El Gordo Is The Biggest Galaxy Cluster Ever Seen In The Early Universe

Brilliance | Dec. 16, 2017

The El Gordo galaxy cluster is big. How big is it? It's so big that it would take 3,000 Milky Way galaxies to equal its mass. It's so big that it weighs as much as 3 quadrillion suns. It's so big that a 2012 estimate said it was massive, and then a 2014 estimate said no, it's nearly twice that massive.

El Gordo sits in an area of space more than 7 billion light years from Earth. That means we're seeing it as it was 7 billion years ago—when the universe was half as old as it is today. That's what makes it so interesting to researchers. There are larger galaxy clusters out there, but this is the most massive one we've seen so early in the universe.

In January 2012, an international team used NASA's Chandra X-ray Observatory and the European Southern Observatory's Very Large Telescope Array to calculate El Gordo's mass. By examining the temperatures of gases, movement of galaxies, and the distortion of background radiation, the team put the cluster's mass at approximately 2 quadrillion suns (that's a 2 with 15 zeroes). This measurement came with plenty of uncertainty, mostly because El Gordo may not be one cluster, but a combination of two. In 2014, the Hubble Space Telescope took a second look, this time measuring how much the cluster's gravity warps the light coming from galaxies behind it. This more precise measure came up with a number 43 percent bigger than the one in 2012, putting El Gordo at approximately the mass of 3 quadrillion suns. A number that big is far too much for the human mind to comprehend, but the videos below might help.

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