An international team of astronomers, co-led by a scholar at the Institute for Advanced Study (IAS), has identified what appears to be a universal rule governing one of the most dramatic and enigmatic behaviors of black holes: the production of powerful, high-speed radio jets.
The researchers discovered that black holes are capable of launching these energetic jets at the exact same critical stage of their feeding cycle, regardless of their immense variation in size. This fundamental law applies uniformly to "stellar-mass" black holes, which typically weigh about ten times the mass of our sun, as well as to supermassive black holes that sit at the centers of galaxies and are millions or even billions of times heavier.
The groundbreaking work was carried out by Andrew Mummery, a Martin A. and Helen Chooljian Member for the 2025–2030 term in the School of Natural Sciences at the Institute for Advanced Study, alongside Adelle Goodwin, a Forrest Research Foundation Fellow at Curtin University’s International Centre of Radio Astronomy Research located in Western Australia.
Watching Black Holes Tear Stars Apart
Published in the scientific journal Nature Astronomy under the title "A universal critical accretion rate for black hole jet formation," the new study successfully brings together years of meticulous astronomical observations gathered across multiple wavelengths of light. To build their comprehensive dataset, the research team combined observations and archival information from a global network of telescopes situated in the United States, Australia, India, and South Africa, as well as space-based observatories.
The primary focus of their investigation centered on tidal disruption events—dramatic cosmic occurrences that happen when an unlucky star wanders just a bit too close to a supermassive black hole. The immense gravitational forces exerted by the black hole subject the star to severe tidal forces, ultimately ripping it apart into a long stream of gas and stellar debris. These rare and fleeting events provided the research team with a phenomenal, real-time opportunity to observe how a dormant black hole reacts and behaves after suddenly receiving a massive, unexpected supply of fresh stellar material.
"We really wanted to figure out this massive puzzle," explained Mummery, detailing the motivation behind the research. "Why do some supermassive black holes blast out radio jets right after shredding a star, while others just sit there looking completely dormant, only to suddenly fire up their jets months or even years later?"
Although black holes are frequently and colloquially compared to cosmic vacuum cleaners that quietly suck up everything in their path, their actual feeding behavior is considerably messier and far more violent.
"When a black hole tears apart a star, it does not swallow everything neatly," Goodwin stated, highlighting the chaotic nature of the feeding process.
While a portion of the shredded stellar material inevitably spirals inward and falls toward the event horizon of the black hole, a vast amount of the gas is violently expelled outward into surrounding space through powerful, high-velocity outflows. These enormous cosmic "burps" are capable of carrying matter and energy across vast distances of space, playing a critical role in shaping and significantly affecting the long-term evolution of the host galaxies that contain them.
A Faster Way to Study Supermassive Black Holes
For decades, astronomers have strongly suspected that black holes obey the exact same basic physical rules and equations, even when their respective masses differ by monumental scales. However, definitively proving this theoretical idea has proven exceptionally difficult in practice. This is primarily because astrophysical changes occurring around supermassive black holes normally unfold at a glacial pace, taking thousands or even millions of years to complete—far longer than human history.
Tidal disruption events uniquely offer a convenient way around this observational roadblock. When a passing star is completely destroyed by gravity, the resulting feeding episode and aftermath around a supermassive black hole can evolve, peak, and fade over the course of just a few years. That compressed timeline gives scientists a much faster, highly accelerated view of complex physical processes that would otherwise be virtually impossible to track and study in real time.
The key conceptual insight driving this new study actually emerged in a rather unexpected setting. During an astrophysics academic conference held in Madrid, Mummery and Goodwin were conversing in a local bar when they realized that the same specific physical rule already known to govern jet production in smaller, stellar-mass black holes might also apply directly to their supermassive counterparts.
Two Distinct Phases of Black Hole Jets
To rigorously test this intriguing hypothesis, the researchers examined a comprehensive sample of twenty tidal disruption events using multi-wavelength observations spanning optical light, ultraviolet light, X-rays, and radio waves.
After carefully filtering the data, they narrowed their sample down to ten exceptionally high-quality events for which they could reliably and accurately determine both the black hole’s fluctuating feeding rate and the precise timing of its associated radio outflows.
This detailed analysis revealed two separate, distinct periods during which powerful jets can form.
The first period occurs early in the sequence, while the black hole is furiously consuming stellar material at an extremely high, intense rate. The second period appears much later in the timeline—hundreds or even thousands of days after the star was initially torn apart by gravity.
At this much later stage, the black hole’s feeding rate drops significantly, falling to about two percent of its Eddington limit. The Eddington limit is the critical physical threshold at which the outward pressure of intense radiation perfectly balances the inward pull of gravity.
This specific two-percent threshold is especially important to astrophysicists because it is already well-known to trigger jet formation in much smaller, stellar-mass black holes residing within our own Milky Way galaxy. Finding that exact same threshold operating in massive supermassive black holes suggests that this fundamental aspect of black hole physics works in essentially the same way across an enormous, almost unimaginable range of masses.
Predicting When Black Holes Will Erupt
Beyond advancing fundamental astrophysical theory, this new discovery could also hold significant practical value for observational astronomers working with cutting-edge facilities.
If researchers can accurately predict when a distant black hole is likely to produce a delayed radio jet, they can schedule their telescope observations much more efficiently. This ability will substantially increase their chances of catching these relatively short-lived cosmic events precisely as they happen, maximizing scientific output.
That targeted approach could make much better use of heavily requested, oversubscribed telescopes around the world and dramatically reduce the number of observations wasted on periods when little to no activity is expected.
The capability to anticipate these sudden eruptions may become particularly useful for major upcoming astronomical facilities, including the massive Square Kilometre Array radio telescope project, which is currently scheduled to begin collecting its first official scientific data in 2028.
"We hope that our work will pave the way for even more profound discoveries about our universe," Mummery said.
