Gallery | Pics from AAS 219 in Jan 2012 | El Gordo, a cluster halfway across the Universe
A combination of observations using the orbiting Chandra X-Ray Observatory and the ground-based Very Large Telescope and Atacama Cosmology Telescope has found the largest galaxy cluster ever seen in the distant Universe. They've nicknamed it El Gordo, meaning the fat man in Spanish.
It's actually the result of two clusters colliding. The image is dominated by X-rays (colored blue in the picture) being emitted by gas heated to millions of degrees by the collision. The cluster was found in a survey of how matter distorts the light from the far more distant background glow of the sky emitted by the Big Bang itself. They knew the cluster was big, and when they pointed Chandra at it they knew it was terribly hot from the collision as well. The most amazing thing is its distance: seven billion light years! Knowing how clusters behave at such huge distances helps astronomers understand how the Universe has changed over time, and how the largest structures in the cosmos came to be.