The Einstein Cross Gravitational Lens . ... WIYN , AURA , NOAO , NSF Explanation: Most galaxies have a single nucleus -- does this galaxy have four? ... The general effect is known as gravitational lensing , and this specific case is known as the Einstein Cross . Stranger still, the images of the Einstein Cross vary in relative brightness, enhanced occasionally by the additional gravitational microlensing effect of specific stars in the foreground galaxy. ... NASA Official: Jay Norris. ...