A supernova is a powerful explosion at the end of the life of many stars. All massive stars with an initial mass greater than eight solar masses will eventually be torn apart by a supernova, but that fate also awaits smaller stars that are unlucky enough, after their actual end as a white dwarf, to accrete more material from a partner star, with which they form a binary system. Without supernovae, there would be no life, because it’s the only way heavy elements can be spread around the cosmos.
On the whole, this process is understood. Particularly energetic supernovae, however, still attract the attention of astronomers, because some of them are still hiding a few secrets. One of these is pair-instability supernovae, which can involve stars that are greater than 64 solar masses and are particularly poor in elements heavier than helium, or stars greater than 140 solar masses, if these are normal main-series stars of the current generation. These supernovae tear apart the star completely, there’s not even a black hole left – thus, they also produce a lot of energy. The term “pair instability” comes from the fact that, in these stars, temperature (billions of degrees) and density are so high that photons from gamma radiation produced by fusion are transformed into electron-positron pairs. This, however, reduces the radiation pressure, and the star collapses on itself like air being let out of a balloon.