  Blue-supergiant stars develop into core-collapse supernovae --- one of the
most energetic outbursts in the universe --- when all nuclear burning fuel is
exhausted in the stellar core. Previous attempts failed to explain observed
explosions of such stars which have a zero-age main sequence mass of
50~M$_\odot$ or more. Here we exploit the largely uncertain state of matter at
high density, and connect the modeling of such stellar explosions with a
first-order phase transition from nuclear matter to the quark-gluon plasma. The
resulting energetic supernova explosions can account for a large variety of
lightcurves, from peculiar type II to super-luminous events. The remnants are
neutron stars with quark matter core, known as hybrid stars, of about
2~M$_\odot$ at birth. A galactic event of this kind could be observable due to
the release of a second neutrino burst. Its observation would confirm such a
first-order phase transition at densities relevant for astrophysics.
