Astronomers Discover New Type of Supernova

Until now, it was thought that supernovae always occured in two main varieties, but a team of astronomers are now reporting on the discovery of a new type of supernova called Type Iax.

The research, which was lead by Ryan Foley, Clay Fellow at the Harvard-Smithsonian Center for Astrophysics (CfA), has been accepted for publication in the Astrophysical Journal.

Supernovae were previously divided into either core-collapse or Type Ia categories. Core-collapse supernovae are the explosion of a star about 10 to 100 times as large as our sun, while Type Ia supernovae are the complete disruption of a tiny white dwarf.

The new type of supernovae, Type Iax, is much fainter and less energetic than Type Ia. While both come from exploding white dwarfs, Type Iax supernovas may not completely destroy the white dwarf.

Foley noted:

"A Type Iax supernova is essentially a mini supernova. It's the runt of the supernova litter."

The research team identified 25 examples of the new type of supernova, none of which appeared in elliptical galaxies, which are filled with old stars. This finding suggests that Type Iax supernovas come from young star systems.

The team concluded that based on a variety of observational data, a Type Iax supernova comes from a binary star system containing a white dwarf and a companion star that's lost its outer hydrogen, which leaves it helium dominated. The white dwarf collections helium from the normal star.

Scientists are not sure what triggers a Type Iax, but say it is possible that the outer helium layer ignites first, sending a shock wave into the white dwarf. Alternatively, the white dwarf might ignite first due to the influence of the overlying helium shell. Either way, it looks like in many cases the white dwarf survives the explosion.

The researchers calculate that Type Iax supernovae are about a third as common as Type Ia supernovae, and postulate that the reason that so few have been detected is that the faintest are only one-hundredth as bright as Type Ia supernova.

The Large Synoptic Survey Telescope could potentially discover thousands of Type Iax supernovas over its lifetime.