James Webb captures the oldest dead galaxy – 03/06/2024 – Science

Since coming into operation in 2022, the James Webb telescope has led to a series of discoveries about the early stages of the Universe. Now, one more can be added to this list: a galaxy that was already dead when the Universe was just 5% of its current age.

This Wednesday (6), scientists said that the telescope spotted a galaxy where star formation had already ceased around 13.1 billion years ago, 700 million years after the Big Bang. Many dead galaxies have been detected over the years, but this is the oldest by about 500 million years.

“This galaxy appears 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 published in the journal Nature.

“For the first 100 million years of its history, the Universe was violent and active, with plenty of gas around to fuel star formation in galaxies. This makes this discovery particularly intriguing and interesting,” Looser added.

The newly discovered galaxy is relatively small, with perhaps 100 million to 1 billion stars. This would place it in the mass neighborhood 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 stellar graveyard.

“Once star formation ends, existing stars die and are not replaced. This happens in a hierarchical fashion, in order of stellar weight, because the most massive stars are the hottest and shine the brightest, and as a result have longer lifetimes. 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 for about 10 billion years. If this galaxy stopped forming stars at the time we observed it, there would be no Sun-like stars left in it today. However, stars much less massive than the Sun can live trillions of years, so they would continue to shine long after star formation has stopped.”

In the researchers’ assessment, this galaxy went through a burst of star formation that lasted 30 to 90 million years, and then suddenly stopped. They trying to figure out why.

It could be, they said, due to the action of a supermassive black hole at the galactic center or to a phenomenon called “feedback” — bursts of energy from newly formed stars — that pushed the gas needed to form new stars out of the galaxy.

“Alternatively, the gas could be consumed very quickly by star formation, without being readily replenished by fresh gas from the surrounding galaxy, resulting in galactic starvation,” Looser said.

James Webb is capable of looking at greater distances, and thus further back in time, than its predecessor, Hubble. Among other discoveries, the telescope allowed astronomers to see the oldest known galaxies, which turned out to be larger and more numerous than expected.

In the new study, researchers were able to observe the dead galaxy at one moment in time. It’s possible, they said, that it resumed star formation later.

“Some galaxies may undergo rejuvenation if they can find fresh gas to convert into new stars,” said D’Eugenio. “We don’t know the ultimate fate of this galaxy. It may depend on the mechanism that caused star formation to stop.”