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SN 2002bj was the explosion of a star in the galaxy NGC 1821, located in the constellation Lepus. The explosion was discovered by Jack Newton in scans of images produced by Tim Puckett. (It was independently discovered by the Lick/Tenagra Observatory as part of their combined supernova search program.) Initially it had an apparent magnitude of about 14.7 and was categorized as a Type IIn supernova. However, in 2008 Dovi Poznanski discovered that the spectrum more closely resembled a Type Ia supernova. Further, the energy output was much lower than a typical supernova and the luminosity dropped at a dramatic pace.
A team consisting of Poznanski, Joshua Bloom, Alex Filippenko and others concluded that it was a new category of exploding star. This system is believed to consist of a binary pair of white dwarf stars, with helium being transferred from one dwarf to the other. The accreted helium exploded in a thermonuclear reaction on the surface of the more massive white dwarf, resulting in the observed outburst. In this sense, it was akin to a nova explosion, although the magnitude of the explosion was a thousand times greater. In 2007, Lars Bildsten et al. had predicted this category of explosion would occur in AM Canum Venaticorum-type binary systems.
- Sanders, Robert. "Rapid supernova could be new class of exploding star". UC Newsroom (University of California, Berkeley). Retrieved 2009-11-06.
- Bishop, David (Apr 26, 2002). "Supernova 2002bj in NGC 1821". Astronomy Section, Rochester Academy of Science. Retrieved 2009-11-06.
- Matheson, T.; Berlind, P. (March 2002). "Supernova 2002bj in NGC 1821". IAU Circulars 7844 (5). Bibcode:2002IAUC.7844....5M.
- Siegel-Itzkovich, Judy (November 5, 2009). "US-Israeli team's speedily evolving supernova seems to be a new class of exploding star". The Jerusalem Post. Retrieved 2009-11-06.
- Bildsten, Lars; Shen, Ken J.; Weinberg, Nevin N.; Nelemans, Gijs (June 2007). "Faint Thermonuclear Supernovae from AM Canum Venaticorum Binaries". The Astrophysical Journal 662 (2): L95–L98. arXiv:astro-ph/0703578. Bibcode:2007ApJ...662L..95B. doi:10.1086/519489.
- "NED results for object NGC 1821". NASA/IPAC Extragalactic Database. Retrieved 2009-11-06.