The discovery, accepted for publication in the prestigious journal Nature Astronomy, shows that black holes appear to switch on their powerful jets at the same critical point in their feeding cycle, regardless of their mass. The work 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, together with co-author Dr Andrew Mummery of the Institute for Advanced Study in Princeton. Their finding emerged from years of painstaking work piecing together observations from telescopes across Australia, America, India and South Africa, as well as instruments in space, all trained on rare and dramatic events in which stars are torn apart by supermassive black holes.

The central question that drove the research was deceptively simple: why do some black holes produce radio jets soon after ripping a star apart, while others seem to stay silent for months or even years before suddenly lighting up? For astronomers monitoring the sky, the inconsistency was frustrating. A tidal disruption event — the technical term for a star being shredded by a supermassive black hole — can flare brilliantly in optical, ultraviolet and X-ray light, yet the radio signature of a jet may arrive on a schedule that seems arbitrary from event to event. Without a predictive rule, telescope time was being spent largely on guesswork.

The breakthrough, Dr Goodwin recalls, did not happen at a telescope console but in a bar in Madrid during a conference, where she and Dr Mummery realised that the same jet-launching rule already known from small black holes in our own Galaxy also appeared to hold for supermassive ones. ‘We were looking at these events and asking why the timing was so different,’ Dr Goodwin said. ‘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 realised this was not just a quirk of one type of black hole, but it looked like a rule that applied across the Universe.’

Proving that black holes of wildly different masses share the same basic physics has long been one of the field’s stubborn challenges. The reason is time: supermassive black holes, sitting at the centres of galaxies with millions to billions of solar masses, normally evolve over thousands of years or longer. Watching one complete a full feeding cycle is simply impossible within a human career, let alone a single observing campaign. Stellar-mass black holes, by contrast, feed and flare on timescales of days to months, which is why much of what astronomers know about accretion and jet formation comes from these smaller objects in our Galaxy.

Dr Goodwin found a way around the timescale problem by exploiting tidal disruption events. When a star strays too close to a supermassive black hole, the immense tidal forces rip it apart, and the resulting debris forms a hot, swirling accretion disc as it spirals inward. Crucially, this compresses an entire supermassive black hole feeding episode into a few years rather than several millennia, giving astronomers a rare chance to watch the full process — from the initial stellar destruction to the late-time launch of jets — unfold in something close to real time.

To turn these fleeting events into a rigorous test, the researchers analysed twenty tidal disruption events using optical, ultraviolet, X-ray and radio observations. They narrowed the sample to ten events where they could reliably model both the black hole’s feeding rate and the timing of its radio outflows. The analysis revealed two distinct jet-launching phases. The first occurs early in the event, when the black hole is feeding at extreme rates near the peak of the disruption. The second arrives much later — hundreds to thousands of days after the star is first torn apart — and it is here that the universal rule emerges: the delayed jets ignite when the black hole’s feeding rate falls to roughly two per cent of its Eddington limit.

The Eddington limit is a fundamental benchmark in astrophysics, marking the point at which the outward pressure of radiation exactly balances the inward pull of gravity. Above it, radiation pressure tends to blow away infalling material; below it, matter can settle inward more steadily. Strikingly, the same two-per-cent threshold has long been known to trigger jet formation in stellar-mass black holes in our own Galaxy, objects that can be millions of times lighter than the supermassive monsters at the hearts of distant galaxies. ‘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 implications extend well beyond satisfying theoretical curiosity. The finding neatly explains why some tidal disruption events produce radio jets quickly while others go quiet before flaring up months or years later — the late bloomers were simply waiting for their accretion rates to fall through the critical threshold. It also promises to make astronomers far more efficient users of some of the world’s most expensive and oversubscribed scientific instruments. ‘Radio telescopes are incredibly powerful, but knowing when to look is just as important as knowing where to look,’ Dr Goodwin said. ‘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.’

The timing of the discovery is particularly significant for Western Australia, which will host the low-frequency component of the Square Kilometre Array Observatory (SKA), one of the most ambitious radio astronomy projects ever conceived. The Australian Government has invested 387 million dollars in the SKA, whose total cost exceeds two billion dollars, and every hour of observing time on such a facility is precious. As next-generation surveys discover far more tidal disruption events than current instruments can, astronomers will need reliable ways to decide which events to follow and when. This research hands them a clear physical signal for when a black hole’s jet is most likely to appear. As Forrest Research Foundation Director Professor James Arvanitakis observed, the discovery shows why backing early-career researchers to pursue difficult, open-ended questions matters — a question funded without a predetermined answer has produced a result of international significance, sharpening how major scientific infrastructure is used and demonstrating the strength of Western Australia’s research ecosystem. The paper, ‘A universal critical accretion rate for black hole jet formation’, was published in Nature Astronomy on 17 September 2026.

Subject of Research: Universal critical accretion rate governing jet formation by black holes during tidal disruption events

Article Title: WA scientist helps crack black hole ‘burp’ mystery

Article References: WA scientist helps crack black hole ‘burp’ mystery. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: black holes, jets, tidal disruption events, accretion, Eddington limit, radio astronomy, supermassive black holes, Nature Astronomy, Curtin University, ICRAR, Square Kilometre Array, astrophysics

The question of universality has been difficult to answer because of the sheer disparity of timescales involved. Stellar-mass black holes, which weigh in at a few to a few dozen times the mass of the sun, evolve quickly: their accretion disks brighten and fade over weeks and months, and astronomers have watched them undergo state transitions many times. During these outbursts, the accretion flow switches between a hot, radiatively inefficient mode and a cooler, geometrically thin disk, and it is precisely at these transitions that jets are switched on or off. Decades of monitoring have pinned down the critical accretion rate at which this happens with considerable precision.

