Gravitational Lensing (Gravitational Mirage) - Because light can be bent by the gravity of massive objects: 1. Objects viewed passing in front of other objects creates a visible distortion of the fabric space-time by the gravitation of the object (such as a galaxy) behind it. 2. Light from objects which are behind other objects is bent around the foreground object, displacing and making visible the background object, creating a lens-shaped ring of light, or even appearing multiple times around the foreground object.
This image is a simulation of a black hole passing in front of a background galaxy.