Using the James Webb Space Telescope (JWST), an international team of astronomers has captured a clear view of how a supermassive black hole sustains itself, bringing the field closer to solving a longstanding mystery in astrophysics.
Scientists from the University of Nottingham's School of Physics and Astronomy were part of the team led by led by the Université de Montréal who have published their findings today in The Astrophysical Journal Letters.
Nearly every large galaxy in the Universe has a supermassive black hole (SMBH) at its centre millions or even billions of times more massive than the Sun. When these black holes are actively pulling in surrounding material, they switch on like cosmic engines, blasting powerful jets of energy outward that can sculpt the entire galaxy around them, slowing down the birth of new stars and influencing how the galaxy grows over time. Astronomers call these types of black holes active galactic nuclei (AGN).
Despite extensive research, a puzzle has stumped scientists for years. If an AGN's jets heat up the surrounding gas, it should, in principle, shut off the black hole's food supply. So how does it keep feeding and growing?
The most plausible explanation is that the gas eventually cools back down, condenses into long thin streamers called filaments, and falls back toward the galaxy's centre. The SMBH feeds the process that feeds the SMBH; it is self-regulating. Despite decades of searching, directly observing how these filaments actually connect to the black hole has remained very difficult. That connection, a sort of missing link, is exactly what this new study reveals.
The team pointed JWST at galaxy NGC 4696, the central galaxy of the Centaurus Cluster, a dense group of galaxies located about 145 million light-years from Earth and one of the best laboratories for studying AGN mechanisms.
Previous images from the Hubble Space Telescope had shown a curious S-shaped swirl of gas near the galaxy's central black hole, but Hubble could only capture a snapshot of where the gas sat, not how it was moving.
With nearly 8 hours of observing time using JWST's NIRSpec instrument, the team produced detailed maps of the gas's motion deep inside the black hole's sphere of influence, at a resolution sharp enough to pick out features roughly 30 light-years — a tiny slice of a galaxy hundreds of thousands of light-years wide.
These maps showed that the S-shaped swirl is actually a spinning disk of gas wrapped around the SMBH, nearly 800 light-years across, with material whipping around at up to 600 kilometres per second. And critically, that disk appears physically connected to one of the large infalling filaments stretching outward into the galaxy. The observations showed gas flowing along the filament, pouring into the disk, and from the disk falling onto the SMBH.
"What JWST is revealing is that black holes may be the ultimate cosmic recyclers," says Julie Hlavacek-Larrondo, Professor at the Université de Montréal and lead author of the study. "They release enormous amounts of energy that heat their surroundings, yet that same gas can later cool into thin filaments that fall back inward and feed the black hole again. We are finally seeing this self-sustaining cycle in action."
The study helps astronomers paint a better picture of the full feeding cycle of a SMBH. Jets from the black hole pump energy into the galaxy's surrounding gas. That gas eventually cools, becomes unstable, and collapses into long filaments, some only a few hundred light-years wide but stretching thousands of light-years long. Magnetic forces bleed off the angular momentum of the gas as it falls, steering it inward. It accumulates into a spinning disk around the black hole. The disk feeds the black hole. The black hole fires its jets. And the cycle begins again.
JWST is now showing us the final link of this closed loop. The vast filamentary network of gas flows ultimately funnels gas down to a disk that fuels the black hole.
To test whether this explanation holds up, the team also ran state-of-the-art computer simulations of the system. The simulated gas behaved in a way that closely matched what JWST observed, lending strong independent support to the proposed picture.
A similar disk structure had previously been seen in another galaxy, NGC 1275 in the Perseus Cluster, using the ALMA Observatory. These new results in NGC 4696 suggest that this recycling mechanism may be common to massive galaxies across the Universe.
These findings have sparked a broad new observational effort for galaxy NGC 4696 and similar systems, with approved JWST programs and complementary campaigns using facilities such as the Very Large Telescope in Chile, the Very Long Baseline Array in New Mexico, and the Event Horizon Telescope, which took the very first image of a black hole in 2019. Altogether, these data will help improve our understanding of how black holes feed themselves and regulate galaxy growth across the Universe.
