A group of astronomers believe they have found a new kind of "mini" supernovae that appear to share traits with other previously known types.
Until now, only core-collapse supernovae, the grand finale of stars approximately 10 to 100 times more massive than our sun, and Type Ia, which occur when certain conditions exist in binary (two-star) systems, were known to exist.
(Because of their highly predictable luminosity, Type Ia supernovae have long been used as "standard candles," much like distant lighthouses, to measure the distances to the galaxies.)
The new type, known as Type Iax, are fainter, less energetic and rarer than their cousins, write Ryan J. Foley, et. al in an upcoming edition of The Astrophysical Journal.
"A Type Iax supernova is essentially a mini supernova," says Foley, who is Clay Fellow at the Harvard-Smithsonian Center for Astrophysics. "It's the runt of the supernova litter."
The team has identified 25 examples of the new type of supernova. Compared to the already rare Type Ia supernovae, the new type is rarer still, according to the researchers.
"None of them appeared in elliptical galaxies, which are filled with old stars. This suggests that Type Iax supernovas come from young star systems," according to the Carnegie Institution for Science, where three of the paper's co-authors, Wendy Freedman, Mark Phillips and Eric Persson, hail.
But, like Type Ia supernovae, Type Iax also occur in binary star systems.
The Carnegie Institution for Science says:
"Based on a variety of observational data, the team concluded that a Type Iax supernova comes from a binary star system containing a white dwarf and a companion star that has lost its outer hydrogen, leaving it helium dominated. The white dwarf collects helium from the normal star.
"Researchers aren't sure what triggers a Type Iax. It's 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."
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