The Active Galactic Nucleus of 3C 120

Illustration of a shock wave (bright "blob" in the upper jet) following a spiral path (in yellow) as it moves away from the black hole BL Lacertae. The blob plows through a section of the jet where the magnetic field (light blue curved lines) is wound up in a coil. This caused a brightening seen in visible, X-ray, and Gamma-ray light; later, the shock passed through the stationary X-shaped compression in the jet and brightened a second time.