区域。
Misalignment of the Lense-Thirring precession by an accretion torque
Indian Institute of Technology Indore（印度理工学院印多尔分校）；Northwestern University（西北大学）；Academy of Sciences（科学院）；Nicolaus Copernicus Astronomical Center（尼古拉·哥白尼天文中心）；College of Charleston（查尔斯顿学院）；Flatiron Institute（平研究所）
