To understand how galaxies interact in today’s universe, we need to look at the distant past, and now astronomers have observed an ancient galaxy cluster just about to form.

Using telescopes in Arizona and Hawaii, an international team of physicists observed a “proto-cluster” forming about 1.7 billion years after the Big Bang with the mass of a quadrillion Suns. The team detected 953 galaxies that appear to be clumping up in the same area of the sky, and the astronomers were able to confirm that at least 65 of them are actually coming together.

“Many of the faint galaxies in this patch lie at the same distance,” said Dr. Arjun Dey, lead author of the study, in a statement.

“They are clumped together due to gravity and the evidence suggests that the cluster is in the process of forming.”  

Galaxies in the universe are not distributed randomly, but their location depends significantly on the gravity of the objects around them. There are galaxies all alone while others, like the Milky Way, are in groups. The denser groups are the clusters, with some of them having a combined mass of a million billion (quadrillion) Suns.

“The protocluster will very likely grow into a massive cluster of galaxies like the Coma cluster, which weighs more than a quadrillion suns,” said Dr. Kyoung-Soo Lee, the discoverer of the protocluster and co-author of the study, which is published in The Astrophysical Journal.

The formation and infancy of these clusters are not completely clear yet, but the discovery of protoclusters can help understand how these complex giant structures come to form. Understanding how clusters form provides clues to the evolution of the universe as a whole. The size and number of galaxy clusters depends on the rate of expansion of the universe as well as the matter content of the universe.

While the discovery of such a distant and massive cluster is fascinating, to truly understand clusters like this we need to observe many more. With this goal in mind, the team is now observing larger areas of the sky in the hope of finding many more of these protoclusters.