Astronomers discover new class of supernova
http://www.globalpost.com/dispatch/news/science/130326/astronomers-discover-new-class-supernova

US astronomers say they’ve discovered a new class of supernova that doesn’t fit in the two previously known categories.
The new class of supernova has been dubbed Type Iax.
Astronomers had previously divided supernovae into two types, known as core-collapse and Type Ia. Core-collapse supernovae are the explosion of a star about 10 to 100 times the size of the sun, while Type Ia supernovae are the complete explosion of a tiny white dwarf.

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> that doesn’t fit in the two previously known categories.

Previously known categories include:
Ia, Ib, Ic, Ib/c, II-P, II-L, IIN, IIB, II-P/L, II-P/L/N

“The new Type Iax class of supernova is fainter and less energetic than the Type Ia and is thought to be the result of a white dwarf star explosion, which did not destroy the star entirely.

“A Type Iax supernova is essentially a mini supernova,” lead study author Ryan Foley of the Harvard-Smithsonian Center for Astrophysics said. “It’s the runt of the supernova litter.”

“Type Iax supernovae are about one-hundredth as bright as other supernovae and are around a third as common as the Type Ia supernovae. The new class of supernova is also thought to come from young star systems, as it was not found in elliptical galaxies, which are filled with older stars.

“Foley and his colleagues identified 25 examples of the new type of supernova.

This really is fascinating, a supernova-like event that does not destroy the star entirely is known as a “supernova impostor”.
en.wikipedia.org/wiki/Supernova_impostor
The Eta Carinae explosion was a supernova impostor. Like the new type these supernova impostors, the original ones are considerably fainter than most, but in the past the ones I know of had type IIp, so Iax is quite different.