When thinking about how galaxies form, scientists have speculated about large masses of gas that are drawn together to form a kind of embryonic proto-galaxy. But because these supposed objects are starless, they would be practically invisible, thus making them impossible to detect — or so it would seem.
Now, thanks to an innovative process of illuminating distant regions of space, astronomers have finally found the "dark galaxies" they were looking for.
Indeed, what better way to find a dark object than by shining a light on it — and this is exactly what the astronomers have done. By taking advantage of the ultraviolet light emitted by a nearby and very bright quasar, they were able to detect the fluorescent glow of the gas in the dark galaxies. It's akin to how your white shirt lights up from ultraviolet lights when you play glow-in-the-dark mini golf.
Andrew Fazekas of National Geographic explains how it was done:
A superbright galaxy 11 billion light-years away, the quasar shines with the power of a hundred trillion suns and can light up its galactic neighborhood to a radius of ten million light-years. Quasars are very distant galaxies that have actively feeding-and rapidly rotating-supermassive black holes at their hearts.
Using the European Southern Observatory's Very Large Telescope (VLT) in Chile, the astronomers took a very long exposure snapshot of the area surrounding the quasar and detected at least a dozen dark-galaxy candidates.
Only by combining the light-gathering power and exquisite sensitivity of the VLT's four 8.2-meter telescopes could the team directly observe the dim galaxies.
Now, because we're looking back in time by a factor of 11 billion years, the objects offer a unique opportunity to see galaxies in the making. They are quite literally at their earliest stage of evolution, when their various compositions and configurations aren't yet amenable to the formation and sparking of stars. Consequently, the scientists are referring to their discovery as "the missing link."
This research was conducted by Sebastiano Cantalupo, Simon Lilly, and Richard Hook. Their paper will soon appear in a future edition of Monthly Notices of the Royal Astronomical Society.
Image courtesy of National Geographic.