  Hubble Space Telescope} images of the ejecta surrounding the nova T Pyxidis
resolve the emission into more than two thousand bright knots. We simulate the
dynamical evolution of the ejecta from T Pyxidis during its multiple eruptions
over the last 150 years using the adaptive mesh refinement capability of the
gas dynamics code Ramses. We demonstrate that the observed knots are the result
of Richtmeyer-Meshkov gas dynamical instabilities (the equivalent of
Rayleigh-Taylor instabilities in an accelerated medium). These instabilities
are caused by the overrunning of the ejecta from the classical nova of 1866 by
fast moving ejecta from the subsequent six recurrent nova outbursts. The model
correctly predicts the observed expansion and dimming of the T Pyx ejecta as
well as the knotty morphology. The model also predicts that deeper, high
resolution imagery will show filamentary structure connecting the knots. We
show reprocessed Hubble Space Telescope imagery that shows the first hints of
such structure.
