Image Credit & Copyright: J. Rhoads (Arizona State U.) et al., WIYN, AURA, NOAO, NSFExplanation: Most galaxies have a single nucleus — does this galaxy have four? The strange answer leads
astronomers to conclude that the nucleus of the surrounding galaxy is not even visible in
this image. The central
cloverleaf is rather light emitted from a background
quasar. The
gravitational field of the visible foreground galaxy
breaks light from this distant
quasar into four distinct images. The
quasar must be properly aligned behind the center of a massive galaxy for a
mirage like this to be evident. 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.