Astronomers discovered these two distant galaxies in the same small part of the sky. They estimate that the one on the right is from 300 million years after the Big Bang. Credit: JWST GLASS Survey NASA/CSA/ESA/STScI; Pascal Oesch/University of Geneva
NASA built its state-of-the-art James Webb Space Telescope to peer into the distant universe and back to the dawn of time — and it’s already doing it impressively. In the two weeks since Webb’s first science images and data became available to astronomers, they have reported a flurry of preliminary discoveries, including multiple contenders for what could be the most distant galaxy ever seen.
Webb’s images reveal a wealth of galaxies glimmering in distant space, appearing as they did just a few hundred million years after the Big Bang 13.8 billion years ago. The telescope’s amazingly clear pictures shattered astronomers’ preconceptions about the early universe.
“We meant an idea of what galaxies are here [distances] it would seem and how much detail we could see, but I think the reality just amazes us,” says Ceyhan Kartaltepe, an astronomer at the Rochester Institute of Technology in New York.
Here are some things astronomers are learning from Webb’s first observations.
There are an awful lot of galaxies out there.
Because Webb detects infrared light, and because the expansion of space stretches light to redder wavelengths, the telescope is well-suited for spotting galaxies that formed early in the universe’s history. In its first observing programs, which began in June, Webb discovered many distant galaxies that lie beyond the reach of other observatories, such as the Hubble Space Telescope.
“This suggests that many of us are arguing that there are galaxies beyond what we saw with Hubble,” said Richard Ellis, an astronomer at University College London.
The era of early galaxies begins at the “cosmic dawn,” beginning perhaps about 250 million years after the Big Bang, when the first stars formed and lit up the universe. Later generations of stars accumulate into galaxies, which are faint red blobs that Webb is beginning to detect.
Many of Webb’s images are dotted with never-before-seen galaxies in the distant universe. “There’s hardly an empty space that doesn’t have something in it,” says Kartaltepe.
One study analyzed data from many of the distant galactic fields Webb has observed so far to analyze the rate at which stars formed in the early universe. It discovered 44 previously unknown galaxies stretching within 300 million years of the Big Bang. Combined with 11 previously known galaxies, the findings show that there was a significant population of star-forming galaxies in the early Universe1. The results “reaffirm the enormous potential of upcoming larger [Webb] programs to transform our understanding of the young universe,” the team led by Calum Donnan of the University of Edinburgh, UK, wrote in a paper on the arXiv preprint server.
Many galaxies compete for the title of “most distant”.
Perhaps the most famous rush is the flight of research teams competing to identify the most distant galaxy in the Webb data. A number of candidates have been spotted, which will need to be confirmed by further studies, but all of them would break Hubble’s record for the most distant galaxy, which dates back to about 400 million years after the Big Bang2,3.
Maisie’s Galaxy: Astronomer Steven Finkelstein named this distant galaxy after his daughter. He estimates that it is from 280 million years after the Big Bang. Credit: Steven Finkelstein (UT Austin), Michaela Bagley (UT Austin), Casey Papovich (Texas A&M) and the CEERS team
One contender emerged in a Webb survey called GLASS, which includes another, slightly less distant galaxy in the same image4. “The fact that we found these two bright galaxies was really a surprise,” says Marco Castellano, an astronomer at the National Institute of Astrophysics in Rome. He and his colleagues did not expect to find such distant galaxies in this small part of the sky. A second team also independently spotted the two galaxies5.
Astronomers characterize the distance of galaxies with a measure known as redshift, which quantifies how much a galaxy’s light is shifted toward redder wavelengths; the higher the redshift, the more distant the galaxy. The GLASS candidate has a redshift of about 13. But on July 25 and 26, days after astronomers reported the GLASS galaxies, papers claiming even higher redshifts flooded the arXiv preprint server. “This is just the beginning of the beginning,” said Rohan Naidu, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
One candidate, at redshift 14, appeared in a survey called CEERS, one of Webb’s highest-profile early projects. CEERS principal investigator Steven Finkelstein of the University of Texas at Austin named the object the Maisie Galaxy after his daughter6. Another study looked at the first Webb deep-field image, released by US President Joe Biden on July 11, and found two potential galaxies at a redshift of 16, placing them just 250 million years after the Big Bang7. And other arXiv papers speculate other candidates, even up to redshifts of 208.
Some early galaxies are surprisingly complex.
Webb’s distant galaxies also turn out to have more structure than astronomers expected.
A study of the first deep-field Webb image found a surprisingly large number of distant galaxies that have the shape of discs9. Using Hubble, astronomers concluded that distant galaxies are more irregular in shape than nearby ones, which, like the Milky Way, often exhibit regular disk-like shapes. The theory was that early galaxies were more often distorted by interactions with neighboring galaxies. But Webb’s observations suggest there are up to 10 times more distant disc-shaped galaxies than previously thought.
US President Joe Biden released this deep-field image on July 11 — the first scientific view from the Webb to be released publicly. Credit: NASA, ESA, CSA and STScI
“With James Webb’s resolution, we can see that galaxies have disks much earlier than we thought they did,” said Alison Kirkpatrick, an astronomer at the University of Kansas in Lawrence. This is a problem, she says, because it contradicts earlier theories of galaxy evolution. “We’ll have to figure that out.”
Another preprint manuscript suggests that massive galaxies formed earlier in the universe than previously known. A team led by Ivo Labbe of Swinburne University of Technology in Melbourne, Australia, reports finding seven massive galaxies in the CEERS field, with redshifts between 7 and 1010. “We infer that the central regions of at least some massive galaxies were already largely in place 500 million years after the Big Bang, and this massive galaxy formation began extremely early in the history of the universe,” the scientists wrote.
Studies of galactic chemistry also show a rich and complex picture emerging from the Webb data. One analysis of the first deep-field image examines the light emitted by galaxies at redshift 5 or greater. (Spectral lines that appear at different wavelengths of light correlate with the chemical elements that make up galaxies.) He found a surprising wealth of elements such as oxygen11. Astronomers thought the process of chemical enrichment – where stars fuse hydrogen and helium to form heavier elements – took some time, but the finding that it is underway in early galaxies “will make us rethink the rate at which star formation happens,” Kirkpatrick says.
Closer galaxies are smaller than expected.
Webb’s surprises continue a little later in the evolution of the universe. One study looked at Webb’s observations of the “cosmic noon,” the period roughly 3 billion years after the Big Bang. This is when star formation peaked in the universe and the most light was created.
Ren Suess, an astronomer at the University of California, Santa Cruz, compared Hubble’s images of galaxies at cosmic noon with Webb’s images of the same galaxies. At the infrared wavelengths detected by Webb, most of the massive galaxies appeared much smaller than in the Hubble images12. “This potentially changes our whole view of how galaxy sizes evolve over time,” Suess says. Hubble’s studies suggested that galaxies were initially small and grew over time, but Webb’s findings suggest that Hubble did not have the whole picture, and therefore the evolution of galaxies may be more complex than scientists expected.
As Webb is at the beginning of what is planned to be more than 20 years of work, astronomers know that many changes are ahead. “Right now I find myself lying awake at three in the morning,” says Kirkpatrick, “and wondering if everything I’ve done is wrong.”
Add Comment