satellite galaxies. Slightly fainter is NGC 5921, a barred spiral galaxy with a LINER-type active galactic nucleus situated somewhat closer at a distance of 21 megaparsecs. A type II supernova was observed in this galaxy in 2001 and was designated SN 2001X. Fainter still are the spirals NGC 5964 and NGC 6118, with the latter being host to the supernova SN 2004dk. Hoag's Object, located 600 million light-years from Earth, is a member of the very rare class of galaxies known as ring galaxies. The outer ring is largely composed of young blue stars while the core is made up of older yellow stars. The predominant theory regarding its formation is that the progenitor galaxy was a barred spiral galaxy whose arms had velocities too great to keep the galaxy's coherence and therefore detached. Arp 220 is another unusual galaxy in Serpens. The prototypical ultraluminous infrared galaxy, Arp 220 is somewhat closer than Hoag's Object at 250 million light-years from Earth. It consists of two large spiral galaxies in the process of colliding with their nuclei orbiting at a distance of 1,200 light-years, causing extensive star formation throughout both components. It possesses a large cluster of more than a billion stars, partially covered by thick dust clouds near one of the galaxies' core. Another interacting galaxy pair, albeit in an earlier stage, consists of the galaxies NGC 5953 and NGC 5954. In this case, both are active galaxies, with the former a Seyfert 2 galaxy and the latter a LINER-type galaxy. Both are undergoing a burst of star formation triggered by the interaction. Seyfert's Sextet is a group of six galaxies, four of which are interacting gravitationally and two of which simply appear to be a part of the group despite their greater distance. The gravitationally bound cluster lies at a distance of 190 million light-years from Earth and is approximately 100,000 light-years across, making Seyfert's Sextet one of the densest galaxy group known. Astronomers predict that the four interacting galaxies will eventually merge to form a large elliptical galaxy. The radio source 3C 326 was originally though to emanate from a giant elliptical galaxy. However, in 1990, it was shown that the source is instead a brighter, smaller galaxy a few arcseconds north. This object, designated 3C 326 N, has enough gas for star formation, but is being inhibited due to the energy from the radio galaxy nucleus. A