A wide and collimated radio jet in 3C 84 on the scale of a few hundred
  gravitational radii
  Understanding the launching, acceleration, and collimation of jets powered by
active galactic nuclei remains an outstanding problem in relativistic
astrophysics. 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 transverse jet
structure in the acceleration and collimation zone of only two sources. Here we
report radio interferometric observations of 3C 84 (NGC 1275), the central
galaxy of the Perseus cluster, made with an array including the orbiting radio
telescope of the RadioAstron mission. The obtained image transversely resolves
the edge-brightened jet in 3C 84 only 30 microarcseconds from the core, which
is ten times closer to the central engine than what has been possible in
previous ground-based observations, and it allows us to measure the jet
collimation profile from ~ 100 to ~10000 gravitational radii from the black
hole. The previously found, almost cylindrical jet profile on scales larger
than a few thousand r_g is now 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 larger
than about 250 r_g at only 350 r_g from the core. If the bright outer jet layer
is launched by the black hole ergosphere, it has to rapidly expand laterally on
scales smaller than 100 r_g. If this is not the case, then this jet sheath is
likely launched from the accretion disk.
