Galaxies die earlier than predicted

For a long time, it was considered certain in astronomy that galaxies formed new stars in the early days of the universe. However, in the data from the James Webb Space Telescope (JWST), researchers found a galaxy that stopped forming stars quite early on.

This galaxy stopped forming stars 700 million years after the Big Bang. During this time, a galaxy is "normally in full bloom", according to a statement from the University of Geneva. This indicates that the end of star formation occurred earlier than expected and predicted by the models. The study, which has been published in the Astrophysical Journal, was led at the University of Geneva.

Galaxies attract gas and grow

In the early universe, a galaxy attracts gas from its surroundings, which is then used to form new stars. As a result, the galaxy grows and attracts even more gas, which leads to the accelerated formation of more stars and thus to further growth of the galaxy.

However, star formation ends at some point. This is due to a process that astronomers call quenching. These galaxies are then referred to as quenched, dormant or "red and dead". They appear red because there are no longer any young, bright, blue stars in them, only older, smaller, red stars. The cause of quenching is not yet known.

The JWST discovered RUBIES-UDS-QG-z7, the most distant, i.e. oldest, massive quiescent galaxy (MQG). It has a spectroscopic redshift of 7.29, which corresponds to around 700 million years after the Big Bang. Normally, it takes a very long time for an MQG to form because it first has to form a large number of stars before star formation ends.

Star formation ended abruptly

With a size of around 650 light years, the galaxy is relatively small. In the first 600 million years after the Big Bang, it formed a stellar mass of more than 10 billion solar masses. It then abruptly stopped forming stars and became a dormant galaxy.

Advances in near-infrared spectroscopy allow astronomers to look further and further back into the history of the universe and discover older and older MQGs. The JWST has so far discovered some up to a time around 1.2 billion years after the Big Bang. On an astronomical scale, this is relatively soon after the Big Bang – the universe is around 13.8 billion years old. Now the even older one has been discovered.

JWST has already found several MQGs from this period. "The discovery of this galaxy, named RUBIES-UDS-QG-z7, implies that massive quiescent galaxies are more than 100 times more common in the first billion years of the universe than predicted by current models," says Andrea Weibel, first author of the study. The theoretical models that predict a longer formation time for such systems may need to be revised.

(wpl)