Astronomers have detailed theories about what type of stars self-destruct in titanic supernova explosions. However, it would be useful to test stellar theory by actually seeing what a doomed star looked like before it blew apart. The problem is that a supernova blast pretty much eradicates all evidence of what the progenitor star was. Like a surveillance camera photographing the scene of a crime before it happened, the Hubble Space Telescope has a priceless archival photo of the galaxy that contains a picture of the supernova progenitor star as it appeared eight years before it exploded. The progenitor was comparatively easy to find because it was one of the brightest stars in the host galaxy. But the discovery has only further confounded supernova mysteries. The progenitor star belongs to a class of luminous blue variable stars that are not expected to explode at such an early stage of their existence.
http://hubblesite.org/news_release/news/2009-13