NASA’s Hubble Space Telescope has weighed the largest known galaxy cluster in the distant universe, catalogued as ACT-CL J0102-4915, and found it definitely lives up to its nickname — El Gordo (Spanish for “the fat one”).
By measuring how much the cluster’s gravity warps images of galaxies in the distant background, a team of astronomers has calculated the cluster’s mass to be as much as 3 million billion times the mass of our sun. Hubble data show the galaxy cluster, which is 9.7 billion light-years away from Earth, is roughly 43 percent more massive than earlier estimates.
The team used Hubble to measure how strongly the mass of the cluster warped space. Hubble’s high resolution allowed measurements of so-called “weak lensing,” where the cluster’s immense gravity subtly distorts space like a funhouse mirror and warps images of background galaxies. The greater the warping, the more mass is locked up in the cluster.
Seven billion light-years from Earth, two galaxy subclusters are colliding at a speed of several million kilometers per hour. While it is officially known as ACT-CL J0102-4915, the results of this collision are nicknamed ‘El Gordo,’ which is Spanish for “The fat one” or “The big one.”
El Gordo has earned its moniker. At 2 quadrillion times the mass of our Sun, the cluster is the largest known in the Universe. El Gordo was discovered by scientists at the Chandra X-Ray Observatory, and is a place of many extremes. According to researchers, this cluster is also the hottest and gives off the most X-rays of all the known clusters in the distant Universe.
Stars make up only about 1% of the cluster’s mass, with the rest composed of hot gas that can reach searing temperatures of 200 million degrees Celsius. The galaxy at its center emits extremely bright bluish light and is believed to be the aftermath of a galactic merger.
Researchers hope that studying El Gordo will unravel some mysteries about dark matter and energy. As El Gordo’s subclusters merge, the force of the collision slows down the gas but not the dark matter, wrenching them apart. This, as well as several other characteristics, leads researchers to believe that El Gordo formed in a manner similar to the Bullet Cluster (click here for info on the Bullet cluster).
Despite its extreme characteristics, El Gordo fits within current models of the Big Bang, though it is at the upper limit of what our cosmology can explain.
Image: X-ray: NASA/CXC/Rutgers/J.Hughes et al, Optical: ESO/VLT/Pontificia Universidad. Catolica de Chile/L.Infante & SOAR (MSU/NOAO/UNC/CNPq-Brazil)/Rutgers/F.Menanteau, IR: NASA/JPL/Rutgers/F.Menanteau