Well positioned in the evening sky for viewers in the northern hemisphere, Messier 2, also known as NGC 7089, is one of the largest globular clusters known, with about 150,000 stars stretching across 175 light years. Thought to be about 13 billion years old, the cluster’s eccentric orbit carries it as far as 171,000 light years from the center of the Milky Way and up to 165,000 light years above and below the galactic plane. Currently about 55,000 light years from Earth in the constellation Aquarius, M2 was discovered by the French astronomer Jean-Dominique Maraldi in 1746 and added to Charles Messier’s famous list in 1760. It is visible to the unaided eye on extraordinarily clear nights and easily resolved into a spectacular star swarm in moderate-size telescopes. As viewed by the Hubble Space Telescope, as seen here, M2 is nothing short of jaw dropping, with a dense core of close-packed stars.
It is known today that merging galaxies play a large role in their evolution, and the formation of elliptical galaxies in particular. However, there are only a few merging systems close enough to be observed in depth. The pair of interacting galaxies seen here — known as NGC 3921 — is one of these systems. But ‘close’ is a relative term: NGC 3921 lies 270 million light-years away.