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James Webb spots two of the earliest galaxies ever seen

The James Webb Space Telescope has discovered two of the earliest galaxies ever seen in the universe, and they are much brighter than expected, meaning astronomers are rethinking their beliefs about how the earliest stars formed.

“These observations just make your head explode,” said Paola Santini, one of the researchers, in a statement. “This is a whole new chapter in astronomy. It’s like an archaeological dig, when suddenly you find a lost city or something you didn’t know about. It’s just staggering.”

Two of the most distant galaxies seen to date are captured in these Webb pictures of the outer regions of the giant galaxy cluster Abell 2744. The galaxies are not inside the cluster, but many billions of light-years behind it. 
Two of the most distant galaxies seen to date are captured in these Webb pictures of the outer regions of the giant galaxy cluster Abell 2744. The galaxies are not inside the cluster, but many billions of light-years behind it. NASA, ESA, CSA, T. Treu (UCLA)

The two galaxies are thought to be billions of years old, from just 100 million years after the Big Bang. Webb is able to look back at some of the earliest galaxies, because it operates in the infrared range, meaning it can see galaxies that are redshifted.

Redshift happens when light from a distant galaxy is shifted to the red end of the spectrum because of the expansion of the universe. The stronger the shift, the more distant the galaxy. The light from some galaxies is shifted so far that it moves out of the visible light spectrum and into the infrared, where Webb can see it. Previous research had estimated that some galaxies Webb detected could have a redshift as high as 14, but the recent results are more accurate thanks to better calibration of the instruments and suggest a redshift for the two galaxies of 10.5 and 12.5, respectively.

Webb also takes advantage of a phenomenon called gravitational lensing, in which a massive object like a galaxy or galaxy cluster has so much mass that it warps space and acts like a magnifying glass, allowing researchers to see even more distant galaxies behind it.

The big surprise is that both of the galaxies observed are much brighter than researchers had thought they would be. They were also spotted very quickly, in the first few days of Webb observations, suggesting that early galaxies could be more numerous than previously thought.

“We’ve nailed something that is incredibly fascinating. These galaxies would have had to have started coming together maybe just 100 million years after the Big Bang. Nobody expected that the dark ages would have ended so early,” said another of the researchers, Garth Illingworth. “The primal Universe would have been just one hundredth of its current age. It’s a sliver of time in the 13.8-billion-year-old evolving cosmos.”

The researchers suggest that either the early galaxies could be much more massive than thought, with many more stars than expected, or that they could be less massive but with stars that shined very brightly and are quite different from the stars we see today. To learn more and to confirm the age of these universes, the researchers plan to perform more observations with Webb’s spectroscopy instruments.

“Everything we see is new. Webb is showing us that there’s a very rich universe beyond what we imagined,” said researcher Tommaso Treu. “Once again the universe has surprised us. These early galaxies are very unusual in many ways.”

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