Astronomers have observed what is currently the oldest known “dead” galaxy, thanks to the James Webb Space Telescope.
The discovery by the University of Cambridge reveals a galaxy that stopped forming stars more than 13 billion years ago, when the universe was barely 700 million years old.
“A galaxy is dead when it no longer forms stars,” the study's co-author Dr Francesco D’Eugenio told The National.
“This is the earliest example known of a dead galaxy millions of years ago, when the universe was very young and cold gas [from which stars are born] was abundant in and around galaxies”.
“It is surprising to see a galaxy that is not forming stars, during an epoch when other galaxies were bursting with star formation.”
The study, detailed in Nature, explored how star formation ceases and the effects on galaxy evolution.
This discovery not only challenges previous models based on the modern universe but also opens new avenues for understanding the early universe's complexities.
The researchers found this celestial anomaly in a tiny fraction of the Goods South Field, highlighting it in a false-colour JWST image.
The galaxy in question appears to have undergone a brief but intense phase of star formation before abruptly going quiet.
“The first few hundred million years of the universe were a very active phase, with lots of gas clouds collapsing to form new stars,” said lead author Tobias Looser, from the Kavli Institute for Cosmology at the University of Cambridge.
Theories abound as to why star formation ceases in galaxies, ranging from the influence of supermassive black holes to the rapid consumption of gas necessary for creating new stars.
“Stoppage of star formation is a crucial stage of galaxy evolution; in addition, understanding when and how galaxies stop forming stars is a crucial step towards understanding how star formation and supermassive black hole accretion work,” Dr D’Eugenio said.
However, this particular galaxy's early and abrupt transition to dormancy is unique, suggesting that models based on more recent periods in the universe's history may need re-evaluation.
“We’re not sure if any of those scenarios can explain what we’ve now seen with Webb,” said co-author Roberto Maiolino, professor of experimental astrophysics at the Kavli Institute for Cosmology.
This ancient galaxy's discovery was made possible by the JWST Advanced Deep Extragalactic Survey (Jades), which revealed that its star-forming period lasted between 30 million and 90 million years before halting suddenly 10 million to 20 million years before its observation by the JWST.
“We simply did not expect to find dead galaxies so early; this means that our theories – which are rooted in observations of the nearby universe – do not quite capture the higher energy of processes in the early Universe,” Dr D’Eugenio said.
Despite its current “dead” status, astronomers do not discount the possibility that the galaxy could have reignited its star-forming engine in the billions of years since it was last observed.
“All the things that enable us to exist – the oxygen and nitrogen in the air we breath, the carbon in our food and fuel, the iron in our tools, the calcium in our bones – all these elements were synthesised in the core of stars,” Dr D'Eugenio said.
“I find it incredibly uniting to think that the matter that makes you and I, once, may have been in the core of the same star. Studying the earliest galaxies is a bit [like] studying our common origins”.
The search is now on for more galaxies from the early universe to better understand the mechanisms behind the cessation of star formation, which could reveal that galaxies might “die” and then spring back to life, adding a new layer of complexity to our cosmic understanding.
