Webb telescope draws back the curtain on universe’s early galaxies

Initial findings from JWST Early Release Science programs include the discovery of two exceptionally bright galaxies in the early universe

images of early galaxies
Two of the farthest galaxies seen to date are captured in these James Webb Space Telescope pictures. The galaxy labeled (1) existed only 450 million years after the big bang. The galaxy labeled (2) existed 350 million years after the big bang. Both are seen very close in time to the big bang, which occurred 13.8 billion years ago. These galaxies are tiny compared to our Milky Way, being just a few percent of its size, even the unexpectedly elongated galaxy labeled (1). [Science Credits: NASA, ESA, CSA, Tommaso Treu (UCLA); Image Processing: Zolt G. Levay (STScI)]
images of galaxy cluster showing distant galaxy beyond it
The distant galaxies were found in these JWST images (above and below) of the outer regions of the giant galaxy cluster Abell 2744. The galaxies are not inside the cluster, but many billions of light-years farther behind it. [Science Credits: NASA, ESA, CSA, Tommaso Treu (UCLA); Image Processing: Zolt G. Levay (STScI)]
images of galaxy cluster showing distant galaxy beyond it

NASA’s James Webb Space Telescope (JWST) has found an unexpectedly rich realm of early galaxies that has been largely hidden until now, beyond the reach of other telescopes.

Researchers have found two exceptionally bright galaxies that existed approximately 350 and 450 million years after the big bang. These and other observations are nudging astronomers toward a consensus that an unusual number of galaxies in the early universe were much brighter than expected.

“We’ve nailed something that is incredibly fascinating. These galaxies would have 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 Garth Illingworth, professor emeritus of astronomy and astrophysics at UC Santa Cruz. “The primal universe would have been just one hundredth its current age. It’s a sliver of time in the 13.8-billion-year-old evolving cosmos.”

Two research papers, led by Marco Castellano of the National Institute for Astrophysics in Rome, Italy, and Rohan Naidu of the Harvard-Smithsonian Center for Astrophysics and the Massachusetts Institute of Technology in Cambridge, Massachusetts, have been published in Astrophysical Journal Letters. Illingworth is a coauthor of the Naidu et al. paper.

These initial findings are from a broader JWST research initiative involving two Early Release Science (ERS) programs: the Grism Lens-Amplified Survey from Space (GLASS), and the Cosmic Evolution Early Release Science Survey (CEERS).

“Everything we see is new. Webb is showing us that there's a very rich universe beyond what we imagined,” said Tommaso Treu at UCLA, a principal investigator on one of the Webb programs. “Once again, the universe has surprised us. These early galaxies are very unusual in many ways.”

With just four days of analysis, researchers found the two exceptionally bright galaxies in the GLASS-JWST images. These galaxies existed approximately 450 and 350 million years after the big bang (with a redshift of approximately 10.5 and 12.5, respectively). Future spectroscopic measurements with JWST are needed to confirm their distances.

“While the distances of these early sources still need to be confirmed with spectroscopy, their extreme brightnesses are a real puzzle, challenging our understanding of galaxy formation,” noted Pascal Oesch at the University of Geneva in Switzerlandd, second author of the Naidu et al. paper.

“With Webb, we were amazed to find the most distant starlight that anyone had ever seen, just days after Webb released its first data," said Naidu of the more distant GLASS galaxy, referred to as GLASS-z12, which is believed to date back to 350 million years after big bang. The previous record holder is galaxy GN-z11, which existed 400 million years after the big bang (redshift 11.1) and was identified in 2016 by Hubble and Keck Observatory in deep-sky programs.

“Based on all the predictions, we thought we had to search a much bigger volume of space to find such galaxies,” said Castellano.

Another surprise was the discovery of galaxies with compact disks at such early times, which was only possible because of JWST’s much sharper images, in infrared light, compared to Hubble.

"Our team was struck by being able to measure the shapes of these first galaxies; their calm, orderly disks question our understanding of how the first galaxies formed in the crowded, chaotic early universe," said team member Erica Nelson of the University of Colorado.

Illingworth emphasized the two bright galaxies found by these teams have a lot of light. He said one option is that they could have been very massive, with lots of low-mass stars, like later galaxies. Alternatively, they could be much less massive, consisting of far fewer extraordinarily bright stars, known as Population III stars. Long theorized, they would be the first stars ever born, blazing at blistering temperatures and made up only of primordial hydrogen and helium—before stars could later cook up heavier elements in their nuclear fusion furnaces. No such extremely hot, primordial stars are seen in the local universe.

“Indeed, the farthest source is very compact, and its colors seem to indicate that its stellar population is particularly devoid of heavy elements and could even contain some Population III stars. Only Webb spectra will tell,” said Adriano Fontana, second author of the Castellano et al. paper and a member of the GLASS-JWST team.

Present Webb distance estimates to these two galaxies are based on measuring their infrared colors. Eventually, follow-up spectroscopy measurements showing how light has been stretched in the expanding universe will provide independent verification of these cosmic yardstick measurements.

“The secrets of the earliest galaxies are only now starting to be revealed by Webb—the real discoveries lie ahead,” Illingworth said.

The James Webb Space Telescope is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).