Monster baby galaxies spotted where you would expect them

Monster baby galaxies spotted where you would expect them

Read time: 3 minutes

Elephants are much larger than mice. Little wonder then that baby elephants are also much larger than baby mice. The same is true for galaxies like our own Milky Way. In the course of billions of years, mature galaxies grew from smaller baby galaxies, basically by gobbling up neighbouring gas clouds. And the largest galaxies that we see around us in the current Universe started out as the largest babies.

Using ALMA, Japanese astronomers have now discovered a compact group of nine of those ‘monster baby galaxies’. They are located at a distance of 11.5 billion light-years. This means that their light has taken 11.5 billion years to reach us. In other words: we see those baby galaxies as they were 11.5 billion years ago, when the Universe was still very young, and baby galaxies were all over the place.

In the monstrous baby galaxies, new stars are born at a rate hundreds or thousands of times faster than in our own Milky Way. But because the galaxies contain large amounts of dust, most of the visible starlight is heavily dimmed. As a result, the monster babies are hardly visible with a normal telescope.

Using a smaller Japanese telescope, the astronomers already had detected the submillimeter radiation from the galaxies’ dust, but because of the extremely large distance, they just saw one featureless blob. That’s why they turned to ALMA, which is 10 times as sensitive and has a 60 times sharper vision. It turned out that the featureless blob they had seen before is actually a small cluster of nine monster baby galaxies.


By combining these measurements with observations by the 8.2-meter Subaru Telescope at Mauna Kea, Hawaii, the astronomers discovered something special. The group of monster baby galaxies is located at a place where the density of dark matter in the Universe is much higher than average. Since galaxies are believed to grow around concentrations of dark matter, this is exactly what you would expect – it’s always nice to see your theory confirmed!

Again, the monster baby galaxies are seen as they were 11.5 billion years ago. By now, they will probably have evolved into giant elliptical galaxies, much larger and more massive than our own Milky Way.


The nine monster baby galaxies discovered by the Japanese astronomers are located in a region called SSA22, in the constellation Aquarius the Water-bearer. The first submillimeter observations were carried out with ASTE – the Atacama Submillimeter Telescope Experiment. ASTE is a 10-meter precursor of ALMA, also located at the Llano de Chajnantor in northern Chile.

The observations of the remote monster baby galaxies were carried out by a large group of Japanese astronomers, led by Hideki Umehata of the Japan Society for the Promotion of Science, who at the time was working at the European Southern Observatory in Germany. The results have been published in Astrophysical Journal Letters – a professional astronomy magazine.