Relativistic Effects on the Appearance of a Clothed Black Hole
  For an accretion disk around a black hole, the strong relativistic effects affect every aspect of the radiation from the disk, including its spectrum, light-curve, and image. This work investigates in detail how the images of a thin disk around a black hole will be distorted, and what the observer will see from different viewing angles and in different energy bands. 
Xiaoling Zhang, S.Nan Zhang, Yuxin Feng, Yangsen Yao