Black hole jet formation appears to obey a single critical threshold regardless of whether the black hole in question weighs ten times the mass of our Sun or millions of times more, according to a study published in Nature Astronomy on 17 September 2026. The research, led by Andrew Mummery at the Institute for Advanced Study and Adelle Goodwin at Curtin University’s International Centre of Radio Astronomy Research in Western Australia, draws on observations across optical light, ultraviolet light, X-rays, and radio waves gathered from telescopes in America, Australia, India, South Africa, and space.
The claim at the centre of the paper is precise: jets from supermassive black holes form at the same critical feeding rate, as a fraction of the Eddington limit, as jets from the much smaller stellar-mass black holes already studied within the Milky Way. If the methodology holds up to scrutiny, it would mean that the physics governing jet production does not fundamentally change across an enormous range of masses. That is the kind of claim that needs a clear evidential base, so it is worth looking at how the researchers built their case.
Tidal Disruption Events as a Research Tool
The main obstacle to studying supermassive black holes in real time is one of timescales. Changes in the environment around them can normally unfold over thousands or even millions of years, making direct observation of any single process nearly impossible. Tidal disruption events offer a partial solution. When a star passes close enough to a supermassive black hole that gravitational forces tear it apart, the resulting feeding episode can evolve over just a few years. That compression of timescale gives researchers a window onto processes that would otherwise be inaccessible.
The team examined twenty such events, eventually narrowing the sample to ten for which they could reliably determine both the black hole’s feeding rate and the timing of its radio outflows. The quality cut matters: working with unreliable feeding-rate data would undermine the central comparison the study is trying to make.
The Two Percent Threshold Behind Black Hole Jet Formation
The analysis identified two distinct periods when jets can form. The first occurs early, while the black hole is consuming material at a very high rate. The second appears much later, hundreds to thousands of days after the star was initially torn apart. At that later stage, the black hole’s feeding rate falls to about two percent of its Eddington limit, the point at which outward radiation pressure balances the inward pull of gravity.
That two percent figure is already established as a jet-triggering threshold for stellar-mass black holes within our galaxy. Finding the same fraction associated with jet formation in supermassive black holes is the paper’s core result. As Universe Magazine noted in its coverage, the absolute luminosity involved differs enormously between the two scales: for a black hole with a mass of one million Suns, two percent of the Eddington limit corresponds to a luminosity of about 650 million Suns, while for an object with a mass of ten Suns, the same fraction produces only about six thousand. The threshold is the same in relative terms; the physical consequences are wildly different in absolute ones.
‘We really wanted to figure out this massive puzzle,’ Mummery said. ‘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?’ The study, published under the title ‘A universal critical accretion rate for black hole jet formation,’ is the researchers’ answer to that question.
Goodwin offered a reminder that the feeding process is not a clean one. ‘When a black hole tears apart a star, it does not swallow everything neatly,’ she stated. Some material falls inward; much of it is expelled outward through powerful outflows that can carry matter across vast distances and affect the evolution of the surrounding galaxy.
What the Finding Could Mean for Future Observations
Beyond the physics, the study has a practical implication. If researchers can use the two-percent threshold to predict when a supermassive black hole is likely to produce a delayed jet, they can schedule telescope time more efficiently and reduce observations made when little activity is expected. The authors suggest this predictive value could be particularly useful for the Square Kilometre Array radio telescope project, which is expected to begin collecting scientific data in 2028.
The idea behind the study, according to the paper, emerged during an astrophysics conference in Madrid, when Mummery and Goodwin realised during a conversation that the jet-triggering rule known for smaller black holes might extend to supermassive ones. EurekAlert! reported the paper’s publication date as 17 September 2026. Whether the ten-event sample the team relied on is large enough to establish universality is a question the authors acknowledge implicitly by calling for further observations, and the Square Kilometre Array, if it meets its 2028 start date, may be what puts the rule to a proper test.
