Astronomers have uncovered a surprising rule that appears to determine when black holes unleash powerful jets of material into space. Even though black holes can differ in mass by millions of times, researchers found that they seem to follow the same fundamental pattern when producing these enormous cosmic outflows.
The discovery, published in Nature Astronomy, suggests that black holes can activate their jets at the same critical stage of their feeding cycle, whether they weigh roughly 10 times as much as the Sun or millions of times more.
The research was led by Dr. Adelle Goodwin, an astrophysicist at Curtin University’s International Centre of Radio Astronomy Research (ICRAR) and a Forrest Research Foundation Fellow, alongside co-author Dr. Andrew Mummery of the Institute for Advanced Study in Princeton.
The breakthrough emerged from years of studying unusual events in which supermassive black holes tear stars apart. By combining observations from telescopes in Australia, the United States, India, South Africa, and space, the scientists pieced together a clearer picture of how black holes behave as they consume matter.
Surprisingly, the crucial insight did not come while examining a telescope. It happened in a bar in Madrid, where Goodwin and Mummery were attending a scientific conference. During a conversation, they recognized that the same rule known to govern jet formation in relatively small black holes also seemed to apply to their supermassive counterparts.
Why Some Black Holes Erupt Years After Devouring Stars
One of the biggest mysteries the researchers wanted to explain was why black holes do not always launch jets at the same time.
When a supermassive black hole tears apart a star, it sometimes produces a powerful jet almost immediately. In other cases, the black hole appears relatively quiet for months or even years before suddenly producing a detectable radio outflow.
“We were looking at these events and asking why the timing was so different,” said Dr. Goodwin.
“Then the pattern became clear. The delayed jets were appearing when the black hole’s feeding rate dropped to the same critical point already known from much smaller black holes.
“That was the moment we realized this was not just a quirk of one type of black hole, but it looked like a rule that applied across the Universe.”
Although black holes are often portrayed as cosmic vacuum cleaners that swallow anything nearby, their feeding behavior is far more complicated.
As material spirals toward a black hole, not all of it necessarily disappears beyond the event horizon, the boundary past which nothing can escape. Some matter can instead be expelled into space through powerful jets and other outflows.
“When a black hole tears apart a star, it does not swallow everything neatly,” Dr. Goodwin said.
“Some of the material is consumed, and some is launched back into space in powerful jets and outflows.
“You can think of it as a black hole burp, except these burps can blast material across enormous distances and influence the galaxies around them.”
These enormous outflows can carry energy and matter far from the black hole, potentially affecting the surrounding galaxy.
How Scientists Studied Supermassive Black Holes in Action
Astronomers have long suspected that black holes operate according to the same underlying physical laws regardless of their mass. Demonstrating that connection, however, has been difficult.
One major obstacle is time. The feeding behavior of a supermassive black hole can change over thousands of years, making it nearly impossible for astronomers to watch an entire cycle unfold.
Goodwin and her colleagues tackled this problem by examining rare events known as tidal disruption events.
These occur when a star passes too close to a supermassive black hole and experiences such extreme gravitational forces that it is torn apart. Some of the resulting debris falls toward the black hole, temporarily increasing its feeding activity.
Unlike the much longer changes normally associated with supermassive black holes, these dramatic episodes can play out over just a few years. That gives scientists an unusual opportunity to track how a giant black hole responds as its supply of material changes.
The team initially examined 20 tidal disruption events using observations collected in visible light, ultraviolet, X-rays, and radio wavelengths. They then selected 10 events for which the available data allowed them to reliably estimate both the rate at which the black hole was consuming matter and the timing of its radio outflows.
By comparing these events, the researchers identified a remarkably consistent pattern.
A Universal 2% Rule for Black Hole Jets
The observations revealed two distinct stages during which black holes can produce jets.
The first occurs early in the feeding process, when the black hole is consuming matter at an exceptionally high rate.
The second can happen much later, hundreds or even thousands of days after the star is initially destroyed.
During this delayed phase, jets appear when the black hole’s feeding rate falls to approximately 2% of its Eddington limit.
The Eddington limit is a theoretical benchmark describing the point at which the outward pressure produced by radiation balances the inward pull of gravity. Astronomers use it to measure how intensely a black hole is feeding relative to a characteristic physical limit.
What makes the finding especially significant is that the same 2% threshold has already been linked to jet formation in much smaller black holes within our own Milky Way galaxy.
In other words, black holes separated by enormous differences in mass appear to activate delayed jets at essentially the same relative feeding rate.
“These black holes are separated by enormous differences in mass, but they appear to switch on their jets at the same point in the feeding process,” Dr. Goodwin said.
“That tells us something fundamental about black holes: the physics does not seem to care how big they are.”
The finding provides a potential explanation for an otherwise puzzling observation. Some black holes generate radio jets soon after destroying a star, while others appear inactive before producing powerful outflows much later.
Rather than behaving unpredictably, these delayed eruptions may be governed by a common physical threshold.
Predicting When Black Holes Will Launch Jets
Beyond revealing something fundamental about black hole physics, the discovery could help astronomers make much better use of powerful radio telescopes.
Observing time on major scientific facilities is limited and highly competitive. Researchers must carefully decide which objects to study, how frequently to observe them, and when they are most likely to reveal something important.
If astronomers can estimate when a black hole’s feeding rate will approach the critical threshold, they may be able to predict when a delayed jet is likely to appear.
“Radio telescopes are incredibly powerful, but knowing when to look is just as important as knowing where to look,” said Dr. Goodwin. “If we can anticipate when a black hole is more likely to launch a jet, we can run better targeted campaigns, waste fewer observations and improve our chances of catching these rare events at the moment they matter most.”
This could reduce unnecessary follow-up observations while increasing the chances of detecting rare jet-launching episodes at crucial moments.
The implications are particularly important for Western Australia, which will host the low-frequency component of the Square Kilometre Array Observatory (SKA), one of the largest and most ambitious radio astronomy projects ever undertaken.
The Australian Government has invested $387 million in the SKA, while the project’s total cost exceeds $2 billion. Making more efficient use of such an expensive facility could provide substantial benefits to astronomers and the wider scientific community, potentially allowing more important discoveries to be made with the available observing time.
As the next generation of astronomical surveys identifies growing numbers of tidal disruption events, researchers will face an increasingly difficult challenge in deciding which ones deserve closer attention.
The newly identified relationship between feeding rates and jet formation could provide a valuable guide, helping scientists focus their observations on the black holes most likely to produce detectable outflows.
A Black Hole Breakthrough Driven by Curiosity
Professor James Arvanitakis, Director of the Forrest Research Foundation, said the discovery highlights the importance of supporting early-career scientists who pursue ambitious questions without knowing in advance where the answers will lead.
This kind of open-ended investigation, often described as ‘blue sky’ research, can produce unexpected discoveries with benefits extending far beyond the original scientific question.
“The Forrest Research Foundation did not fund a predetermined answer, we backed an exceptional researcher with a difficult question,” Professor Arvanitakis said.
“That question has led to a discovery of international significance. This is exactly why fundamental research matters – it expands what we know, sharpens how we use major scientific infrastructure and builds capability that reaches well beyond astronomy.
“The fact this discovery was driven from Western Australia speaks to the strength of our research ecosystem, and the value of giving outstanding people a reason to build their careers here.”
By linking the behavior of relatively small black holes to that of supermassive giants, the findings strengthen the idea that the same basic physical processes operate across vastly different scales.
They also offer astronomers a more reliable way to anticipate one of the universe’s most dramatic phenomena: the moment a black hole begins launching a powerful jet into space.