Supermassive black holes, by contrast, are far less cooperative. The accretion flows that power active galactic nuclei evolve over thousands of years, which means that no single observer—or even several generations of observers—can watch one system cross the critical threshold where jets are born. As a result, whether the well-established rules of stellar-mass black holes apply to their supermassive cousins remained an open and contested question, one with profound implications for how galaxies grow and how black holes shape their cosmic environments.

Goodwin and Mummery realized that tidal disruption events offered a way around this bottleneck. When a star wanders too close to a supermassive black hole, tidal forces rip it apart, and its debris forms a glowing accretion disk around the hole. Unlike ordinary active galactic nuclei, these newly formed disks evolve dramatically on timescales of just years, blazing bright at super-Eddington accretion rates before fading steadily. That means a single tidal disruption event can carry a black hole through the entire range of accretion rates where jets are expected to appear, all within a human lifetime.

The researchers assembled multiwavelength data for a sample of tidal disruption events, combining radio observations—which trace outflows launched by the black hole—with detailed modeling of the evolving accretion disk using publicly available fitting tools. The disk modeling allowed them to reconstruct the accretion rate of each system at any moment in its evolution, while the radio data, interpreted through synchrotron spectral fitting, revealed when outflows were launched and how fast they were moving. By cross-referencing the two, they could determine the accretion rate at the precise moment each outflow was ejected.

The results were striking. Every tidal disruption event in the sample launched an early outflow while accreting at super-Eddington rates, consistent with the powerful disk winds expected when radiation pressure overwhelms gravity. But many systems also produced a second, physically distinct outflow later in their evolution, and these delayed ejections occurred when the disk accretion rate had fallen to a critical value of roughly two percent of the Eddington luminosity—the same threshold, scaled by mass, at which stellar-mass black holes are known to undergo their hard-to-soft state transitions and launch their characteristic compact jets. In one well-studied event, ASASSN-14li, the accretion rate at the time of outflow launch could be constrained with particular precision, and it matched the universal value.

This convergence is remarkable because the two classes of systems differ by factors of a million or more in black hole mass. The Eddington rate itself scales with mass, so expressing the accretion rate as a fraction of the Eddington value is the natural way to compare systems across cosmic scales. That the critical fraction comes out the same—about two percent—for both stellar-mass black holes and supermassive black holes strongly suggests that the physical mechanism responsible for jet launching does not care about scale. The processes are thought to involve the geometry of the inner accretion flow, where a hot, tenuous, magnetized plasma can collimate magnetic fields into a jet, and the new results indicate that the conditions for this configuration arise at the same fractional accretion rate regardless of the black hole’s mass.

The framework also resolves a puzzle that has dogged tidal disruption observers for years: why some events show prompt radio emission, why others flare in radio years after the optical outburst, and why surveys now routinely detect late-time radio re-brightenings that earlier models struggled to explain. In the new picture, the prompt outflows are super-Eddington winds ejected when the disk first forms, while delayed radio flares mark the launch of a second, jet-like outflow as the fading disk crosses the universal critical threshold. The timing of the delayed flares should then depend on how quickly each disk evolves from its super-Eddington peak down to two percent of Eddington, a prediction the authors tested with a modeled population of tidal disruption disks and found consistent with the observed distribution of outflow launch times.

Beyond tidally disrupted stars, the findings extend naturally to the broader population of accreting black holes. The critical threshold provides a predictive tool: given a black hole’s mass and its current accretion rate, astronomers can now estimate whether jets should be on or off, and when a fading system will cross the line. For active galactic nuclei, whose long-term evolution is normally inaccessible, this offers a way to infer jet activity from snapshot measurements of accretion rate. It also connects to long-standing empirical relations, such as the fundamental plane of black hole activity that links radio and X-ray luminosities across mass scales, which hinted at scale-invariant physics but lacked the direct observational anchor that tidal disruption events now supply.

The implications reach beyond pure astrophysics. Jets launched by supermassive black holes inject enormous amounts of energy into their host galaxies, heating gas, suppressing star formation, and shaping the largest structures in the universe. Understanding exactly when and why these jets switch on is therefore essential for modeling galaxy evolution itself. If a single scale-invariant threshold controls jet formation everywhere, simulations of galaxy feedback can be anchored to a universal rule rather than calibrated separately for each mass regime. And with new time-domain surveys set to discover tidal disruption events by the thousands in the coming years, the framework developed by Goodwin and Mummery promises a growing catalog of natural experiments—each a black hole caught mid-transformation, its jet poised to switch on at the same universal moment.

Subject of Research: The universal critical accretion rate governing jet formation in black holes across mass scales, probed through tidal disruption events

Article Title: A universal critical accretion rate for black hole jet formation

Article References: A universal critical accretion rate for black hole jet formation. (n.d.). https://doi.org/10.1038/s41550-026-02951-1

Image Credits: AI Generated

DOI: 10.1038/s41550-026-02951-1

Keywords: black holes, jets, tidal disruption events, accretion, supermassive black holes, Eddington limit, radio astronomy, active galactic nuclei, outflows, state transitions, accretion disks, Nature Astronomy