Black Holes Fire Jets at Same 2% Eddington Limit

A team led by a researcher at the Institute for Advanced Study (IAS) in Princeton has found a rule that appears to hold for black holes of every size: their jets switch on at the exact moment their feeding rate drops to about 2 percent of the Eddington limit, the point where radiation pressure balances gravity. The paper appeared on September 17, 2026, in Nature Astronomy under the title “A universal critical accretion rate for black hole jet formation,” with the identifier DOI 10.1038/s41550-026-02951-1. Its authors are Andrew Mummery of the IAS and Adelle Goodwin of the International Centre for Radio Astronomy Research (ICRAR) at Curtin University in Western Australia.

The team reached its conclusion by studying tidal disruption events, the episodes in which a black hole’s gravity tears apart a star that strays too close. Those events gave them a shortcut: while a supermassive black hole normally feeds in cycles lasting thousands to millions of years, a tidal disruption compresses that entire process into just a few years, letting the team watch it unfold from start to finish.

What the Team Analyzed

Mummery and Goodwin reviewed data from twenty tidal disruption events, gathered in optical, ultraviolet, X-ray and radio wavelengths. Of those twenty, they picked out the ten with the highest quality data, the ones where they could reliably model both the black hole’s feeding rate and the timing of its radio echo, in other words its jet. The breakthrough, as the research describes it, did not come from combing through telescope data but from a conversation at an astrophysics conference in Madrid, where the team noticed that the same rule governing small black holes in our own galaxy seemed to apply to supermassive ones too.

The analysis showed the jet appears in two separate phases. The first comes early, while the black hole is swallowing material at its fastest, around the peak of feeding. The second phase arrives much later, once the feeding rate has fallen to roughly that 2 percent Eddington threshold. Neither the Institute for Advanced Study’s own announcement nor the Science Times report on it gives an exact number of days between the star’s disruption and that later, second phase; both sources describe only a range of “hundreds to thousands of days” afterward, without a precise figure.

That same 2 percent Eddington threshold is already known as the trigger for jets in much smaller, stellar-mass black holes in our galaxy, the kind weighing around ten solar masses. Finding that the same rule holds for black holes millions of times heavier is, according to the researchers, what makes the physics of the process universal.

Why It Happens

“Why do some supermassive black holes fire off radio jets right after shredding a star, while others just sit quietly, only switching a jet on months or years later,” is how Andrew Mummery, a researcher at the Institute for Advanced Study, framed the question the team set out to answer, in the IAS statement carried on EurekAlert.

Black holes, says Adelle Goodwin, are often described as cosmic vacuum cleaners, but that description misses the mark.

“When a black hole shreds a star, it doesn’t swallow it all neatly.”

Adelle Goodwin, a Forrest Research Foundation researcher at Curtin University, adds in the same statement that a large share of that material, rather than being swallowed, gets violently flung back out into space in powerful jets, which the researchers themselves describe in the paper as cosmic “burps.”

Mummery closes the statement with this thought:

“We hope our work paves the way toward still deeper discoveries about our universe.”

The Practical Side of the Discovery

Beyond settling a long-standing puzzle over why some black holes fire their jets late, the finding has an immediate practical use. If astronomers know when a black hole is most likely to switch on a delayed jet, they can plan their telescope time around that window instead of scattering observations blindly. That should cut down on missed observations and raise the odds of catching the short window when a jet actually appears, a benefit that extends to future instruments such as the Square Kilometre Array radio telescope, whose science data collection is slated to begin in 2028.

What This Study Doesn’t Prove

The paper rests on ten closely modeled events out of twenty analyzed in total, a sample large enough to show a consistent pattern in tidal disruption events but not enough to prove that the identical mechanism holds without exception for every black hole and every type of feeding in the universe. The study also does not pin down the exact number of days that pass before that second jet phase; that figure remains open until more precise numbers from the paper itself are published. Most researchers in the field had assumed until now that jet physics depends on a black hole’s size, so the finding that the same threshold applies universally still needs to be tested against additional samples beyond tidal disruption events.