Hubble Celebrates Its 32nd Birthday With A Group Of 5 Galaxies

As well as being a neat image, collecting data on such a densely packed group of galaxies can help astronomers learn about dark matter. Normally, dense groups of galaxies are found in the center of enormous galaxy clusters, but this particular group is out on its own, relatively far from other galaxies. Researchers think this might be because these galaxies are hosting a large amount of dark matter.

Dark matter is a mysterious substance, as physicists know that it must exist based on the movement of galaxies – in fact, it is not only present in our universe, but also makes up more than a quarter of the mass of everything that exists. With that said, dark matter can’t be detected directly (via Digital Trends). In the case of HCG 40, there could be a large amount of dark matter around the five galaxies, forming a large cloud around them. This cloud provides resistance that slows the movement of the individual galaxies and binds them together.

Studying unusually dense galaxy groups like this can also help astronomers understand how galaxies formed and evolved. “I remember seeing this on a sky survey and saying, ‘Wow look at that!'” said Paul Hickson, an astronomer at the University of British Columbia, Vancouver, who rediscovered this group while looking through a sky atlas from the 1960s. “All that I was using at the time was a big plastic ruler and a magnifying glass while looking over sky survey prints.”