"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."

For practitioners, the takeaway is simple: delayed jets are not random; they track a measurable feeding threshold.

How did the researchers reach the 2% figure?

The team initially examined 20 tidal disruption events, combining observations from telescopes in Australia, the United States, India, South Africa, and space, across visible light, ultraviolet, X-ray, and radio wavelengths. They then narrowed the sample to 10 events with data solid enough to estimate both the matter-consumption rate and the timing of radio outflows.

The comparison revealed two distinct jet-producing stages:

• An early stage, while the black hole consumes matter at an exceptionally high rate.
• A delayed stage, hundreds or even thousands of days after the star's destruction, when the feeding rate falls to about 2% of the Eddington limit.

The Eddington limit is the point at which outward radiation pressure balances inward gravity; astronomers use it as a benchmark for how intensely a black hole is feeding. The same 2% threshold already appears in jet formation by small black holes inside the Milky Way, which is what makes the supermassive match striking.

Notably, the key insight did not arrive at a telescope. Goodwin and Mummery recognized the pattern during a conversation at a bar in Madrid, while attending a scientific conference.

What changes for radio astronomy?

Observing time on major radio facilities is limited and competitive. If astronomers can estimate when a feeding black hole will approach the 2% threshold, they can schedule observations around likely jet launches.

"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 stakes are concrete for Western Australia, which will host the low-frequency component of the Square Kilometre Array Observatory (SKA). The Australian Government has invested $387 million in the SKA; the project's total cost exceeds $2 billion. Efficient targeting could squeeze more discovery out of that infrastructure. As new surveys identify growing numbers of tidal disruption events, the feeding-rate rule gives researchers a filter for deciding which ones deserve follow-up.

How solid is the result?

The finding rests on 10 well-characterized events out of an initial pool of 20 — a small sample drawn from rare phenomena. The researchers describe a consistent pattern, not a tested forecasting tool, and the paper's claim is that the threshold "appears" universal across masses. Expect the rule to face stricter tests as surveys deliver more events.

The broader significance, though, is already clear: the same basic physics seems to govern black holes across vastly different scales.

Professor James Arvanitakis, Director of the Forrest Research Foundation, which funded Goodwin's fellowship, framed the result as an argument for open-ended research. "The Forrest Research Foundation did not fund a predetermined answer, we backed an exceptional researcher with a difficult question," he said. "That question has led to a discovery of international significance."

One rule, two very different black holes, and a better clock for the universe's loudest burps.