How is dark matter like the Hundred Years' War? The war lasted 116 years, and dark matter may not be dark. Conventional wisdom holds that darkness is the whole point of dark matter. Something is pulling stars and gas clouds off course; when astronomers go to look for it, they see nothing that fits the bill, so whatever it is must not emit or absorb light. In fact, if it did respond to light, galaxies would not even exist: the sea of radiation that filled the early universe would have buffeted the matter and kept it from clumping.

Nevertheless, astronomers have speculated for years that dark matter could power certain unexplained sources of light in the cosmos. That interpretation has been controversial--not least because each of these unexplained sources would require a different set of dark particle properties. Now a pair of researchers has found a way to make the dark matter explanation more plausible. "It's an idea that actually unifies these things and can explain everything with one new particle," says astronomer Douglas Finkbeiner of the Harvard-Smithsonian Center for Astrophysics.