ScienceDaily (Nov. 6, 2009) — An unusual supernova rediscovered in seven-year-old data may be the first example of a new type of exploding star, possibly from a binary star system where helium flows from one white dwarf onto another and detonates in a thermonuclear explosion.

Artist’s impression of an AM-CVn star system, where helium flows from one star, a helium white dwarf (upper right), onto another, piling up in an accretion disk around a small, dense primary star. Helium from the disk eventually falls onto the star, forming a shell that may end up exploding as a Type .Ia (point one A) supernova. (Credit: Tony Piro)

In a paper first published online Nov. 5 in the journal Science Express, University of California, Berkeley, and Lawrence Berkeley National Laboratory (LBNL) astronomer Dovi Poznanski and his colleagues describe the outburst, dubbed SN 2002bj, and why they believe it is a new type of explosion.

"This is the fastest evolving supernova we have ever seen," said Poznanski, a UC Berkeley post-doctoral fellow who recently joined LBNL’s Computational Cosmology Center. "It was three to four times faster than a standard supernova, basically disappearing within 20 days. Its brightness just dropped like a rock."

This rapid drop, coupled with the supernova’s faintness, the strong signature of helium in the spectrum of the explosion, the absence of hydrogen, and the possible presence of vanadium — an element never previously identified in supernova spectra — points toward helium detonation on a white dwarf, the astronomers said.

"We think this may well be a new physical explosion mechanism, not just a minor variation of ones already known," said co-author Alex Filippenko, UC Berkeley professor of astronomy. "This supernova is qualitatively different from the complete disruption of a white dwarf, known as a Type Ia supernova, or the collapse of an iron core and rebound of the surrounding material, so-called ‘core-collapse supernovae.’"

Co-author Joshua Bloom, UC Berkeley associate professor of astronomy, also views SN 2002bj as a "new beast" quite different from the two well-known classes of supernovae.

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