The journey of galaxy clusters in billions of years

A new study modeled the dynamics and evolution of some of the largest known structures in the universe.

Extragalactic neighborhood. Credit: Wikimedia Commons.

Let’s take a moment to look at our position in the universe.

We are now living on a solar system orbiting the center of the Milky Way galaxy — which itself lies in the Local Group of galaxies neighboring a Local Void, a vast cluster of space with fewer galaxies than expected. Wait, we’re not done yet. These structures are part of a larger region that encompasses thousands of galaxies in a supercluster called the Laniakea Supercluster, which is around 520 million light-years across. 

A group of researchers has now simulated the movement of galaxies in the Laniakea and other clusters of galaxies starting when the universe was in its infancy (just 1.6 million years old) until today. They used observations from the Two Micron All-Sky Survey (2MASS) and the Cosmicflows-3 as the starting point for their study. With these two tools, they looked at galaxies orbiting massive regions with velocities of up to 8,000 km/s — and made videos describing those orbits.

Because the universe is expanding and that influences the evolution of these superclusters, we first need to know how fast the universe is expanding, which has proven to be very difficult to calculate. So the team considered different plausible universal expansion scenarios to get the clusters’ motion. 

Besides Laniakea, the scientists report two other zones where galaxies appear to be flowing towards a gravitational field, the Perseus-Pisces (a 250 million light-years supercluster) and the Great Wall (a cluster of about 1.37 billion light-years). In the Laniakea region, galaxies flow towards the Great Attractor, a very dense part of the supercluster. The other superclusters have similar patterns, the Perseus-Pisces galaxies flow towards the spine of the cluster’s large filament.

The researchers even predicted the future of these galaxies. They estimated the path of the galaxies to something like 10 billion years into the future. It is clear in their videos, the expansion of the universe affecting the big picture. In smaller, denser regions, the attraction prevails, like the future of Milkomeda in the Local Group.

The study has been accepted for publication in Astrophysical Journal.

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