Chandra Release - April 3, 2014

Visual Description: El Gordo

The image features a galaxy cluster known as El Gordo, which is one of the most massive galaxy clusters known in the universe.  The image of El Gordo is dominated by cloudy bright blue and magenta colors, creating contrast against the dark sky littered with tiny dots of light -  mostly distant galaxies and some foreground stars. This image is a composite image of X-rays from Chandra and optical data from Hubble of the galaxy cluster ACT-CL J0102-4915, located about 7 billion light years from Earth. This cluster has been nicknamed "El Gordo" (or, "the fat one" in Spanish) because of its gigantic mass. Data from Hubble suggests El Gordo weighs as much as 3 million billion times the mass of our Sun, and determined that most of the mass is hidden away as dark matter. The location of the dark matter is mapped out in this composite in blue. Because dark matter doesn't emit any radiation, astronomers instead precisely measure how its gravity warps the images of far background galaxies like a funhouse mirror. This allowed them to come up with a mass estimate for the cluster. Chandra's X-ray data are shown in magenta and these have been overlaid on optical data from Hubble that shows the individual galaxies in the cluster as well as stars in the field of view.  The X-ray image of El Gordo reveals a distinct cometary appearance, pointing to the left of the image and surrounded by blobs of blue. Along with the optical data, this shows that El Gordo is, in fact, the site of two galaxy clusters running into one another at several million miles per hour.