Astronomers found these two distant galaxies in the same small part of the sky. They estimate that the one on the right is 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 toward the dawn of time, and it’s already doing so spectacularly. In the two weeks since Webb’s first images and science data became available for astronomers to work with, they’ve reported a slew of preliminary discoveries, including multiple contenders for what could be the most distant galaxy ever seen.
Webb’s images reveal a wealth of glowing galaxies in the distant cosmos, appearing as they did a few hundred million years after the Big Bang 13.8 billion years ago. The telescope’s astonishingly sharp images have shattered astronomers’ preconceptions about the early Universe.
“We had an idea in mind of which galaxies in these [distances] it would seem, and how much detail we could see, but I think the reality just blows our minds,” says Jeyhan Kartaltepe, an astronomer at the Rochester Institute of Technology in New York.
Here are some things astronomers are learning from Webb’s early observations.
There are a lot of galaxies out there.
Because Webb detects infrared light, and because the expansion of the cosmos stretches the light to redder wavelengths, the telescope is well-suited to detect galaxies that formed early in the Universe’s history. In its first observing programs, which began in June, Webb discovered many distant galaxies that are beyond the reach of other observatories, such as the Hubble Space Telescope.
“It suggests what many of us have been discussing, that there are galaxies beyond what we saw with Hubble,” says Richard Ellis, an astronomer at University College London.
The era of the first galaxies began at the “cosmic dawn,” beginning perhaps 250 million years after the Big Bang, when the first stars formed and lit up the Universe. Subsequent generations of stars clustered into galaxies, which are the faint red spots that Webb is beginning to discover.
Many of Webb’s images are full of never-before-seen galaxies in the distant Universe. “There is practically no empty space that has nothing,” says Kartaltepe.
A study analyzed data from many of the distant galaxy fields Webb has observed so far, to analyze the rate at which stars formed in the early Universe. It found 44 previously unknown galaxies dating back 300 million years after 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 to scale up [Webb] programs to transform our understanding of the young Universe,” the team, led by Callum Donnan of the University of Edinburgh, UK, wrote in a paper on the arXiv preprint server.
Many galaxies compete for the “farthest” title.
Perhaps the most notable rush is the stampede of research teams scrambling to identify the most distant galaxy in Webb’s data. A number of candidates have been detected that will need to be confirmed by further studies, but all 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. Estimate that it is 280 million years after the Big Bang. Credits: Steven Finkelstein (UT Austin), Micaela Bagley (UT Austin), Casey Papovich (Texas A&M) and the CEERS team
A contender appeared in a Webb survey called GLASS that included another slightly less distant galaxy in the same image4. “Finding 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 any such distant galaxies in this small part of the sky. A second team also independently detected the two galaxies5.
Astronomers characterize the distance of galaxies with a measure known as redshift, which quantifies how much a galaxy’s light has shifted to 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,” says Rohan Naidu, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
One candidate, at a redshift of 14, emerged in a survey called CEERS, one of Webb’s first high-profile projects. CEERS principal investigator Steven Finkelstein of the University of Texas at Austin named the object the Maisie Galaxy, after his daughter6. Another study analyzed Webb’s first deep-field image, released by US President Joe Biden on July 11, and found two potential galaxies at a redshift of 16, which would place them just 250 million d ‘years after the Big Bang7. And other arXiv papers speculate on other candidates, even redshifts of 208.
Some early galaxies are surprisingly complex.
Webb’s distant galaxies are also turning out to have more structure than astronomers expected.
A study of the first Webb deep-field image found a surprisingly large number of distant galaxies that are shaped like discs9. Using Hubble, astronomers had concluded that distant galaxies are more irregular in shape than nearby ones, which, like the Milky Way, often show 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; Webb’s first scientific insight was publicly revealed. Credit: NASA, ESA, CSA and STScI
“With the resolution of James Webb, we can see that galaxies have discs much earlier than we thought,” says Allison Kirkpatrick, an astronomer at the University of Kansas in Lawrence. This is a problem, he says, because it contradicts previous theories of galaxy evolution. “We’ll have to find out.”
Another preliminary manuscript suggests that massive galaxies formed in the Universe earlier than previously known. A team led by Ivo Labbé of Swinburne University of Technology in Melbourne, Australia, reports that seven massive galaxies have been found 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 very early in the history of the Universe,’ the scientists wrote.
And studies of galactic chemistry also show a rich and complicated picture emerging from the Webb data. An analysis of the first deep-field image examined the light emitted by galaxies at a redshift of 5 or more. (The 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 had thought that the process of chemical enrichment, in which stars fuse hydrogen and helium to form heavier elements, took a while, but the finding that it is underway in the first galaxies “will make us rethink the rate at which star formation occurs.” , says Kirkpatrick.
The nearest galaxies are smaller than expected.
Webb’s surprises continue even 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 maximum light was created.
Wren 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 infrared wavelengths detected by Webb, most massive galaxies appeared much smaller than Hubble images12. “It potentially changes our whole view of how galaxy sizes evolve over time,” says Suess. Hubble’s studies suggested that galaxies start small and grow over time, but Webb’s findings hint that Hubble didn’t have the whole picture, and so the evolution of galaxies might be more complicated than they had thought. scientists predicted.
With Webb just at the beginning of a projected 20 years of work, astronomers know they have a lot of changes ahead of them. “Right now I’m lying awake at three in the morning,” says Kirkpatrick, “wondering if everything I’ve ever done is wrong.”