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

Abstract

Understanding the formation of relativistic jets in active galactic nuclei remains an elusive problem1.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 sources2,3. 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 RadioAstron4mission. 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 observations5and allows us to measure the jet collimation profile from ~102to ~104gravitational radii (rg) from the black hole. The previously found5, almost cylindrical jet profile on scales larger than a few thousand rgis seen to continue at least down to a few hundred rgfrom the black hole, and we find a broad jet with a transverse radius of â‰250 rgat only 350 rgfrom the core. This implies that either the bright outer jet layer goes through a very rapid lateral expansion on scales â‰102rgor it is launched from the accretion disk.