A recent image from the James Webb Space Telescope shows the most massive galaxy cluster we know of — one so large that it is nicknamed El Gordo, or the fat one. Thought to have a mass of over 2 quadrillion times the mass of the sun, the cluster is located 7 billion light-years away and hosts hundreds of galaxies that are gravitationally bound together.
The image was taken using Webb’s NIRCam instrument, which was able to capture the most detailed look yet at this enormous cluster and the many galaxies within it.
As the cluster has so much mass, images of it show a phenomenon called gravitational lensing, in which massive objects in the foreground bend space-time and magnify the light coming from distant background galaxies. That allows researchers to get a few of the extremely distant objects that would otherwise be too far away to see, like a galaxy called the Thin One (near the center of the image to the lower left) and the Fishhook (the red hook shape in the top right).
“Lensing by El Gordo boosts the brightness and magnifies the sizes of distant galaxies. This lensing effect provides a unique window into the distant universe,” explained Brenda Frye of the University of Arizona, a researcher who worked on analyzing these observations, in a statement.
Among the lensed objects in the data is a very young galaxy cluster in the first stages of forming, which is so far away it is seen as it was over 12 billion years ago. “While additional data are required to confirm that there are 17 members of this cluster, we may be witnessing a new galaxy cluster forming right before our eyes, just over a billion years after the big bang,” said Frye.
Researchers recorded this data as part of a project called PEARLS (Prime Extragalactic Areas for Reionization and Lensing Science) which uses Webb observations to look for these lensed objects. “Gravitational lensing was predicted by Albert Einstein more than 100 years ago. In the El Gordo cluster, we see the power of gravitational lensing in action,” said Rogier Windhorst of Arizona State University, principal investigator of the PEARLS program. “The PEARLS images of El Gordo are out-of-this-world beautiful. And, they have shown us how Webb can unlock Einstein’s treasure chest.”
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