Morphological Transition of the Compact Radio Lobe in 3C 84 via the Strong Jet–Cloud Collision

We report multiepoch very long baseline interferometric observations of the compact radio lobe in the radio galaxy 3C 84 (NGC 1275) during 2016–2020. The image sequence of 3C 84 reveals that the hotspot in the radio lobe showed the 1 year long frustration in 2017 within a compact region of about 0.07 pc, suggesting a strong collision between the jet and a compact dense cloud with an estimated average density of about (4–6) × 105 cm−3. Although the hotspot and the radio lobe began to move south again after its breakout, the radio lobe showed a morphological transition from an FR II- to FR I-class radio lobe and its radio flux became fainter. This is the first detection of the dynamical feedback from the cloud to the jet where the cloud located on the jet axis significantly interferes with the jet propagation and evolution at the central 1 pc region in the active galactic nucleus.