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A false color image obtained by the James Webb Space Telescope (JWST) shows the galaxy JADES-GS-z7-01-QU, the oldest known “dead” galaxy in the universe, a galaxy that has stopped star formation, in this undated pamphlet. Image obtained by Reuters. | Photo credit: Reuters
Since becoming operational in 2022, the James Webb Space Telescope has uncovered numerous surprises about what things were like in the early stages of the universe. Now we can add one more: observations of a galaxy that was already “dead” when the universe was only 5% of its current age.
Scientists said Wednesday that Webb has discovered a galaxy where star formation had already ceased about 13.1 billion years ago, 700 million years after the Big Bang that gave rise to the universe. Many dead galaxies have been detected over the years, but this is the oldest, about 500 million years ago.
In some ways, this galaxy is like that of the late Hollywood actor James Dean, famous for his “live fast, die young” life story.
“The galaxy seemed to have lived quickly and intensely, and then stopped forming stars very quickly,” said astrophysicist Tobias Looser of the Kavli Institute of Cosmology at the University of Cambridge, lead author of the study. study published in the magazine Nature.
“In the first few hundred million years of its history, the universe was violent and active, with a lot of gas around to fuel star formation in galaxies. That makes this discovery particularly puzzling and interesting,” Looser added.
This galaxy is relatively small, with perhaps 100 to 1 billion stars. That would put it in the vicinity of the mass of the Small Magellanic Cloud dwarf galaxy located near our Milky Way, although it is still forming new stars.
When a galaxy stops forming new stars, it becomes a bit like a stellar graveyard.
“Once star formation ends, existing stars die and are not replaced. This happens hierarchically, in order of stellar weight, because the most massive stars are the hottest and brightest, and as a result they have the longest lives.” short.” said Kavli Institute astrophysicist and study co-author Francesco D’Eugenio.
“As the hottest stars die, the color of the galaxy changes from blue (the color of hot stars) to yellow and red (the color of less massive stars”), D’Eugenio added. “Stars with a mass similar to the Sun live about 10 billion years. If this galaxy stopped forming stars at the time we observed it, there would be no stars similar to the Sun left in it today. However, stars may exist “Much less massive than the Sun. They will live for billions of years, so they will continue to shine long after star formation stops.”
The researchers determined that this galaxy experienced a burst of star formation that lasted between 30 and 90 million years and then suddenly stopped. They are trying to find out why.
It could be due, they said, to the action of a supermassive black hole at the galactic center or to a phenomenon called “feedback” (energy bursts from newly formed stars) that expelled the gas needed to form new stars out of the galaxy.
“Alternatively, gas may be consumed very quickly during star formation, without being quickly replenished by fresh gas from the galaxy’s surroundings, resulting in starvation of the galaxy,” Looser said.
NASA’s Webb is capable of observing greater distances and therefore further back in time than its predecessor, the Hubble Space Telescope. Among other discoveries, Webb has allowed astronomers to see the oldest known galaxies, which turned out to be larger and more abundant than expected.
In the new study, the researchers were able to observe the dead galaxy at one point in time. It is possible, they said, that star formation subsequently resumed.
“Some galaxies may experience rejuvenation if they can find fresh gas to turn into new stars,” D’Eugenio said. “We do not know the final fate of this galaxy. This may depend on what mechanism caused star formation to stop.”