Astronomers studying a rare supernova were stunned to find a mysterious companion object about two light weeks away, the presence of which they are having difficulty explaining. The discovery concerning Supernova 1987a was made by astronomers with the Harvard-Smithsonian Center for Astrophysics at the Cerro-Tololo Inter-American Observatory in Chile. "If it's an object that was thrown out by the supernova explosion, then . . . it traveled at half the speed of light, which is one of the things that scared us about it. We didn't believe that anything really massive could be traveling at that speed," said one astronomer.