Black holes are like cosmic drains. As they pull in matter, they sometimes spew out jets. For giants at the centers of galaxies, this process drags on for millions of years, hiding any regime changes. But when a hapless star gets too close and gets turned into 'spaghetti', everything speeds up. Observations showed: the key transition occurs at the same level of brightness — when it drops to 2% of the maximum, beyond which light itself would have blown away the infalling gas. This threshold works for both black holes weighing a few Suns and monsters billions of Suns. It's as if a kitchen sink and a giant ocean whirlpool changed their splash pattern at the same water pressure. This explains the puzzling delays in jet appearances and proves that the physics of cosmic drainage is universal.
as written by the authors arXiv:2602.14838
It has long been suspected that black hole accretion-outflow coupling is invariant from the stellar to supermassive scales. Stellar mass black hole accretion flows are known to launch jets and outflows as they transition through critical accretion rate thresholds, with values well constrained observationally owing to their short evolutionary timescales. In contrast, accretion flows in typical supermassive black hole (SMBH) systems (those in active galactic nuclei) evolve over thousands of years, making the critical transitions at which jets are launched impossible to constrain in individual systems. Tidal disruption events (TDEs) provide the unique opportunity to witness the birth and evolution of an accretion flow onto a SMBH which evolves on timescales of years. Here we show that TDEs launch outflows during a super-Eddington accretion phase and a second, physically distinct outflow, at a critical accretion rate of $$L_{\rm crit} \approx0.02$$ $$L_{\rm Edd}$$, the same as the critical accretion rate for state transitions observed in accreting stellar mass black holes. This work naturally explains the mechanism, observed properties, and detection rate for prompt and delayed outflows observed in TDEs, which until now have been open problems. More broadly, we demonstrate that SMBHs exhibit the same accretion-outflow coupling as stellar mass black holes and that the critical low accretion rate threshold for jet formation in black holes is scale invariant.
The brightness limit beyond which light blows away matter, for a 10-million-solar-mass black hole, is comparable to the radiance of hundreds of billions of suns. Just 2% of that value is still a dazzling blaze, and exactly at that level the hole switches its ejection mode.
In 'Interstellar,' the black hole Gargantua tears apart a star — similar real-life catastrophes led to the discovery of a unified law for black holes.