Black Hole Jets Follow the Same Rule Whether Stellar or Supermassive

# What the study looked at

# Accretion, the Eddington limit, and jets Accretion onto a black hole produces an accretion disk of hot plasma. As the accretion rate rises, the disk emits more heat and light, and radiation pressure can push gas away. The maximum steady rate where radiation pressure balances gravity is the Eddington limit. If a black hole accretes too rapidly, thermal pressure can clear away infalling material and shut down steady accretion.

Stellar-mass black holes do not need to approach the Eddington limit to launch jets. Observations show jets appear when accretion reaches about 2% of the Eddington limit, which explains why many stellar-mass black holes are observed with jets.

# What tidal disruption events reveal TDEs allow supermassive black holes to consume matter at very high rates, sometimes briefly above the Eddington limit. The study examined twenty TDEs across radio, optical, ultraviolet, and X-ray bands. For roughly half of those events the team could estimate both accretion rates and whether jets formed.

# The core result: scale invariance For long-term jet formation the same accretion threshold applies across mass scales. When a black hole consumes material at or above ~2% of the Eddington limit, whether it's a few solar masses or millions to billions of solar masses, an accretion disk can produce jets. That makes the jet-formation process scale invariant: similar accretion physics govern both stellar and supermassive systems.

# Why this matters for observation and modeling Because the threshold is similar, well-observed stellar-mass systems—where accretion and state changes happen on much shorter timescales—provide accessible laboratories to study disk-jet coupling relevant to supermassive black holes. TDEs supply opportunities to watch a supermassive black hole pass through a super-Eddington phase and later settle into the same low-percent-Eddington regime associated with persistent jets.

# Remaining questions and context Not every TDE or accreting supermassive black hole produces bright X-ray emission or jets, and the reasons for those differences remain uncertain. The study's sample showed that initial super-Eddington bursts and later secondary jets occur for bright TDEs, but there are TDEs without clear X-ray bursts and some supermassive black holes form jets without bright TDE signatures. Those instances indicate additional factors beyond simple accretion rate may influence whether jets are launched or observed.

# Practical takeaway for researchers When modeling jet formation or interpreting observations, use the ≈2% Eddington accretion threshold as a predictive baseline for the onset of sustained jets across black hole masses. Compare rapid, accessible state changes in stellar-mass binaries to the slower evolution seen after TDEs to test disk-jet coupling mechanisms.