Black holes from stellar to supermassive size may follow one jet-launching rule

An early-career Western Australian astrophysicist has helped uncover a universal rule behind one of the most powerful behaviors in the universe: when black holes launch jets. The discovery, published in the journal Nature Astronomy, shows black holes appear to fire off powerful jets at the same critical point in their feeding cycle—whether they are about 10 times the mass of the sun or millions of times heavier. The work was led by Dr. Adelle Goodwin, an astrophysicist at Curtin University's International Center of Radio Astronomy Research (ICRAR) and a Forrest Research Foundation fellow, with co-author Dr. Andrew Mummery from the Institute for Advanced Study in Princeton. The finding is the result of years spent piecing together observations from telescopes around the world, including Australia, the United States, India, South Africa and space—tracking rare events where stars are torn apart by supermassive black holes and watching what happens next and why.

The puzzle of delayed jets Goodwin said the breakthrough came from trying to answer the following question: Why do some black holes produce radio jets soon after tearing apart a star, while others appear to switch on months or years later? "We were looking at these events and asking why the timing was so different," 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 realized this was not just a quirk of one type of black hole, but it looked like a rule that applied across the universe."

Black holes as messy eaters Black holes are often described as cosmic vacuum cleaners, but Goodwin said they were more like messy eaters. "When a black hole tears apart a star, it does not swallow everything neatly," Goodwin said. "Some of the material is consumed, and some is launched back into space in powerful jets and outflows. "You can think of it as a black hole burp, except these burps can blast material across enormous distances and influence the galaxies around them." A compressed cosmic experiment For decades, astronomers have suspected black holes might follow the same basic physics regardless of their size—but proving it has been difficult because supermassive black holes usually evolve over thousands of years. Goodwin found a way around that problem by studying tidal disruption events, which occur when a star strays too close to a supermassive black hole and is ripped apart. These rare events compress a supermassive black hole feeding episode into years rather than millennia, giving astronomers a chance to watch the process unfold. The researchers analyzed 20 tidal disruption events using optical, ultraviolet, X-ray and radio observations, narrowing the sample to 10 events where they could reliably model both the black hole's feeding rate and the timing of its radio outflows. They found two distinct jet-launching phases. The first happens early, when the black hole is feeding at extreme rates. The second comes much later, hundreds to thousands of days after the star is first torn apart, when the black hole's feeding rate drops to about 2% of its Eddington limit—the point at which outward radiation pressure balances gravity. The same 2% threshold is already known to trigger jet formation in much smaller black holes in our galaxy. "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," Goodwin said. "That tells us something fundamental about black holes: The physics does not seem to care how big they are."

The discovery helps explain why some tidal disruption events produce radio jets quickly, while others appear to go quiet before suddenly lighting up much later. It could also help astronomers make better use of some of the world's most expensive and in-demand scientific instruments. "Radio telescopes are incredibly power

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