Matter outflows in the form of jets are observed in astronomical systems at fast, medium and slow speeds. The fastest jets are highly relativistic, and travel very close to the speed of light. The origin, as well as many properties of the jets, is uncertain. Jet velocities seem to have a bi-modal distribution—some very fast and others slow, with a gap in velocities in between, which has long challenged experts. Bar-Ilan University researchers re-examined the data and have now seemingly solved the puzzle.
