Pair-Instability Explosions: observational evidence
  It has been theoretically predicted many decades ago that extremely massive
stars that develop large oxygen cores will become dynamically unstable, due to
electron-positron pair production. The collapse of such oxygen cores leads to
powerful thermonuclear explosions that unbind the star and can produce, in some
cases, many solar masses of radioactive 56Ni. For many years, no examples of
this process were observed in nature. Here, I briefly review recent
observations of luminous supernovae that likely result from pair-instability
explosions, in the nearby and distant Universe.
