Galaxy-building theory says there are stars and there are stage hands. The bright, shining galaxies filled with stars, the theory goes, took star-building gas from somewhere else, but we couldn't find exactly where the help came from. Now astronomers have likely found that source; starless "dark galaxies" that fed others early in the history of the universe have been seen.
The European Southern Observatory's Very Large Telescope was able to catch a glimpse of the galaxies for the first time as they were being illuminated by a quasar. Since the galaxies are bad at forming stars on their own, they're difficult to see without a light source like a quasar, which shines UV light and can cause a fluorescent glow in the starless galaxies. Their existence has been hinted at before, but this marks the first direct look.