When a supermassive black hole tears apart a star (a tidal disruption event), it can launch a jet right away while it is feeding very fast, or stay quiet for hundreds or even thousands of days before a jet appears. A study published in Nature Astronomy in October 2026 found that these delayed jets switch on when the black hole’s feeding rate falls to about 2% of its Eddington limit, the point where outward radiation pressure balances gravity.
The same 2% threshold was already known to trigger jets in much smaller black holes in the Milky Way, about 10 times the mass of the Sun, which suggests one rule applies regardless of size. Researchers Adelle Goodwin (Curtin University, ICRAR) and Andrew Mummery (Institute for Advanced Study) reached the result by comparing 10 well-observed tidal disruption events, and say it could help radio astronomers predict when to watch for new jets.
Image: Artist’s concept of a star being torn apart by a supermassive black hole, with a jet of material launched outward. NRAO/AUI/NSF/NASA, public domain, via Wikimedia Commons.
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