  Up to 98% of all single stars will eventually become white dwarfs - stars
that link the history and future evolution of the Galaxy, and whose previous
evolution is engraved in their interiors. Those interiors can be studied using
asteroseismology, utilizing stellar pulsations as seismic waves. The
pulsational instability strips of DA and DB white dwarf stars are pure,
allowing the important generalization that their interior structure represents
that of all DA and DB white dwarfs. This is not the case for the hottest
pulsating white dwarfs, the GW Vir stars: only about 50% of white dwarfs in
this domain pulsate. Several explanations for the impurity of the GW Vir
instability strip have been proposed, based on different elemental abundances,
metallicity, and helium content. Surprisingly, there is a dichotomy that only
stars rich in nitrogen, which by itself cannot cause pulsation driving, pulsate
- the only previous exception being the nitrogen-rich non-pulsator PG 1144+005.
Here, we report the discovery of pulsations in PG 1144+005 based on new
observations. We identified four frequency regions: 40, 55, 97, and 112
day$^{-1}$ with low and variable amplitudes of about 3-6 mmag and therefore
confirm the nitrogen dichotomy. As nitrogen is a trace element revealing the
previous occurrence of a very late thermal pulse (VLTP) in hot white dwarf
stars, we speculate that it is this VLTP that provides the interior structure
required to make a GW Vir pulsator.
