  Nova outbursts take place in binary star systems comprising a white dwarf and
either a low-mass Sun-like star or, as in the case of the recurrent nova RS
Ophiuchi, a red giant. Although the cause of these outbursts is known to be
thermonuclear explosion of matter transferred from the companion onto the
surface of the white dwarf, models of the previous (1985) outburst of RS
Ophiuchi failed to adequately fit the X-ray evolution and there was controversy
over a single-epoch high-resolution radio image, which suggested that the
remnant was bipolar rather than spherical as modelled. Here we report the
detection of spatially resolved structure in RS Ophiuchi from two weeks after
its 12 February 2006 outburst. We track an expanding shock wave as it sweeps
through the red giant wind, producing a remnant similar to that of a type II
supernova but evolving over months rather than millennia. As in supernova
remnants, the radio emission is non-thermal (synchrotron emission), but
asymmetries and multiple emission components clearly demonstrate that contrary
to the assumptions of spherical symmetry in models of the 1985 explosion, the
ejection is jet-like, collimated by the central binary whose orientation on the
sky can be determined from these observations.
