The 2011 Nobel Prize in Physics was awarded for groundbreaking use of supernovae to measure the expansion of the universe, which yielded a surprise: it’s accelerating, not slowing down. Nevertheless, astronomers have been unsure what type of explosion produces these bright supernovae. A new study using the Subaru Telescope suggests that Type Ia supernovae come from the merger of two white dwarfs, not one white dwarf grown fat by feeding off its companion.