Super-Sized "El Gordo" Galaxy Cluster is Oldest, Most Massive Known

A distant galaxy cluster known as "El Gordo" lives up to its massive reputation; astronomers have calculated the cluster's mass to be 3 million times the mass of our Sun.

El Gordo - Spanish for "the fat one" - is the largest known galaxy cluster in the distant universe, about 9.7 billion light years away from Earth. The new calculations of El Gordo reveal it to be 43 percent more massive than earlier estimates, NASA reported.

The Hubble Space Telescope was used to measure the mass of El Gordo, which is technically classified as ACT-CL J0102-4915. The Hubble was able to measure what's known as "weak lensing," a phenomenon where gravity slightly distorts space to appear like a funhouse mirror, warping the images of background galaxies. The greater the distortion, the more massive the cluster.

James Jee, of the University of California at Davis, was the principle investigator of the El Gordo study.

"What I did is basically look at the shapes of the background galaxies that are farther away than the cluster itself," Jee said in a statement. "It's given us an even stronger probability that this is really an amazing system very early in the universe."

The mass of El Gordo is locked up several hundred galaxies and the hot gases that fill out the clusters, but the bulk of it is accounted for as dark matter.

The El Gordo cluster is a cosmological rarity. While similarly massive clusters have been found closer to Earth, El Gordo is the most massive galaxy cluster found so far back in time.

The galaxy cluster is so massive that Hubble cannot fit it into its field of vision. Instead, the cluster has to be imaged in sections and then viewed as a whole as a mosaic. Viewing it this way, the researchers said, is like viewing a giant from its side.

"We can tell it's a pretty big El Gordo, but we don't know what kind of legs he has, so we need to have a larger field of view to get the complete picture of the giant," said Felipe Menanteau of the University of Illinois at Urbana-Champaign.