In a cosmological confrontation of “Are they or aren’t they?” the contest is firmly in favor of first – 10 to one, at last count. The question is of paramount importance: are the galaxies that the James Webb Space Telescope (JWST) sees in the early universe really as surprisingly distant as we think? So far, the answer is a resounding yes. “The vast majority of these galaxies are being confirmed,” says Steven Finkelstein, an astronomer at the University of Texas at Austin. “That means whatever we saw last summer, that maybe the universe was very good at forming stars very early on, is going to hold.”
The summer of 2022 has seen the JWST unleash a torrent of discoveries. After a December 2021 launch and more than six months in service, JWST fully ignited in July 2022. Almost immediately after, its unprecedented infrared sensitivity revealed the faint glows of galaxies seemingly from the distant universe that n had formed only hundreds of millions of years after the big bang. Astronomers expected these landmark results to appear more gradually. “There was a data explosion,” says Finkelstein.
These early results came so quickly because the researchers used a clever shortcut to estimate galactic distances. Astronomers typically determine cosmic coordinates by precisely measuring the redshift, a stretching of a galaxy’s light toward the red end of the electromagnetic spectrum as a result of the universe’s expansion. But it requires the act of assembling and analyzing a galaxy’s spectrum, a time-consuming and subtle process known as spectroscopy. Instead, JWST’s discovery firehose was fueled by cruder, faster photometry-based techniques that essentially use obvious variations in the brightness of galaxies to estimate their redshift.
So while the photometric results came in droves last summer, the spectroscopic results are only just beginning to trickle in. Already, however, with spectra-based distances in hand for only a dozen candidates, the researchers find that most measurements match early photometric results. The latest, published in natural astronomy last week confirmed earlier distance estimates for four other galaxies identified by the JWST Advanced Deep Extragalactic Survey (JADES). “We’ve been waiting for this for decades,” says Emma Curtis-Lake of the University of Hertfordshire in England, who led the study of the spectroscopic results. “To be able to do that in the first few months of this telescope was just amazing.”
Of the four, the furthest away is the one with the somewhat convoluted name JADES-GS-z13-0. It has a redshift value of 13.2, meaning we see the galaxy as it appeared just 320 million years after the big bang. This high redshift makes JADES-GS-z13-0 the furthest currently known in the universe – a record that JWST looks set to break again imminently, but shows why astronomers are so excited . We now know for sure that we are probing an era in the universe that no human has ever laid eyes on before. “It’s amazing,” says Pieter van Dokkum of Yale University. This galaxy, he evocatively notes, is only slightly older from our perspective than the total length of existence of sharks on Earth – about 300 million years. “You go from nothing to these fully formed galaxies in the blink of an eye,” says van Dokkum.
However, not all high redshift candidate galaxies were so lucky, highlighting the early caution of astronomers. In July, another survey called the Cosmic Evolution Early Release Science Survey (CEERS), led by Finkelstein, spotted a possible galaxy at a redshift of 16.4, just 240 million years after the big bang. Subsequent spectroscopy showed that the inference was wrong, as revealed in late March by research led by Pablo Arrabal Haro, an astronomer at the National Science Foundation’s NOIRLab. The galaxy is actually a dusty impostor located at a redshift of 4.9, a still impressive but not at all record-breaking redshift of 1.2 billion years after the big bang. High levels of star formation are thought to have clouded early photometric analyses. “We can easily be fooled by contamination,” says Callum Donnan of the University of Edinburgh in Scotland, co-author of the book. “A high redshift galaxy can be mimicked by a lower redshift galaxy with different characteristics.”
The good news is that this particular galaxy appears to be a “unique case,” says Donnan. The same study was able to confirm that two other candidate galaxies did not have the same problem. One of them is the Maisie galaxy, which is seen at a redshift of 11.4, about 400 million years after the big bang, and is named after Finkelstein’s daughter. “She was very excited when I told her it was real,” Finkelstein says.
Now that such galaxies are confirmed, their scientific implications can be explored in more detail. These galaxies are small, several times smaller than the Milky Way. But some appear extremely bright and massive and have high star formation rates similar to our galaxy, which forms about one new star every year. Although galaxies do not yet pose problems for major models of cosmology, they do suggest that galactic formation began earlier and proceeded faster than expected in the universe, which theorists had previously predicted. snap.
