Dark Galaxies Finally Spotted

Ultraviolet light from a quasar (in red circle) causes hydrogen gas in dark galaxies (blue circles) to glow, making the dark galaxies detectable. (Photo : ESO)

Scientists have peered so far into our universe that they have literally gone back in time. For the first time, astronomers have viewed so-called dark galaxies which are some of the earliest objects in our universe.

Dark galaxies are small, gas-rich galaxies from the universe's early periods that were simply inefficient at forming stars. It is thought that the gas from these galaxies is what gave birth to the star-filled galaxies that we observe today.

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Because they never really formed many stars, these galaxies are dim and hard to spot. After years of trying out many techniques, it seems that the simplest solution won out in the end.

"Our approach to the problem of detecting a dark galaxy was simply to shine a bright light on it," explains Simon Lilly, co-author of the paper. "We searched for the fluorescent glow of the gas in dark galaxies when they are illuminated by the ultraviolet light from a nearby and very bright quasar. The light from the quasar makes the dark galaxies light up in a process similar to how white clothes are illuminated by ultraviolet lamps in a night club."

Using this technique, scientists identified around 100 gaseous objects within a few million light-years of the bright quasar HE 0109-3518. After analysis, the team narrowed down their findings to just 12. These objects are the most definitive evidence of dark galaxies ever found.

"Our observations with the VLT (Very Large Telescope) have provided evidence for the existence of compact and isolated dark clouds. With this study, we've made a crucial step towards revealing and understanding the obscure early stages of galaxy formation and how galaxies acquired their gas," concludes lead-author Sebastiano Cantalupo.