  Supermassive black holes at the centre of active galactic nuclei power some
of the most luminous objects in the Universe. Typically, very long baseline
interferometric (VLBI) observations of blazars have revealed only funnel-like
morphologies with little information of the ejected plasma internal structure,
or lacked the sufficient dynamic range to reconstruct the extended jet
emission. Here we show microarcsecond-scale angular resolution images of the
blazar 3C 279 obtained at 22 GHz with the space VLBI mission RadioAstron, which
allowed us to resolve the jet transversely and reveal several filaments
produced by plasma instabilities in a kinetically dominated flow. Our high
angular resolution and dynamic range image suggests that emission features
traveling down the jet may manifest as a result of differential
Doppler-boosting within the filaments, as opposed to the standard shock-in-jet
model invoked to explain blazar jet radio variability. Moreover, we infer that
the filaments in 3C 279 are possibly threaded by a helical magnetic field
rotating clockwise, as seen in the direction of the flow motion, with an
intrinsic helix pitch angle of ~45 degrees in a jet with a Lorentz factor of
~13 at the time of observation.
