A cosmic double helix in the archetypical quasar 3C273

Finding direct evidence for plasma instability in extragalactic jets is crucial for understanding the nature of relativistic outßows from active galactic nuclei. Our radio interferometric observations of the quasar 3C273 made with the orbiting radio telescope, HALCA, and an array of ground telescopes have yielded an image in which the emission across the jet is resolved, revealing two threadlike patterns that form a double helix inside the jet. This double helical structure is consistent with a Kelvin-Helmholtz instability, and at least Þve different instability modes can be identiÞed and modeled by a light jet with a Lorentz factor of 2 and Mach number of 3.5. The model reproduces in detail the internal structure of the jet on scales of up to 30 milliÐarc seconds (;300 parsecs) and is consistent with the general morphology of the jet on scales of up to 1 kiloparsec. One of the most intriguing features observed in active galactic nuclei (AGN) is highly collimated, relativistic plasma outflows ( jets