Astronomers have discovered a surprising pattern that could explain when black holes launch enormous jets of material into space. Despite having masses that differ by millions of times, black holes appear to follow the same fundamental rule when producing these powerful cosmic outflows.
The discovery, published in Nature Astronomy in 2026, suggests that some black holes launch delayed jets when their feeding rate falls to approximately 2% of a theoretical limit known as the Eddington limit. This finding could help scientists understand why certain black holes erupt soon after consuming a star, while others remain quiet for months or even years before producing detectable radio signals.
The research was led by Dr. Adelle Goodwin, an astrophysicist at Curtin University's International Centre for Radio Astronomy Research (ICRAR) and a Forrest Research Foundation Fellow, alongside Dr. Andrew Mummery of the Institute for Advanced Study in Princeton.
The findings provide new evidence that black holes of very different sizes may share the same underlying physical processes.
Why Do Some Black Holes Launch Jets Years Later?
Black holes are often described as objects that swallow everything that comes too close. However, their behaviour is more complex than this popular image suggests.
When matter approaches a black hole, it usually forms a rotating structure called an accretion disk. As the material moves inward, it heats up and releases enormous amounts of energy. Under certain conditions, some matter and energy can be directed outward in powerful jets that travel far into space.
These jets can carry energy across enormous distances and influence the environment surrounding a black hole, including the gas within its host galaxy.
One event that helps astronomers study this process occurs when a star passes too close to a supermassive black hole. The black hole's intense gravitational forces can tear the star apart in an event known as a tidal disruption event.
Some of the destroyed star's material falls toward the black hole, temporarily increasing its feeding rate.
However, scientists have observed that the resulting jets do not always appear at the same time. In some cases, powerful outflows emerge relatively quickly. In others, the black hole remains quiet for months or years before producing a detectable radio jet.
Dr. Goodwin and her colleagues wanted to understand why these delays occur.
Their investigation revealed that delayed jets tend to appear when the black hole's feeding rate drops to a particular level. Surprisingly, a similar threshold had already been associated with jet formation in much smaller black holes.
This suggested that the timing of these eruptions might not be random but controlled by a common physical rule.
The Surprising 2% Rule Behind Black Hole Jets
The key finding is that delayed jets appear when a black hole's feeding rate falls to approximately 2% of its Eddington limit.
The Eddington limit is a theoretical benchmark used to describe how intensely a black hole can accrete matter in relation to the balance between gravity and outward radiation pressure.
It provides astronomers with a useful way to compare the feeding activity of black holes of different sizes.
For example, a relatively small black hole with a mass around 10 times that of the Sun and a supermassive black hole containing millions of solar masses have enormously different physical scales. Their absolute feeding rates can also differ dramatically.
Yet, when their feeding rates are expressed relative to their respective Eddington limits, the same approximate 2% threshold appears to be important for jet formation.
This is what makes the discovery remarkable.
Rather than requiring a completely different explanation for small and supermassive black holes, the observations point toward a shared physical process operating across vastly different scales.
The researchers identified two periods when jets may emerge during a black hole's feeding cycle. One occurs early, when the black hole is consuming matter at an exceptionally high rate. The other can occur much later, as the feeding rate declines toward the critical threshold.
The 2% figure is therefore not a rule that every black hole must follow at all times. Instead, it describes an important condition associated with delayed jet formation in the events studied.
How Scientists Uncovered the Hidden Pattern
Studying supermassive black holes over their entire feeding cycles is extremely difficult because their activity can change over timescales much longer than a human lifetime.
Tidal disruption events offer a valuable opportunity to overcome this problem. Because these events can evolve over months or years, astronomers can observe changes in the black hole's feeding activity within a relatively short period.
The research team initially examined 20 tidal disruption events using observations collected across different parts of the electromagnetic spectrum, including visible light, ultraviolet radiation, X-rays and radio waves.
They then selected 10 events with sufficient data to estimate both the black holes' feeding rates and the timing of their radio outflows.
By comparing the observations, the scientists identified a consistent relationship between declining feeding rates and delayed jet formation.
The discovery also emerged from an unexpected conversation. Dr. Goodwin and Dr. Mummery were attending a scientific conference in Madrid when they recognised that a rule associated with smaller black holes could also explain the behaviour of their supermassive counterparts.
This connection helped turn observations of apparently different cosmic events into evidence for a potentially universal pattern.
Could Astronomers Predict the Next Black Hole Eruption?
One of the most important applications of this discovery could be improving predictions of when black holes are likely to launch jets.
Powerful radio telescopes can detect emissions from these outflows, but observing time on major facilities is limited. Scientists must carefully choose which objects to monitor and when to observe them.
If astronomers can estimate how quickly a black hole is consuming matter, they may be able to identify when its feeding rate is approaching the critical threshold.
This could help researchers schedule observations at the most promising times instead of repeatedly monitoring objects without knowing when a jet might appear.
Better predictions could also improve the chances of detecting rare jet-launching events and understanding how these outflows develop.
The finding may prove particularly useful as new astronomical surveys discover increasing numbers of tidal disruption events.
Why the Discovery Matters for Future Radio Telescopes
The research could also help astronomers make more efficient use of next-generation radio observatories, including the Square Kilometre Array Observatory (SKAO).
Australia is hosting the low-frequency component of this international radio astronomy project, which is designed to investigate some of the Universe's most important questions.
As astronomical surveys become more powerful, scientists will have more objects to study than they can observe in detail. A reliable way to identify when black holes are most likely to produce detectable jets could help researchers prioritise their targets.
However, the 2% relationship is not yet a perfect forecasting system. More observations will be needed to determine how consistently the threshold applies across different black holes and whether additional physical conditions influence jet formation.
A Universal Clue to Black Hole Behaviour
The discovery strengthens the idea that black holes of vastly different sizes can behave according to the same fundamental physical principles.
By identifying a common feeding-rate threshold associated with delayed jets, astronomers have found a possible explanation for why some black holes erupt long after consuming a star.
The research could eventually help scientists anticipate these powerful outflows, plan more effective telescope observations and better understand how black holes influence their surroundings.
For now, the finding offers an important clue to one of the Universe's most energetic phenomena: black holes may differ enormously in size, but the conditions that trigger their jets could follow a surprisingly universal rule.
Reference: Adelle J. Goodwin and Andrew Mummery, “A universal critical accretion rate for black hole jet formation,” Nature Astronomy (2026). DOI: 10.1038/s41550-026-02951-1.
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