Peculiar explosions could be a new type of supernova

Artist's impression of the progenitor system of a type Iax supernova. A massive star dumps gas onto a white dwarf companion, forming a hot accretion disk. The extra mass causes a thermonuclear explosion, which may or may not destroy the white dwarf.

Christine Pulliam (CfA)

Supernovae can be divided into two broad categories: those produced by the deaths of very massive stars, and those that involve the explosions of white dwarfs. Within the first category, supernovae vary greatly depending on a number of details, including the mass of the exploding star. On the other hand, white dwarfs seem to all explode in very similar ways, which is why they have proven useful in measuring distances across the Universe.

Beginning in 2002, astronomers started recognizing a peculiar type of explosion. Since then, they've identified 25 of them; they resemble white dwarf supernovas in many respects, but strongly differ in others. A new paper by Ryan J. Foley and colleagues offered an explanation: these were an entirely new type of white dwarf explosion, one involving less energy and more material from a companion star. So much less energy, in fact, that the authors suspect that the white dwarf may not be fully destroyed in these odd events.

In the early days of supernova research, explosions were classified primarily by how much hydrogen and helium they had in their spectra. Type I supernovas, for example, mostly lack both elements. Since stars are mostly composed of hydrogen and helium, that indicates progenitor systems for type I supernovae are unlikely to be exploding stars.