An international research team, co-led by a scholar at the Institute for Advanced Study (IAS), has uncovered what appears to be a fundamental rule governing one of the most powerful phenomena associated with black holes: the launching of high-speed jets.
The study reveals that black holes produce jets at a consistent critical point in their accretion cycle, irrespective of their mass. This applies equally to stellar-mass black holes, which are roughly ten times the mass of the Sun, and to supermassive black holes, which can be millions of times more massive.
The research was conducted by Andrew Mummery, Martin A. and Helen Chooljian Member (2025–30) in the School of Natural Sciences at the Institute for Advanced Study, together with Adelle Goodwin, a Forrest Research Foundation Fellow at Curtin University’s International Centre of Radio Astronomy Research in Western Australia.
Observing Black Holes Destroy Stars
Published in Nature Astronomy under the title “A universal critical accretion rate for black hole jet formation,” the study synthesizes years of multiwavelength observations. The researchers combined data from ground-based telescopes across the United States, Australia, India, and South Africa, as well as from space-based instruments.
Their primary focus was on tidal disruption events — occurrences in which a star strays too close to a supermassive black hole and is torn apart by extreme gravitational forces. These events provided the team with a rare window into how a black hole behaves after receiving a sudden influx of stellar material.
“We really wanted to solve this major puzzle,” said Mummery. “Why do some supermassive black holes emit radio jets immediately after shredding a star, while others appear entirely inactive, only to ignite their jets months or even years later?”
Black holes are often likened to cosmic vacuum cleaners, but their feeding processes are far more chaotic. “When a black hole disrupts a star, it does not consume everything in an orderly fashion,” Goodwin noted.
Some of the disrupted material spirals inward toward the black hole, while a significant portion is violently expelled into space through powerful outflows. These enormous cosmic outbursts can transport matter across immense distances and play a substantial role in shaping the evolution of their host galaxies.
A More Efficient Way to Study Supermassive Black Holes
Astronomers have long hypothesized that black holes adhere to the same fundamental physical laws regardless of their mass. Verifying this hypothesis has proven difficult, however, because activity around supermassive black holes typically unfolds over timescales of thousands to millions of years.
Tidal disruption events offer a solution to this challenge. When a star is destroyed, the resulting accretion episode around a supermassive black hole can evolve over just a few years, providing scientists with a dramatically accelerated view of processes that would otherwise be nearly impossible to observe in real time.
The key insight behind the new study emerged in an unexpected setting. During an astrophysics conference in Madrid, Mummery and Goodwin struck up a conversation in a bar and realized that the same rule known to control jet production in smaller black holes might also govern supermassive ones.
Two Distinct Phases of Black Hole Jet Activity
To test their hypothesis, the researchers analyzed twenty tidal disruption events using observations spanning optical, ultraviolet, X-ray, and radio wavelengths.
They ultimately narrowed their sample to ten high-quality events for which they could reliably measure both the black hole’s accretion rate and the timing of its radio outflows.
The analysis revealed two distinct windows in which jets can form.
The first occurs early, while the black hole is accreting material at an extremely high rate. The second arises much later — hundreds to thousands of days after the star was initially disrupted.
At this later stage, the black hole’s accretion rate drops to approximately two percent of its Eddington limit, the critical point at which the outward pressure of radiation balances the inward pull of gravity.
This two percent threshold is particularly significant because it is already recognized as the trigger for jet formation in much smaller black holes within our galaxy. Detecting the same threshold in supermassive black holes indicates that this aspect of black hole physics operates in a fundamentally consistent manner across a vast range of masses.
Predicting When Black Holes Will Erupt
The findings could also carry practical implications for observational astronomy.
If researchers can anticipate when a black hole is likely to produce a delayed jet, they can allocate telescope time more strategically and improve their chances of capturing these fleeting events as they occur.
This could lead to more efficient use of heavily demanded observatories and reduce unnecessary observations conducted during periods of minimal activity.
The ability to forecast such eruptions may prove especially valuable for upcoming major facilities, including the Square Kilometre Array radio telescope project, which is expected to begin collecting scientific data in 2028.
“We hope that our work will open the door to even more significant discoveries about our universe,” said Mummery.