“We are seeing massive galaxies rise faster than we previously thought,” says Fabio Pacucci of the Harvard-Smithsonian Center for Astrophysics. The age of some of these first galaxies is estimated at a few tens of millions of years. This could have implications for the large structures of dark matter known as halos that sculpted early galaxies and for the nature of dark matter particles themselves. “One of the big open questions is: East dark matter?” says Sandro Tacchella of the University of Cambridge. “The first generation of galaxies are a sensitive probe for different models of dark matter.”
Some problematic – and potentially pattern-destroying – early universe candidate galaxies still remain. The first of these could be a class of galaxies identified by Ivo Labbé of Swinburne University of Technology in Australia and his colleagues. The team found galaxies with billions of solar masses, comparable in weight to the Milky Way, from around 750 million years after the big bang. These galaxies are 10 to 100 times larger than galaxies previously observed at this time and are packed into structures 30 times smaller than the Milky Way. “They’re small, but they’re massive,” says Labbé, who says JWST continues to find similar galaxies basically anywhere they look deep into the sky. So far, the galaxies have only been studied photometrically, with a spectroscopic analysis scheduled for July. But the photometric success of other JWST results so far suggests the preliminary analysis by Labbé and colleagues is correct. “The more extreme galaxies out there always seem to be a problem,” says Michael Boylan-Kolchin of the University of Texas at Austin, who was not involved in the JWST observations discussed in this paper. “Some of these systems are expected to form stars 1,000 times faster than the Milky Way. The question is: is this an incredibly high amount of star formation?”
The field continues to change rapidly. An ongoing investigation called COSMOS-Webb should provide many more high redshift candidates. “Our estimates in the proposal were [to find galaxies] down to a redshift of about 10,” says Jeyhan Kartaltepe of the Rochester Institute of Technology, who leads the program. “But those numbers might have been too pessimistic.” Many other astronomers have submitted requests for additional free time on the telescope to the Space Telescope Science Institute in Maryland, which operates the observatory. Still others have submitted proposals for the telescope’s second year of scheduled science observations, called Cycle 2, which begins in July.
Some fear that the terrain is changing too quickly. While much of JWST’s data, about 80%, has an exclusive 12-month window during which responsible researchers have exclusive access to their own observations, the rest is open access. This means that when observations are taken, they are immediately available to the public, and anyone can use them. Before Arrabal Haro and his colleagues published their analysis of the redshift 16.4 galaxy on the arXiv.org preprint server in late March, their open-access work had already been picked up by astronomers on Twitter. “I just wanted to do an extremely simple test,” says Gabriel Brammer of the University of Copenhagen, who posted some early results. “The team did a much more detailed analysis. But you can see it instantly if you know where to look.
Not everyone is happy with such easy access. “You have postdocs who have spent years of their lives working on this and making these observations possible,” says Rebecca Larson of UT Austin, co-author of the Arrabal Haro paper and fellow of the CEERS team. “Then our data comes out, and it’s public, and people race us for the results. We are working on it and we are also asked to provide other contributions to the community. Then other people will come in and post papers. It’s really frustrating to see what’s going on. It is unclear how to resolve the tensions at this time. “It would be better if there were more concrete rules,” says Tom Bakx of Nagoya University in Japan, who was not involved in the research. “Imagine if you have young children, it’s just not possible to spend the whole night calibrating the data. There is a small power imbalance. It’s a very open competition.
More positively, things seem to have cooled off somewhat since JWST’s first frantic weeks of operation. Today, astronomers are doing what they’ve long dreamed of: getting their first definite glimpses of a time in the universe never studied before. Who knows how long we’ll see. “Perhaps galaxy formation already began at a redshift of 20,” van Dokkum says, referring to a time just 180 million years after the big bang, a barely unfathomable time before JWST. . If the telescope shows us something, it’s because we should expect the unexpected.
Editor’s Note (4/14/23): This article was edited after it was published to correct Pablo Arrabal Haro’s last name and comparison to the total lifespan of sharks on Earth.
