  T Pyxidis is the prototypical recurrent nova (RN) with a mysterious nova
shell. We report new observations of the shell with HST. The knots in the shell
are expanding with velocities 500-715 km/s, for a distance of 3500 pc. The
fractional expansion of the knots is constant, and this implies no significant
deceleration. Hence, the knots were ejected by an eruption close to the year
1866. Knots have turned on after 1995, and this demonstrates that the knots are
powered by shocks from the collision of the 1866 ejecta with fast ejecta from
later RN eruptions. The 1866 ejecta has a total mass of 10^-4.5 Msun, which
with the low ejection velocity shows that the 1866 event was an ordinary nova
eruption, not a RN eruption. The accretion rate before the ordinary nova event
must have been low (around the 4x10^-11 Msun/yr expected for gravitational
radiation alone) and the matter accumulated on the surface of the white dwarf
for ~750,000 years. The current accretion rate (>10^-8 Msun/yr) is 1000X higher
than expected for a system below the period gap, with the plausible reason
being that the 1866 event started a continuing supersoft source that drives the
accretion. A key fact about T Pyx is that its accretion rate has been secularly
declining since before the 1890 eruption, with the current rate being only 3%
of its earlier rate. The decline in the observed accretion rate shows that the
supersoft source is not self-sustaining, and we calculate that the accretion in
T Pyx will effectively stop in upcoming decades. With this, T Pyx will enter a
state of hibernation, lasting for an estimated 2,600,000 years, before
gravitational radiation brings the system into contact again. Thus, T Pyx has
an evolutionary cycle going from an ordinary CV state, to its current RN state,
to a future hibernation state, and then repeating this cycle.
