SN 2002bj was the explosion of a star in the galaxyNGC 1821[fr], located in the constellationLepus.[3] 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[4] and was categorized as a Type IIn supernova.[5]
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.[6]
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.[6] In this sense, it was akin to a nova explosion, although the magnitude of the explosion was a thousand times greater.[3] In 2007 Lars Bildstenet al. had predicted this category of explosion would occur in AM Canum Venaticorum star binary systems.[7]
