Composite image of the giant barred spiral galaxy NGC 6872 combines visible light images from the European Southern Observatory's Very Large Telescope with far-ultraviolet data from NASA's Galaxy Evolution Explorer (GALEX) and infrared data acquired by NASA's Spitzer Space Telescope. NGC 6872 is 522,000 light-years across, making it more than five times the size of the Milky Way galaxy; in 2013, astronomers from the United States, Chile, and Brazil found it to be the largest-known spiral galaxy, based on archival data from GALEX.
When observed in the ultraviolet and mid-infrared, the central region and bar of NGC 6872 show old stars and low rates of star formation, with rates increasing along the spiral arms as distance from the core increases. The most active region of star formation, located in the northeast arm, shows a stellar flux around 1,000 times higher than in the central region, though this may be affected by the density of stellar dust in the core. The extended portions of both arms exhibit young star cluster formations with ages ranging from one to one hundred million years. Star formation rates in the northeast extended arm are twice that of the southwest extended arm, and five times the formation rate in the sections of the arms closer to the central region.
IC 4970 is a nearby lenticular galaxy, located only a few arcseconds away, and is known to be interacting with NGC 6872. Horrelou and Koribalski (2007), using a computer simulation to determine how the two galaxies were interacting, reported that IC 4970 approached NGC 6872 nearly along the plane of its spiral disk, making its closest approach approximately 130 million years ago and resulting in the latter's current highly elongated shape.
