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Black Holes Turn On Jets at Same Feeding Threshold

New Nature Astronomy research shows delayed jets ignite when accretion falls to about 2% of the Eddington limit, giving astronomers a clear timing cue for radio follow-up.

Overview

  • The study, published Thursday, 17 September 2026, reports a universal rule where black holes from stellar mass to supermassive launch delayed jets when their feeding rate drops to roughly two percent of the Eddington limit.
  • Researchers analysed 20 tidal disruption events and focused on 10 high-quality cases where optical, ultraviolet, X-ray and radio data let them model the black hole feeding rate and the timing of radio outflows.
  • The team identifies two jet-launching phases: an early, prompt phase at very high accretion and a delayed phase that appears hundreds to thousands of days later when accretion falls to the 2% threshold.
  • The Eddington limit is the balance where outward radiation pressure counters gravity, so the 2% mark is a specific accretion rate rather than a measure of power and it matches a threshold already seen in small black holes in our Galaxy.
  • The result gives a practical scheduling tool for high-demand radio facilities such as the SKA, and the international collaboration led by early-career researchers highlights how coordinated multi-wavelength campaigns can boost the yield of rare, time-sensitive discoveries.