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.
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.
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