Astronomers have found a galaxy that stopped producing stars over 13 billion years ago, making it the earliest "dead" galaxy ever detected.
The discovery was made using the James Webb Space Telescope by a global team led by the University of Cambridge. They found this inactive galaxy when the universe was merely 700 million years old.
This galaxy seems to have lived fast and died young: It experienced a rapid burst of star formation that ceased almost as abruptly, a phenomenon not expected so early in the cosmos's history. The reasons behind its sudden inactivity remain a mystery.
Insights into Early Universe Dynamics
Published in Nature, this research could shed light on the processes that halt star formation in galaxies and whether these processes have evolved over billions of years.
"The first few hundred million years of the universe was a very active phase, with lots of gas clouds collapsing to form new stars," said Tobias Looser of the Kavli Institute for Cosmology, the study's lead author. "Galaxies need a rich supply of gas to form new stars, and the early universe was like an all-you-can-eat buffet."
"It's only later in the universe that we start to see galaxies stop forming stars, whether that's due to a black hole or something else," added Dr Francesco D'Eugenio, also from the Kavli Institute.
Astronomers suggest that star formation within galaxies can halt due to various reasons, leading to a shortage of the gas needed for creating new stars. Factors such as a supermassive black hole or the effects of star formation itself might eject gas, abruptly stopping new star production. Alternatively, rapid star creation could deplete gas reserves without timely replenishment, causing galaxy starvation.
"We're not sure if any of those scenarios can explain what we've now seen with Webb," stated co-author Professor Roberto Maiolino. "But now that we can see so much further back in time, and observe that the star formation was quenched so rapidly in this galaxy, models based on the modern universe may need to be revisited."
Through data from the JWST Advanced Deep Extragalactic Survey (JADES), researchers discovered this galaxy had a short, intense star formation period lasting between 30 and 90 million years, which unexpectedly stopped 10 to 20 million years before its observation by the Webb telescope.
Challenging Previous Notions and Future Exploration
"Everything seems to happen faster and more dramatically in the early universe, and that might include galaxies moving from a star-forming phase to dormant or quenched," Looser explained.
This particular galaxy, observed to be inactive, is the oldest of its kind discovered so far, existing just 700 million years after the big bang, over 13 billion years ago. This makes it a groundbreaking find by the Webb telescope.
Not only is this galaxy one of the oldest, but it's also on the smaller side, similar in mass to the Small Magellanic Cloud (SMC), a nearby dwarf galaxy that is still actively creating new stars. Compared to other inactive galaxies from the early universe, which were typically much larger, this discovery shows how Webb's enhanced sensitivity can uncover smaller, dimmer galaxies.
Despite appearing inactive when observed, there's a possibility that this galaxy might have reignited star formation in the 13 billion years since it was first spotted.
"We're looking for other galaxies like this one in the early universe, which will help us place some constraints on how and why galaxies stop forming new stars," said D'Eugenio. "It could be the case that galaxies in the early universe 'die' and then burst back to life -- we'll need more observations to help us figure that out."
This study received support from the European Research Council, the Royal Society, and the Science and Technology Facilities Council (STFC), under UK Research and Innovation (UKRI).
