Astronomers have uncovered striking new evidence that galactic winds, long suspected of shutting down star formation in massive galaxies, were already blowing fiercely just a billion years after the Big Bang.
Using resolved observations of both cold and ionized gas, researchers have identified a powerful supernova-driven outflow in a galaxy at redshift 5.3, when the Universe was only 1.1 billion years old. This marks the first time that scientists have directly observed winds blowing fiercely enough to quench star formation in such an early, massive system.
This outflow, probably driven by projected merger activity, is expelling gas at a two-to-one ratio relative to its generation. If continued, it could realistically blow all of the galaxy’s cool gas out within 100 million years = essentially dusting the cupboard where food is stored for new stars.
“Our results suggest that powerful merger-driven outflows may be a key mechanism to produce abundant massive quiescent galaxies in the early Universe when a large fraction of massive galaxies is interacting,” the team reports.
The most energetic outflows ever witnessed in the universe
The mass and energetics of this common, distant outflow have much in common with starburst-driven superwinds seen in more nearby galaxies. That kind of consistency points to something surprising: the efficiency of stellar feedback, or exploding stars acting to regulate galactic growth, may have changed relatively little over 12 billion years of cosmic history.
Galactic winds have long been considered a likely driver of rapid quenching, the process by which galaxies abruptly stop forming stars. But until now, direct evidence was lacking that early galaxies could generate winds powerful enough to matter. This new observation fills that gap, showing that even in the Universe’s infancy, massive galaxies were capable of blowing themselves dry.
Scientists wanted to see if galaxy winds have changed over time. They examined 99 examples of star-formation-driven outflows spanning 12 billion years. These winds were studied in ionized gas, which is the easiest to detect both nearby and far away.
They compared how much energy from starbursts pushes gas out of galaxies. The results show that the strength of these winds has remained roughly the same throughout cosmic history, even though galaxies themselves have changed significantly.
Chandra determined what causes a galaxy’s wind to blow
Computer models suggest that the type of gas carried away by winds can vary. But the key point is clear:
“Our analysis demonstrates that outflows strong enough to suppress, and potentially even quench significantly, star formation are present in rapidly assembling massive galaxies in the first billion years of the Universe.”
One galaxy, CRISTAL-02, is forming stars very quickly, 260 solar masses per year. Yet its wind is even stronger, blowing away 520 solar masses of gas per year. That’s about 20 times faster than typical galaxies at the same time. Evidence suggests a recent burst of star formation triggered this powerful wind.
Other studies with JWST show that black hole–driven winds (AGN outflows) can also shut down galaxies. Starburst winds, however, fade quickly once the young stars die, unlike AGN winds, which can last hundreds of millions of years.
The result also provides an explanation for a longstanding enigma of astrophysics, the population of massive quiescent galaxies present in the early universe. To the extent that merger-driven winds were a regular phenomenon, they could have turned star-forming giants into dormant behemoths in the blink of an eye, on a cosmic time scale, at any rate, so as to have accounted for a major portion of the galactic census every few hundred million years.
Journal Reference:
Rebecca Davies, D B Fisher, R Herrera-Camus et al. Multiphase images of a powerful supernova-driven wind in the early Universe. Monthly Notices of the Royal Astronomical Society. DOI: 10.1093/mnras/stag874