A wide and collimated radio jet in 3C84 on the scale of a few hundred gravitational radii

Understanding the formation of relativistic jets in active galactic nuclei remains an elusive problem ¹ .This is partly because observational tests of jet formation models suffer from the limited angular resolution of ground-based very-long-baseline interferometry that has thus far been able to probe the structure of the jet acceleration and collimation region in only two sources ^2,3 . Here, we report observations of 3C84 (NGC 1275)-the central galaxy of the Perseus cluster-made with an interferometric array including the orbiting radio telescope of the RadioAstron ⁴ mission. The data transversely resolve the edge-brightened jet in 3C84 only 30 μas from the core, which is ten times closer to the central engine than was possible in previous ground-based observations ⁵ and allows us to measure the jet collimation profile from ~10² to ~10⁴ gravitational radii (r _g) from the black hole. The previously found ⁵, almost cylindrical jet profile on scales larger than a few thousand r _g is seen to continue at least down to a few hundred r _g from the black hole, and we find a broad jet with a transverse radius of â‰250 r _g at only 350 r _g from the core. This implies that either the bright outer jet layer goes through a very rapid lateral expansion on scales â‰10² r _g or it is launched from the accretion disk.