Radiating like a luminous lighthouse amid a cosmos filled with galaxies, Arp 220 brightens the celestial panorama as seen by NASA’s James Webb Space Telescope. Arp 220, in fact, is not a single entity but a pair of intertwined spiral galaxies on their path towards a full-fledged merger. This celestial marvel is most radiant in the infrared spectrum, marking it as a perfect observational candidate for the Webb telescope. Classified as an ultra-luminous infrared galaxy (ULIRG), its luminosity surpasses a trillion suns, dwarfing our home galaxy, the Milky Way, which has a modest luminosity of about ten billion suns.
Situated 250 million light-years distant in the Serpens constellation, or the Serpent, Arp 220 is the 220th entry in Halton Arp’s Atlas of Peculiar Galaxies. It holds the distinction of being the nearest ULIRG and the most luminous among the three closest galactic mergers to Earth.
The ongoing cosmic collision between the two spiral galaxies started approximately 700 million years ago, igniting a significant surge in star formation. About 200 enormous star clusters are confined in a compact, dust-filled region spanning roughly 5,000 light-years, or about 5 percent of the Milky Way's diameter. The amount of gas present in this relatively minuscule area matches the entire gas content of the Milky Way.
Prior observations using radio telescopes disclosed around 100 supernova remnants within a region spanning less than 500 light-years. NASA’s Hubble Space Telescope managed to unmask the nuclei of the original galaxies, separated by 1,200 light-years. Each of these cores houses a rotating ring of star-forming regions, responsible for the intense infrared luminosity so evident in the image captured by the Webb telescope. This intense radiance forms diffraction spikes, creating the starburst feature that takes center stage in this image.
On the fringes of this cosmic collision, the Webb telescope has captured faint tidal tails, showcased in blue—gravitational signs of the ongoing intergalactic ballet. Traces of organic material, depicted in shades of reddish-orange, streak across Arp 220 in streams and filaments.
The portrait of Arp 220 was captured by Webb's Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI).