Astronomers have identified a white dwarf star in our galaxy that may be the leftover remains of a recently discovered type of supernova. The properties of this unusual white dwarf, known as LP 40-365, may help scientists determine how such unusual supernovae are created, say Stephane Vennes and colleagues. A common group of exploding stars, known as Type Ia supernovae, have a fairly uniform brightness that makes them useful for cosmology.

Type Ia supernovae are caused by the complete destruction of a white dwarf star in a thermonuclear explosion. Recently, astronomers have discovered a related form of supernova, called Type Iax, which look like Type Ia, but are much fainter. Type Iax supernovae may be caused by the partial destruction of a white dwarf star in such an explosion. If that interpretation is correct, part of the white dwarf should survive as a leftover object.

The scientists have identified LP 40-365 as an unusual white dwarf with a low mass, high velocity and strange composition - exactly as might be expected for the leftover star from a Type Iax event. They calculate that the explosion must have occurred between five and 50 million years ago.