Which massive galaxy cluster, nicknamed “El Gordo,” was imaged by JWST? The answer is El Gordo. Its formal designation is ACT-CL J0102-4915, also catalogued as SPT-CL J0102-4915.
El Gordo means “the Fat One” in Spanish, a nickname inspired by the cluster’s extraordinary mass. It lies in the constellation Phoenix, more than 7 billion light-years from Earth, and is made of two enormous galaxy subclusters colliding at several million kilometres per hour.
JWST observed El Gordo in July 2022 using its Near Infrared Camera, or NIRCam. The cluster’s immense gravity acts as a gravitational lens, bending and magnifying light from much more distant galaxies behind it. This produced striking distorted arcs and helped astronomers study faint objects in the early universe.
El Gordo is sometimes confused with the Bullet Cluster, another famous merging galaxy cluster. The two systems have similar collision-driven structures, but they are separate objects. El Gordo was first identified through observations involving the Atacama Cosmology Telescope, NASA’s Chandra X-ray Observatory, and the Very Large Telescope before JWST added its detailed infrared view.