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Currently Playing: Twisting Magnetic Fields Near OJ 287 | Event Horizon Telescope

This animation illustrates the interaction between propagating shock waves and a Kelvin-Helmholtz helical wave pattern in a jet threaded by a helical magnetic field, based on Event Horizon Telescope observations of the supermassive black hole candidate OJ 287 at 1.3 mm wavelength on April 5 and 10, 2017. The left panel shows the jet structure at scales of 10-100 gravitational radii (approximately 0.2 light-days) from the black hole, where the helical magnetic field (orange threads) and Kelvin-Helmholtz wave pattern (red helix, wavelength ~100 microarcseconds or 1.5 light-years) coexist. Two bright shock components, C1 (cyan) and C2 (pink), propagate downstream at different speeds. As these shocks move through the helical structure, they interact with different phases of the instability, illuminating localized regions and producing opposite-direction electric vector position angle (EVPA) rotations: the faster component C1 rotates counterclockwise at ~3.7° per day, while the slower component C2 rotates clockwise at ~2.5° per day. Component C3 (green) marks a stationary recollimation shock with radial polarization. The right panel displays the EVPA evolution over the five-day observation period. These spatially resolved opposite-direction rotations provide the first direct observational evidence that a helical magnetic field threads the jet’s collimation and acceleration zone, ruling out models based solely on the superposition of unresolved components. Credit: EHT Collaboration | Animation: E. Traianou