Massimo Pascale did not plan to study the galaxy cluster SMACS 0723. But as soon as he saw the cluster glitter on the first image from the James Webb Space Telescope, or JWST, he and his colleagues could not help themselves.
“We thought we had to do something,” said Pascale, an astronomer at the University of California, Berkeley. “We can not stop ourselves from analyzing this data. It was so exciting.”
Pascale’s team is one of several groups of researchers who saw the first JWST images and immediately rolled up their sleeves. During the first days after the images and data used to create them were published, scientists have estimated the amount of mass the cluster contains, uncovering a violent incident in the cluster’s recent past and estimating the age of the stars in galaxies far beyond the cluster itself.
– We have been preparing for this for a long time. I myself have been preparing for years, and I am not very old, says Pascale, who is in his fourth year of graduate school. JWST “is really going to define a new generation of astronomers and a new generation of science as a whole.”
When the image of SMACS 0723 was released at a White House briefing on July 11, most of the focus was on extremely distant galaxies in the background (SN: 7/11/22). But in the center of the picture is SMACS 0723 itself, a much closer cluster of galaxies about 4.6 billion light-years from Earth. The mass bends the light from even further away, so that more distant objects look magnified, as if their light had traveled through the lens of another telescope of cosmic size.
The light from the most distant galaxy in this image began its journey to the JWST about 13.3 billion years ago – “almost at the beginning of the universe”, says astrophysicist Guillaume Mahler at Durham University in England, who already uses the image as his Zoom. background.
But the image can also fill in the history of the intermediate galaxy cluster itself. “People sometimes forget it – the galaxy cluster is also very important,” says Pascale.
Pascale’s and Mahler’s team started by making an overview of the distant galaxies that appear to be stretched and distorted in the image. The light from some of these galaxies is distorted so that multiple images of the same galaxy are displayed in different locations. Mapping these multifilament galaxies is a sensitive probe for the way the mass is spread around the cluster. It can again reveal where the cluster contains dark matter, the invisible, mysterious substance that makes up the majority of the mass in the universe (SN: 9/10/20).
Both teams found that SMACS 0723 is more elongated than it looked in previous observations. They also found a faint glow, called intracluster light, inside the cluster of stars that do not belong to any particular galaxy. Together, these features suggest that SMACS 0723 is still recovering from a relatively recent crash with another galaxy cluster, the teams report separately in a pair of papers sent to arXiv.org on July 14.
A galaxy cluster that has stood on its own for ages should have a rounder distribution of matter and intracluster light, instead of SMACS 0723’s elongated shape. The stars that emit intracluster light were probably torn from their home galaxies by gravitational forces during the collision.
“Two separate clusters have merged, and it seems to us that it is not completely settled yet,” says Pascale. “What we may be looking at is an ongoing merger.”
Mapping mass in the cluster is also important to decode the properties of the more distant galaxies in the background of the image, says Mahler. “You have to understand the cluster and its magnifying power to understand what’s behind it.”
Some scientists are already studying these distant galaxies in detail. The first JWST data includes not only beautiful images, but also spectra, measurements of how much light an object emits at different wavelengths. Spectra allow scientists to determine how much light a distant object has been stretched – or redshifted – by the expansion of the universe, which is a proxy for distance. Such data can also help reveal the composition of a galaxy and the age of the stars.
“The most important thing that limits the study of star formation in galaxies is the quality of the data,” said astrophysicist Adam Carnall at the University of Edinburgh. But with the vastly improved data from JWST, he says, he and his team were able to measure the age of stars in these distant galaxies.
Carnall and colleagues turned their attention to the spectra of distant galaxies just days after the SMACS image was released. They measured the redshifts of 10 galaxies, five of which were particularly distant, the team reports in an article sent to arXiv.org on July 18. One had already been highlighted as the most distant galaxy ever seen, with light emitted just 500 million years after the Big Bang 13.8 billion years ago. The other four shone as late as 1.1 billion years after the Big Bang.
All 10 galaxies were relatively young when they emitted light captured by JWST, Carnall said. They had all hit the star formation just a few million years earlier. It’s not particularly surprising, but it’s interesting.
“The ability to look at these small, weak galaxies … gives you a sense of what all galaxies must look like when they begin to form stars,” says Carnall.
Scientists hope to use JWST to find the first instances of star formation ever. Other early results suggest that they are already approaching.
Some galaxies in a JWST image of another cluster can be heard from an even earlier time, as early as 300 million years after the Big Bang, two research teams report in a couple of articles sent to arXiv.org on July 19. One of these galaxies appears to have already built up a spiral disk about a billion times the mass of the sun, which is surprisingly ripe for such an early galaxy.
And an overview of galaxies seen in the SMACS 0723 image suggests that galaxies with mature disks, rather than disorganized blobs or those consisting mainly of dark matter, may have been more common in the early universe than previously thought, reports another team in a arXiv.org paper submitted July 19th. This means that the early disks may not be out of date.
“Definitely these galaxies are a big deal, but it remains to be seen how exciting they will look in the context of a few months’ progress with JWST,” says Carnall. The best has not yet come.