Massive ‘Wall’ of Galaxies Has Been Discovered in the Universe

The Universe is not a haphazard dispersion of galaxies placed across an expanding void. The more we get to explore, we see that there are structures, some of which are unfathomably massive clusters and groupings of galaxies that are gravitationally linked. 

Such a structure has just been identified expanding throughout the southern margin of the sky, and it’s a colossus, going across a gigantic 1.37 billion light-years from end to end. Those who discovered it named it ‘the South Pole Wall.’

The Most Massive Discovered Structure Yet

Even though the size of the wall is puzzling, as it is one of the most massive structures in space we’ve ever found, we know what the South Pole Wall is: a galaxy filament, a gigantic formation of galaxies that creates a border between the empty spaces of cosmic voids that together make the cosmic web. Therefore, it can be called a wall.

Other such walls have been previously discovered, including the Hercules-Corona Borealis Great Wall, which is the largest one and spans over 9.7 billion light-years. However, the South Pole Wall​ is rather special because it is incredibly close to the Milky Way galaxy, located only 500 million light-years away from it. Simply put, it is the most massive structure researchers have ever seen this close.

The reason why the gigantic galaxy was not spotted until now is that it was hidden behind what it is known as the Zone of Avoidance or Zone of Galactic Obscuration, which is the Milky Way galactic plane.

This is the disc of our galaxy, a dense area, filled with dust, gas, and stars, which is so thick that it hides a large part of what’s behind it, making that region of the Universe poorly explored in comparison to the rest.

A team of scientists led by cosmographer Daniel Pomarède of the Paris-Saclay University employed a database called Cosmicflows-3, which has distance measurements to almost 18,000 galaxies. These are estimated using redshift, which calculates the velocity of something that’s moving further away based on how extended its light waves are.

Last year, another team of researchers used the same database to measure another parameter, something called peculiar velocity, which is the speed of a galaxy relative to its motion because of the expansion of the Universe.

Using these two parameters, the team was able to calculate the motions of the galaxies relative to each other, and these patterns unveiled the gravitational impact of a much larger mass. Employing algorithms, the team used these motions to map in three dimensions the spreading of material in the South Pole Wall, even further than the Zone of Avoidance.

This Could Have Interesting Implications

The thickest area is located over the South Pole – this zone is the section that is 500 million light-years away. Then it bends north and towards the Earth, coming within 300 million light-years of the Milky Way.

The South Pole Wall. [Image: Pomarède et al., ApJ, 2020]
Along the curving section, the galaxies are moving towards the cluster at the South Pole, and from there, they are shifting towards another massive structure, known as the Shapley Supercluster, which is 650 million light-years away.

Due to the fact that there are areas of the South Pole Wall​ we cannot see, it is possible the structure is even more massive than the team estimated. This finding could have cosmological implications, touching the rate of expansion of the local Universe. It can also help scientists understand the development of our zone, which includes Laniakea, the supercluster of galaxies to which our Milky Way belongs, also identified by Pomarède and his colleagues back in 2014.

The study has been published in The Astrophysical Journal.

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