Without the quasar’s natural flashlight, the dark galaxies would otherwise have remained unseen. Zeroing in on those galaxies, what the team of astronomers did see, were low-mass regions of space roughly 16,500 to 19,800 light years across (roughly one-fifth the size of the Milky Way) each with amounts of gas (mostly hydrogen) about one billion times more massive than our Sun.

As dark galaxies reside in our roiling universe, they are not destined to remain hidden, or even around at all. In fact, they may serve as fuel for more conventional, star-studded galaxies.

“In our current theory of galaxy formation, we believe that big galaxies form from the merger of smaller galaxies. Dark galaxies bring to big galaxies a lot of gas, which then accelerates star formation in the bigger galaxies,” Sebastiano Cantalupo, a Research Team Leader at the Institute for Astronomy, ETH Zurich, told the Kavli Foundation.