Black Holes Big and Small Follow the Same Universal Rule for Launching Jets

Black holes have a reputation as the universe’s most voracious eaters, but the reality is messier and far more dramatic. When one of these gravitational monsters tears a star apart, it does not swallow everything cleanly. Instead, a substantial fraction of the stellar debris is hurled back into space in violent outflows that astronomers colloquially describe as cosmic burps. Now, an international collaboration co-led by a scholar at the Institute for Advanced Study has shown that these eruptions obey a single, universal rule, one that holds true whether the black hole involved is a stellar-mass object roughly ten times the mass of our sun or a supermassive giant weighing millions of solar masses. The discovery, published in Nature Astronomy, reveals that black holes of radically different sizes fire their powerful jets at precisely the same critical point in their feeding cycles.

The research was led by Andrew Mummery, the Martin A. and Helen Chooljian Member in the Institute for Advanced Study’s School of Natural Sciences, working alongside Adelle Goodwin, a Forrest Research Foundation Fellow at Curtin University’s International Centre of Radio Astronomy Research in Western Australia. Their study, titled A universal critical accretion rate for black hole jet formation, represents the culmination of years of painstaking analysis. The team assembled multi-wavelength observations from telescopes positioned across the globe, including facilities in America, Australia, India, and South Africa, as well as instruments in space. By tracking tidal disruption events, the spectacular occasions when stars are shredded by the immense gravitational forces of supermassive black holes, the researchers were able to watch exactly what happens in the aftermath of these cosmic catastrophes.

The central puzzle that motivated the work was a long-standing inconsistency in the behavior of supermassive black holes. Some blast out bright radio jets almost immediately after shredding a star, while others appear completely dormant, only to suddenly switch on their jets months or even years later. We really wanted to figure out this massive puzzle, Mummery explained. 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 answer, it turns out, lies in the physics of accretion, the process by which black holes consume the matter swirling around them.

When a black hole tears apart a star, the resulting debris does not simply vanish down the drain. While a portion of the material is consumed, much of it is violently launched back into space in powerful outflows, as Goodwin noted. These immense cosmic burps can blast material across staggering distances, and their influence extends far beyond the immediate vicinity of the black hole itself. The energy injected into the surrounding gas can heat and stir the interstellar medium of the host galaxy, potentially regulating star formation and fundamentally shaping the galaxy’s long-term evolution. Understanding when and why these jets switch on is therefore not just a matter of curiosity about black holes, but a key ingredient in the broader story of how galaxies grow and change over cosmic time.

For decades, astrophysicists have suspected that black holes follow the same basic laws of physics regardless of their immense variations in size. The equations governing accretion disks and jet formation should, in principle, scale smoothly from the smallest stellar-mass systems to the largest supermassive ones. Proving this, however, has historically been extraordinarily difficult. The problem is one of timescales. Supermassive black holes typically evolve over thousands or millions of years, far longer than any observational campaign can realistically monitor. Stellar-mass black holes, by contrast, cycle through their feeding states in days or weeks, which is why most of what astronomers know about accretion physics comes from these smaller systems within our own galaxy.

Tidal disruption events offered a way around this bottleneck. Because a star wandering too close to a supermassive black hole is destroyed in a single catastrophic encounter, the entire feeding episode that follows is compressed into a timeframe of mere years. This grants researchers a unique window into the dynamic process as it unfolds, effectively speeding up the slow-motion evolution of a supermassive accretion flow into something observable within a human career. The pivotal moment of realization for the team, fittingly, did not come while trawling through telescope data but in a bar in Madrid during an astrophysics conference. It was there that Mummery and Goodwin recognized that the same underlying rule dictating jet launches in small black holes appeared to apply universally to their supermassive cousins.

Turning that flash of insight into a rigorous result required meticulous observational work. The team analyzed twenty tidal disruption events using optical, ultraviolet, X-ray, and radio observations, ultimately narrowing their sample to ten high-quality events in which they could reliably model both the black hole’s feeding rate and the timing of its radio outflows. The analysis revealed two distinct jet-launching phases. The first occurs early in the event, when the black hole is feeding at extreme rates and the debris stream is at its most turbulent. The second phase arrives much later, hundreds to thousands of days after the star is first torn apart, and it follows a remarkably precise prescription.

That prescription is the heart of the discovery. The delayed jets switch on when the black hole’s feeding rate drops to approximately two percent of its Eddington limit, the critical luminosity at which the outward pressure of radiation exactly balances the inward pull of gravity. Below this threshold, the structure of the accretion flow changes in ways that favor the launching of collimated, radio-bright jets. What makes the result so striking is that the same two percent threshold is already known to trigger jet formation in much smaller black holes in our own galaxy. The fundamental piece of physics governing when a black hole launches a jet, in other words, scales universally across eight or more orders of magnitude in mass, from compact stellar remnants to the supermassive engines at the hearts of distant galaxies.

Beyond resolving a decades-old mystery, the findings carry immediate practical benefits for the astronomy community. Because researchers can now predict precisely when a black hole is most likely to launch a delayed jet, they can anticipate these events rather than simply waiting for them to happen. This predictive power allows observatories to optimize the use of instruments that are in extraordinarily high demand worldwide. Targeted observing campaigns can be scheduled with far greater efficiency, reducing wasted telescope time and improving the odds of capturing these fleeting radio flares as they unfold. The implications are particularly significant for next-generation facilities such as the Square Kilometre Array radio telescope project, which is poised to begin collecting scientific data in 2028 and will require careful scheduling to maximize its scientific return.

The work stands as a vivid demonstration of how combining theoretical insight with coordinated, multi-wavelength observations can uncover universal laws in the most extreme environments the universe has to offer. By linking the feeding behavior of black holes across the entire mass spectrum, Mummery and Goodwin have given astronomers both a conceptual framework and a practical forecasting tool. We hope that our work will pave the way for even more profound discoveries about our universe, Mummery said. As new tidal disruption events are detected at an accelerating pace by current and upcoming surveys, the universal two percent rule will face ever-stricter tests, and each new jet that switches on schedule will add another piece of evidence that, when it comes to burping, black holes of every size play by exactly the same rules.

Subject of Research: Universal critical accretion rate governing black hole jet formation in tidal disruption events

Article Title: IAS scholar reveals universal rule of black hole "burps"

Article References: IAS scholar reveals universal rule of black hole "burps". (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: black holes, tidal disruption events, astrophysics, radio jets, accretion, Eddington limit, supermassive black holes, stellar-mass black holes, Nature Astronomy, Institute for Advanced Study, Square Kilometre Array, jet formation