Galaxies are like cities of stars in the Universe. However, astronomers have recently discovered 12 galaxies that are more like ghost towns, as there are almost no stars living there!
These small galaxies are called ‘dark galaxies’, as they don’t have any starlight to make them shine brightly. Astronomers had expected dark galaxies to exist, because they play an important role in how they think galaxies have grown and evolved during the history of the Universe. But, until this new discovery, nobody had ever seen one.
Dark galaxies are very far away in the Universe. They are thought to be the ‘building blocks’ that helped to create the big star-filled galaxies that we see today, like our own Milky Way Galaxy. We can still see these ‘building blocks’, even though they have already been used to help construct the big galaxies. This is because when we observe the distant Universe, we are looking into the past! (To learn more about how astronomers can look back in time, click here.)
But how could astronomers look for a galaxy that is dark? (Imagine looking for a candle in a dark room – blow out the flame and it would be difficult to find.) “Simply shine a bright light on it,” explains Simon Lilly, one of the astronomers behind the new discovery. That’s why the astronomers looked for dark galaxies around incredibly bright galaxies called ‘quasars’, which are also very far away. “The light from the quasar makes the dark galaxies light up,” says Simon.
These dark galaxies might be small compared to the galaxies that we see today, but they still contained about 1 billion times as much gas as the Sun!