Four Webb Telescope revelations about distant galaxies


Astronomers found these two distant galaxies in the same small patch of sky. They estimate that the one on the right dates 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 in spectacular fashion. In the two weeks since Webb’s first science images and data were made available to astronomers, they’ve reported a flood of preliminary findings, including multiple contenders for what may be the most distant galaxy ever seen. .

Webb’s images reveal a slew of glittering galaxies in the distant cosmos, appearing as they did just a few hundred million years after the Big Bang 13.8 billion years ago. That of the telescope amazingly sharp images shattered astronomers’ preconceived ideas about the early Universe.

“We had in mind an idea of ​​what the galaxies at these [distances] would look like and how much detail we would be able to see, but I think the reality is just a bit mind-boggling,” 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 expanding cosmos expands light to redder wavelengths, the telescope is well suited to spot galaxies that formed early in the history of the Universe. . In his early 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.

“It suggests what many of us have argued, 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 around 250 million years after the Big Bang, when the first stars formed and lit up the Universe. Later generations of stars amassed into galaxies, which are the faint red spots that Webb begins to discover.

Many Webb images are dotted with never-before-seen galaxies in the distant Universe. “There is hardly any empty space that has nothing,” Kartaltepe says.

One study combed through data from many distant galaxy fields that Webb has observed so far, to analyze the rate at which stars formed in the early Universe. He found 44 previously unknown galaxies dating back less than 300 million years to the Big Bang. Combined with 11 previously known galaxies, the results show that there was a large population of star-forming galaxies in the early Universe.1. The results “reaffirm the enormous potential for future [Webb] programs to transform our understanding of the young Universe,” wrote the team, led by Callum Donnan of the University of Edinburgh, UK, in a post on the arXiv preprint server.

Many galaxies are vying for the title of “farthest”.

Perhaps the most publicized rush is the rush of research teams vying to identify the most distant galaxy in the Webb data. A number of candidates have been spotted and will need to be confirmed by further studies, but all would break Hubble’s record for the most distant galaxy, which is around 400 million years after the Big Bang.2,3.

Pixelated image of the Maisie galaxy

Maisie Galaxy: Astronomer Steven Finkelstein named this distant galaxy after his daughter. He estimates that it dates from 280 million years after the Big Bang.Credit: 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 which included another galaxy slightly less distant 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 patch of sky. A second team also independently spotted the two galaxies5.

Astronomers characterize the distance of galaxies with a measure known as the redshift, which quantifies how far a galaxy’s light has been shifted to redder wavelengths; the higher the redshift, the further away 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 preprint server. arXiv. “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, with a redshift of 14, has emerged in a survey called CEERS, one of Webb’s most high-profile early projects. CEERS principal investigator Steven Finkelstein of the University of Texas at Austin dubbed the object Maisie’s Galaxy, after his daughter6. Another study looked at the very Webb’s first deep-field imagereleased 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 years after the Big Bangseven. And other arXiv papers speculate on other candidates, even up to redshifts of 208.

Some early galaxies are surprisingly complex.

The distant Webb galaxies also turn out to have more structure than astronomers had expected.

A study of Webb’s first deep-field image has revealed a surprisingly large number of distant disc-shaped galaxies9. Using Hubble, astronomers had concluded that distant galaxies are more irregularly shaped than nearby galaxies, which, like the Milky Way, often display regular shapes such as disks. 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.

First deep-field image from the James Webb Space Telescope

US President Joe Biden released this deep-field image on July 11 – the first publicly revealed scientific view of Webb.Credit: NASA, ESA, ASC and STScI

“With James Webb’s resolution, we are able to see that galaxies have disks much earlier than we thought,” says Allison Kirkpatrick, an astronomer at the University of Kansas at Lawrence. That’s a problem, she says, because it contradicts previous theories of galaxy evolution. “We’re going to 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 Labbé of Swinburne University of Technology in Melbourne, Australia, reports finding seven massive galaxies in the CEERS field, with redshifts between 7 and 10ten. “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 that the formation of massive galaxies began very early in the history of the Earth. Universe,” the scientists wrote.

And studies of galactic chemistry also show a rich and complicated picture emerging from 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 thought the process of chemical enrichment – in which stars fuse hydrogen and helium to form heavier elements – took a while, but the discovery that it is taking place in early galaxies “we will rethink the rate at which star formation occurs.” , says Kirkpatrick.

Nearer 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 “cosmic noon,” the time frame about 3 billion years after the Big Bang. This is when star formation peaked in the Universe and the most light was created.

Wren Suess, an astronomer at the University of California, Santa Cruz, compared Hubble images of galaxies at cosmic noon with Webb images of the same galaxies. At the infrared wavelengths detected by Webb, most massive galaxies appeared much smaller than in Hubble images12. “It potentially changes our whole view of how the size of galaxies changes over time,” says Suess. Hubble studies have suggested that galaxies start out small and get bigger over time, but Webb’s findings suggest Hubble didn’t have the big picture, and so galaxy evolution may be more complicated than scientists realize. had planned it.

With Webb just at the start of a planned 20+ year job, astronomers know they have a lot of changes ahead. “Right now, I find myself lying awake at three in the morning,” Kirkpatrick says, “wondering if everything I’ve ever done is wrong.”

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