A Black Hole Jet Just Became a 27-Year Movie
A neural reconstruction turned 116 radio snapshots into a continuous movie of plasma racing from a distant black hole. The bright knots may not be the shocks astronomers assumed.
The Discovery
Astronomers have reconstructed a continuous, polarized movie of a relativistic jet using 116 radio observations collected between 1995 and 2022. The target, blazar 3C 345, fires plasma almost directly towards Earth from a supermassive black hole.
The peer-reviewed Nature study introduces an imaging method called kine. Instead of treating every observation as a separate still, the neural representation learns the shared structure across time and lets researchers sample the jet between measured epochs.
What Makes It Strange
Traditional very long baseline interferometry tracks broad bright components from one image to the next. Kine reconstructed the local flow field itself, producing about four times the nominal angular resolution and a dynamic range roughly 140 times greater than conventional frame-by-frame imaging.
- The observations came from the Very Long Baseline Array's MOJAVE programme.
- The reconstructed jet extends about 13 milliarcseconds from its core.
- Apparent flow speeds peak near 12 times the speed of light because of relativistic motion aimed close to our line of sight.
- Bright knots and surrounding plasma moved at similar inferred speeds.
The telescope took snapshots. The mathematics found the motion between them.
The Implications
The comparable speeds challenge a common picture in which every bright component is a strong shock travelling through a different bulk flow. Polarization maps also lacked the local ordering expected from strong compression. The authors instead favour regions of enhanced emission within a turbulent, magnetized stream for this source.
Nothing in the result breaks relativity. Apparent superluminal motion is a projection effect produced when plasma moves near light speed at a small angle towards the observer. The reconstruction also relies on smooth spatiotemporal correlations, so its inferred frames are model outputs constrained by data, not direct exposures taken at every instant.
What Happens Next
The team originally developed kine for rapidly changing sources such as Sagittarius A* at Event Horizon Telescope scales. Applying it to other jets will test whether 3C 345 is unusual or whether bright features have routinely been mistaken for travelling shocks.
A black hole's jet no longer has to be frozen into a stack of still images. It can be watched as weather.