‘The Fat One’: Largest, Hottest And Brightest X-ray Galaxy Cluster Ever Found In Distant Universe

A few years ago, astronomers have focused their attention on an extremely hot, massive young galaxy cluster, officially known as ACT-CLJ0102-4915.

This gigantic galaxy cluster has been nicknamed ‘El Gordo’ (‘the Fat One’ in Spanish) because it is the largest, hottest, and X-ray brightest galaxy cluster ever seen in the distant Universe!

This picture of the galaxy cluster ACT-CL J0102−4915 combines images taken with ESO’s Very Large Telescope with images from the SOAR Telescope and X-ray observations from NASA’s Chandra X-ray Observatory. The X-ray image shows the hot gas in the cluster and is shown in blue. This newly discovered galaxy cluster has been nicknamed El Gordo — the “big” or “fat one” in Spanish. It consists of two separate galaxy subclusters colliding at several million kilometres per hour, and is so far away that its light has travelled for seven billion years to reach the Earth. Credit: ESO/SOAR/NASA

‘The Fat One’ contains the mass of a staggering three million billion Suns and it has been studied with the help of ESO’s Very Large Telescope (VLT) in the Atacama Desert in Chile along with NASA’s Chandra X-ray Observatory and the Atacama Cosmology Telescope.

It was also determined that ‘the Fat One’, is actually composed of two galaxy clusters colliding at millions of kilometers per hour.

Galaxy clusters are the largest objects in the Universe that are bound together by gravity. They form over billions of years as smaller groups of galaxies slowly come together. Their formation depends heavily on dark matter and dark energy. El Gordo’s “normal” matter — largely composed of hot gas that is bright in the X-ray wavelength domain — is being torn from the dark matter in the collision. The hot gas is slowing down, while the dark matter is not.

El Gordo is so far away from Earth that its light has travelled for seven billion years to reach us.

“This cluster is the most massive, the hottest, and gives off the most X-rays of any cluster found so far at this distance or beyond,” said Felipe Menanteau of Rutgers University, who led the study.

“We devoted a lot of our observing time to El Gordo, and I’m glad our bet paid off and we found an amazing cluster collision.”

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