Scientists have uncovered a universal rule governing when black holes release powerful jets, or “burps,” revealing that these cosmic eruptions occur when accretion rates drop to 2% of the Eddington limit, regardless of the black hole’s size. The findings, published in Nature Astronomy, could reshape how astronomers observe these phenomena.
For decades, astrophysicists puzzled over why some supermassive black holes emit jets of material years after devouring a star, while others do so immediately. A breakthrough led by Dr. Adelle Goodwin of Curtin University and Dr. Andrew Mummery of the Institute for Advanced Study has now revealed a universal pattern: black holes launch jets when their feeding rate falls to 2% of the maximum sustainable level, a threshold observed in both supermassive and stellar-mass black holes.
The Puzzle of Cosmic Burps
Black holes, often depicted as relentless cosmic vacuum cleaners, are actually very messy eaters, according to Goodwin. When a star ventures too close, it is stretched into a spaghetti-like shape by tidal forces—a process called spaghettification. Only about half of the star’s material is ultimately swallowed by the black hole, while the rest is expelled in jets and outflows. These eruptions, likened to black hole burps, can influence galaxy evolution by heating surrounding gas or triggering star formation.
The timing of these jets had long baffled scientists. Sometimes it would happen a year after the black hole destroyed the star, sometimes it would happen three or five years after, Goodwin said. The new research, which analyzed 20 tidal disruption events using radio telescopes, found that jets consistently emerged when the black hole’s accretion rate fell to 2% of the Eddington limit—a critical threshold also seen in smaller black holes.
Very messy eaters’: scientists solve the mystery of when
Unraveling the Mechanism
The study, published in Nature Astronomy, relied on radio observations to track jets as they expanded outward. Radio is the only frequency where we can watch the jets and outflows as they’re moving outwards,
Goodwin explained. By combining data across optical, ultraviolet, X-ray, and radio wavelengths, the team identified two distinct phases of jet formation: an early burst during high-accretion periods and a delayed eruption when the feeding rate declined to 2%.
The discovery originated during a casual conversation at an astrophysics conference in Madrid. Mummery and Goodwin hypothesized that the same physical principles governing small black holes might apply to supermassive ones. After cross-checking data, they found a perfect alignment between the behavior of stellar-mass and supermassive black holes. We hope that our work will pave the way for even more profound discoveries about our universe,
Mummery said.
Implications for Future Observations
The findings have immediate practical benefits. By predicting when jets will emerge, astronomers can optimize telescope time, particularly for high-demand facilities like the Square Kilometre Array (SKA). We can really start to understand not just when the jets are launched, but also how strong they are and if that is then dependent on the black hole properties,
Goodwin said.
Scientists Find a Universal Rule for Black Hole Jets
Dr. Sara Webb, an astrophysicist at Swinburne University uninvolved in the research, called the study a major step forward. She noted that the work ties back to what we’ve seen previously on the much smaller scale stellar-mass black holes, offering a unified framework for understanding these extreme cosmic events. The research also underscores the importance of multi-wavelength observations in unraveling the mysteries of black hole behavior.
The study, which analyzed 20 tidal disruption events, used the full range of observational wavelengths: optical, ultraviolet, X-ray, and radio. By combining observations across wavelengths, they determined that the onset of black hole jets follows two distinct temporal patterns. The first phase is early, in which the jet appears as soon as the black hole begins to accrete matter at an extremely high rate, while the other phase is delayed. In this case, the jet does not form until hundreds or even thousands of days have passed, by which time the black hole’s accretion rate has dropped to about 2 percent of the Eddington limit.
The research showed that black holes appeared to release jets at the same point in their feeding cycle regardless of size, Goodwin said. She said the finding would enable scientists to precisely predict when such jets would be released, narrowing observation windows and freeing up precious telescope time. This basic physical law is universal and can be applied no matter the size of the black hole,
Mummery stated.
The breakthrough happened at a bar in Madrid during an astrophysics conference, where Mummery and Goodwin immediately thought the rules governing jet formation in small black holes might also apply to these distant supermassive black holes. After cross-checking data, they found that the activity patterns of the two types of black holes aligned perfectly. They then spent several months carefully analyzing the collected data and ultimately confirmed the conjecture.
As the SKA and other next-generation telescopes come online, astronomers are poised to test these findings further. For now, the study provides a critical roadmap for studying one of the universe’s most enigmatic phenomena—proving that even the most massive objects in the cosmos follow a universal rule.