Here is the official definition from wikipedia of this term:

A gravitational lens refers to a distribution of matter (such as a cluster of galaxies) between a distant source and an observer, that is capable of bending the light from the source, as it travels towards the observer. This effect is known as gravitational lensing and the amount of bending is one of the predictions of Albert Einstein‘s general theory of relativity.^[1][2] (Classical physics also predicts bending of light, but only half that of general relativity’s.^[3])

Although either Orest Khvolson (1924) or Frantisek Link (1936) is sometimes credited as being the first one to discuss the effect in print, the effect is more commonly associated with Einstein, who published a more famous article on the subject in 1936.

Fritz Zwicky posited in 1937 that the effect could allow galaxy clusters to act as gravitational lenses. It was not until 1979 that this effect was confirmed by observation of the so-called “Twin QSO” SBS 0957+561.

This technique gives many astronomers a perspective previously impossible with typical methods.  And they are just starting to find out more about black holes.

We hope you enjoy the video and this year may have some incredible new pics using this method!