🔭 Galaxies both young and dead, how is that possible?

In the early universe, some galaxies stopped forming stars barely one billion years after the Big Bang. How to explain this premature end? The key could lie in galactic winds of exceptional power, capable of stifling the birth of stars. That is what a recent study reveals.

The CRISTAL-02 system is a striking example. This galaxy merger, observed as it was 13 billion years ago, is ejecting colossal amounts of gas into space. The international team led by Rebecca Davies used JWST and the ALMA radio telescope to study this phenomenon.


This galactic wind is partly fueled by supernova explosions and intense radiation from the massive stars present. By dispersing cold molecular gas clouds, it prevents the formation of new stars. The CRISTAL-02 system thus loses more than 500 solar masses per year, twenty times more than similar galaxies. At this rate, the gas to form new stars runs out in barely one hundred million years, a blink of an eye on the cosmic scale.

In addition to what is produced by the stars present, in the case of CRISTAL-02, a supermassive black hole may have been active in the past and amplified this wind, even if it is not detected today.

This discovery adds an element to understanding the evolution of early galaxies. Nearly half of early massive galaxies are interacting with other galaxies. Cosmological simulations will need to incorporate these feedback mechanisms to better reproduce the observable universe. Stellar winds and black holes could thus explain why so many primordial galaxies seem to have lived fast and died young.

Our own Milky Way will experience a similar fate in 4.5 billion years, during its collision with Andromeda. This merger will likely trigger intense star formation, accompanied by powerful winds. The resulting system could then become a large, inert elliptical galaxy, like those observed by JWST.