Gravitational lensing: The Einstein Cross

Graphic - gravlens

Since a gravitational force deflects light, matter can act as a lens.

In the above picture the image at the centre is that of a galaxy; surrounding it there are four other images. But all four are actually images of the same object (a quasar lying beyond the galaxy). This ‘optical illusion’ is created by the way the galaxy bends the light from the quasar. The image is called an ‘Einstein Cross’