Since the James Webb Space Telescope became operational in 2022, numerous surprises have been revealed about what things looked like in the early stages of the universe. We can now 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 had spotted a galaxy where star formation had already stopped about 13.1 billion years ago, 700 million years after the Big Bang that gave rise to the universe. Many dead galaxies have been discovered over the years, but this was only about 500 million years ago at the earliest.
In some ways, this galaxy resembles the late Hollywood actor James Dean, famous for his “live fast, die young” life story.
“The galaxy seemed to have lived rapidly and intensely and then stopped forming stars very quickly,” said astrophysicist Tobias Looser of the University of Cambridge's Kavli Institute for Cosmology, lead author of the study published in the journal Nature.
'For the first few hundred million years of its history, the universe was violent and active, with plenty 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 million to a billion stars. That would put it close to the mass of the Small Magellanic Cloud dwarf galaxy, located near our Milky Way, although it is still forming new stars.
After a galaxy stops forming new stars, it becomes a bit like a star graveyard.
'Once star formation ends, existing stars die and are no longer replaced. This happens in a hierarchical manner, in order of their stellar weight, because the most massive stars are the hottest and shine the brightest, and as a result have the shortest lives,” Astrophysicist and Kavli Institute co-author Francesco D'Eugenio said.
“As the hottest stars die, the color of the galaxy changes from blue – the color of hot stars – to yellow to red – the color of the least massive stars,” D'Eugenio added. 'Stars with the mass of the Sun live about 10 billion years. If this galaxy stopped forming stars when we observed it, it would have no Sun-like stars today. But stars that are much less massive than the Sun can be. live for trillions of years, so they would continue to shine long after star formation stopped.”
The researchers determined that this galaxy experienced a burst of star formation that lasted 30 to 90 million years, after which it suddenly stopped. They're trying to figure 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” – bursts of energy from newly forming stars – that destroy the gas needed to form new stars. shapes, have been pushed out of the Milky Way.
“Alternatively, gas can be consumed very quickly by star formation, without being immediately replenished with fresh gas from the galaxy's surroundings, resulting in starvation of galaxies,” Looser said.
NASA's Webb can see greater distances, and therefore further back in time, than its predecessor Hubble Space Telescope. Among other discoveries, Webb has enabled astronomers to see the earliest 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's possible, they said, that it resumed star formation later.
“Some galaxies can undergo a rejuvenation if they can find fresh gas that they can convert into new stars,” says D'Eugenio. “We don't know the ultimate fate of this galaxy. This may depend on the mechanism that stopped star formation.”
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