A universal critical accretion rate for black hole jet formation

Abstract

It has long been suspected that black hole accretion–outflow coupling is invariant from 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 an 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 Lcrit ≈ 0.02 LEdd, 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. 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 agreement in this critical accretion rate across such vastly different mass scales strongly indicates that a single, scale-invariant physical process governs jet launching in all black holes. This work additionally provides a framework that allows for strong future predictions of which black holes will launch jets, and when.