When astronomers disco

When astronomers discovered the galaxy cluster ACT-CL J0102-4915 in 2012 with NASA’s Chandra X-ray Observatory and ground-based optical telescopes, they nicknamed it “El Gordo” (Spanish for the “Fat One”) because of its gigantic mass.

Scientists estimate that El Gordo contains as much as 3 million billion (3,000,000,000,000,000) times the mass of the Sun. Thanks to its heft, El Gordo acts as a natural lens, distorting the light from more distant objects behind it through a process known as gravitational lensing.

A new composite image of El Gordo shows the diffuse, superheated gas in the cluster observed in X-rays from Chandra (blue) that have been combined with a new infrared image from NASA’s James Webb Space Telescope (red, green, and blue). Webb’s image shows galaxies in El Gordo plus background galaxies located further away from Earth. El Gordo is located about 7.3 billion light-years from Earth and the background galaxies are at a range of different distances including several that are 12.3 billion light-years from Earth. The appearance of some of the background galaxies has been distorted into a variety of unusual and highly elongated shapes because of gravitational lensing by the cluster.

The X-ray image of El Gordo reveals a distinct cometary appearance. Along with optical data, astronomers reported in 2012 that this shape implies El Gordo is, in fact, the site of two galaxy clusters that ran into one another at several million miles per hour. The same study also used Chandra and other observatories to show that El Gordo is the most massive, and produces the most X-rays, of any known galaxy cluster at its distance or beyond.

Image credit: X-ray: NASA/CXC/Rutgers/J. Hughes et al.; Infrared: NASA/ESA/CSA, J.M. Diego (IFCA), B.Frye (Univ. of Arizona), P.Kamieneski, T.Carleton & R.Windhorst (ASU); Image processing: X-ray: L. Frattare; J. Major, K.Arcand (SAO). Infrared: A.Pagan (STScI), J.Summers (ASU), J.C.J.D’Silva (UWA), A.M.Koekemoer (STScI), A.Robotham (UWA), R.Windhorst (ASU) Larger image