Cosmos
Cosmos is a quarterly science magazine. We aim to inspire curiosity in ‘The Science of Everything’ and make the world of science accessible to everyone.
By Cosmos
A new study using observations from the James Webb Space Telescope (JWST) suggests that supermassive black holes are rapidly shutting off star formation in massive galaxies.
The black holes do this by explosively removing large amounts of gas that would otherwise be used in the accretion of matter to form new stars. The research is published in Nature.
Supermassive black holes are between 100,000 and 10 billion times the size of our Sun. These cosmic behemoths are usually found at the centres of galaxies where they consume massive amounts of gas. Galaxies in which this process is taking place are said to have “active galactic nuclei” (AGN).
It’s long been thought that outflows from supermassive black holes can suppress star formation. But direct observational evidence for this has been lacking until now.
How can a black hole have an outflow in the first place? It’s a fair question given that black holes are meant to be so dense that their gravitational field can prevent even light from escaping.
Scientists aren’t completely sure, but the best theories suggest that spinning black holes have this outward flow of matter, in the form of vertical jets of material, to conserve angular momentum.
Much of the difficulty in proving that this wind is suppressing star formation is because previous studies have been limited to studying ionised gases, which are warm, in the black hole outflows. But the new study shows that more than 90% of the wind is made up of cool neutral gas – effectively invisible in previous research.
“The JWST made it possible for us to observe the cooler, neutral gas phase of normal AGN-driven outflows in distant galaxies,” says corresponding author Dr Rebecca Davies from Melbourne’s Swinburne University.
Subject of the research was COSMOS-11142 – a massive, 4,000-light-year-across galaxy about 11 billion light-years from Earth.
“In the galaxy studied, we found that the outflow rate in the neutral phase was ~100 times larger than the outflow rate in the ionised phase, therefore revealing a lot of outflowing mass that was previously invisible.”
The team was able to see for the first time how supermassive black hole outflows push star-forming gas away.
“The outflow is removing gas faster than gas is being converted into stars, indicating that the outflow is likely to have a very significant impact on the evolution of the galaxy,” Davies explains. “Our findings provide new evidence to indicate that black-hole driven outflows are able to rapidly shut-off or ‘quench’ star-formation in massive galaxies.”
Quenching star formation is a fundamental process in the life cycle of galaxies. It represents the transition from a galaxy which is forming stars – and, therefore, able to grow and change – and a galaxy which is static.
This quenching is still poorly understood by astronomers. The new research is an important insight into this process.
