Not all galaxies are filled with stars. Astronomers have discovered a horde of nearly starless galaxies each about the size of the Milky Way. How they formed is a mystery, and they imply that there are more ways for a galaxy to evolve than previously imagined.
Pieter van Dokkum, an astronomer at Yale University, and colleagues stumbled across 47 galaxies that stopped forming stars long ago. The stars in each galaxy that remain— about 0.1 percent of the number in the Milky Way — are spread throughout a sphere roughly the size of a typical spiral galaxy. A stargazer living in one of these galaxies might see only a few stars at night, says van Dokkum. “You need something unusual to create a galaxy like this.”
