This image from the NASA/ESA Hubble Space Telescope features Arp 72, a very selective galaxy group that only includes two galaxies interacting due to gravity: NGC 5996 (the large spiral galaxy) and NGC 5994 (its smaller companion, in the lower left of the image).

"Photographing Andromeda was a herculean task because the galaxy is a much bigger target on the sky than the galaxies Hubble routinely observes, which are often billions of light-

Messier 31 is located 2.5 million light-years away from Earth and was a much bigger target in the sky than the galaxies Hubble routinely observes.