  Active galactic nuclei (AGN) accreting at rates close to the Eddington limit
can host radiatively driven mildly relativistic outflows. Some of these X-ray
absorbing but powerful outflows may produce strong shocks resulting in a
significant non-thermal emission. This outflow-driven radio emission may be
detectable in the radio-quiet quasar PDS 456 since it has a bolometric
luminosity reaching the Eddington limit and a relativistic wide-aperture X-ray
outflow with a kinetic power high enough to quench the star formation in its
host galaxy. To investigate this possibility, we performed very-long-baseline
interferometric (VLBI) observations of the quasar with the European VLBI
Network (EVN) at 5 GHz. The EVN image with the full resolution reveals two
faint and diffuse radio components with a projected separation of about 20 pc
and an average brightness temperature of around two million Kelvin. In relation
to the optical sub-mas-accuracy position measured by the Gaia mission, the two
components are very likely on opposite sides of an undetected radio core. The
VLBI structure at the deca-pc scale can thus be either a young jet or a
bidirectional radio-emitting outflow, launched in the vicinity of a strongly
accreting central engine. Two diffuse components at the hecto-pc scale, likely
the relic radio emission from the past AGN activity, are tentatively detected
on each side in the low-resolution EVN image.
