Mar 7 2024Reviewed by Lexie Corner
An international team of astronomers led by the University of Cambridge has discovered the oldest known “dead” galaxy, which dates back to when the universe was only 700 million years old, using the James Webb Space Telescope.
This galaxy seems to have lived a short life and died young: star formation occurred swiftly and abruptly, which is unusual for a galaxy that has formed so early in its history. It is unknown what caused this galaxy to stop producing new stars and whether its “quenched” state is transitory or permanent.
The findings, published in the journal Nature, may be crucial in assisting astronomers in their quest to comprehend the processes and reasons behind galaxies’ cessation of star formation, as well as whether or not 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. Galaxies need a rich supply of gas to form new stars, and the early universe was like an all-you-can-eat buffet.
Tobias Looser, Study First Author, Kavli Institute for Cosmology, University of Cambridge
Dr. Francesco D’Eugenio, study co-author, from the Kavli Institute for Cosmology, added, “It is 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.”
A galaxy can become starved of the gas necessary for the formation of new stars due to a variety of factors that astronomers believe can slow down or stop star formation. Star formation may cease abruptly due to internal factors that force the gas out of the galaxy, such as a supermassive black hole or feedback from star formation. On the other hand, gas may be rapidly used up by star formation and not quickly replaced by new gas from the galaxy’s surroundings, leading to starvation in the galaxy.
We are not sure if any of those scenarios can explain what we have now seen with Webb. Until now, to understand the early universe, we’ve used models based on the modern universe. 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.
Roberto Maiolino, Study Co-Author and Professor, Kavli Institute for Cosmology, University of Cambridge
The astronomers concluded that this galaxy underwent a brief but intense period of star formation over a period between 30 and 90 million years using data from JADES (JWST Advanced Deep Extragalactic Survey). However, star formation abruptly ceased between 10 and 20 million years before the time it was detected by Webb.
Looser added, “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.”
Although dead galaxies in the early universe have been seen by astronomers before, this galaxy is the oldest–it was formed only 700 million years after the Big Bang, or more than 13 billion years ago. This is one of Webb’s most in-depth observations to date.
Not only is this galaxy the oldest, but it also has a low mass, comparable to that of the nearby dwarf galaxy Small Magellanic Cloud (SMC), which is still forming new stars. Larger quenched galaxies have been observed in the early universe, but Webb’s enhanced sensitivity makes it possible to observe and analyze smaller and fainter galaxies.
Although it looks dead at the time of observation, astronomers speculate that this galaxy may have revived and begun to form new stars in the approximately 13 billion years since.
D’Eugenio added, “We are 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. It could be the case that galaxies in the early universe ‘die’ and then burst back to life–we will need more observations to help us figure that out.”
The Science and Technology Facilities Council (STFC), a division of UK Research and Innovation, the Royal Society, and the European Research Council provided partial funding for the study.
Journal Reference:
Looser, JT. et al., (2024) A recently quenched galaxy 700 million years after the Big Bang. Nature. doi:10.1038/s41586-024-07227-025
Source: https://www.cam.ac.uk/