Key takeaways

  • The South Pole Wall is a gigantic galaxy filament stretching 1.37 billion light years.
  • It’s the largest structure we’ve seen close to the Milky Way, only 500 million light-years away.
  • It was hidden behind the Milky Way’s dense and luminous disc, known as the Zone of Avoidance.
  • Astronomers used galaxy movements and redshift data to map this colossal structure.
  • Understanding the South Pole Wall may help explain local universe expansion and the Hubble Tension.

The Universe is not just a random collection of galaxies scattered over an expanding nothingness. The closer we look, the more we notice structures, some of which are incomprehensibly large groups and clusters of galaxies held together by gravity.

Such a structure has recently been spotted arcing across the southern tip of the sky, and it is a colossus, stretching 1.37 billion light years from end to end. Its discoverers termed it the South Pole Wall.

Although the magnitude is impressive (it’s one of the largest structures in space we’ve ever seen), we know exactly what the South Pole Wall is. It’s a galaxy filament, a massive collection of galaxies that serves as a boundary between the empty areas of cosmic voids that make up the cosmic web. Hence, we call it a wall.

Other, larger, similar walls are known. The Hercules-Corona Borealis Great Wall is the greatest, spanning 9.7 billion light-years. But the South Pole Wall is unique because it is so close to the Milky Way galaxy, only 500 million light-years distant. In other words, it is the largest building we have ever observed up close.

You’re undoubtedly asking how on Laniakea we missed one of the Universe’s greatest galaxy filaments sitting in front of us. And there is a very excellent answer to that question: it was hidden behind the Milky Way galactic plane, often known as the Zone of Avoidance or Zone of Galactic Obscuration.

This is our galaxy’s disc, which is thick and luminous with dust, gas, and stars. It’s so dense and dazzling that it obscures most of what’s behind it, leaving that section of the Universe underexplored in comparison to the rest.

If the Zone of Avoidance was so good in concealing the South Pole Wall, how did astronomers discover it? The explanation is a little more complex, but it all comes down to how galaxies migrate around the sky.

A team of researchers lead by cosmographer Daniel Pomarède of Paris-Saclay University used Cosmicflows-3, a database including distance calculations for over 18,000 galaxies. These are calculated using redshift, which estimates how quickly something moves away depending on how stretched out its light waves are.

Last year, a different team of researchers utilized this information to determine another characteristic, something known as peculiar velocity, which is the velocity of a galaxy relative to its motion caused by the expansion of the Universe.

The team used these two quantities to compute the galaxies’ relative speeds, which revealed the gravitational effect of a considerably larger mass. Using algorithms, the team was able to map the distribution of material in three dimensions on the South Pole Wall, even beyond the Zone of Avoidance.

The densest area is over the South Pole, 500 million light-years away. Then it turns north and approaches us, passing within 300 million light-years of the Milky Way.

The galaxies are migrating along the curved arm towards the clump at the South Pole, and from there to another huge structure, the Shapley Supercluster 650 million light-years away.

Because we can’t view parts of the South Pole Wall, the construction could be substantially greater than we think. But we can be certain that astronomers are eager to find out.

For starters, it may have interesting cosmological consequences, influencing the pace of expansion of the local Universe. This may or may not have an impact on the Hubble Tension, which is the difference between the rate of expansion in the local Universe and the rate of expansion in the early universe.

It can also help us comprehend the evolution of our local space, which includes Laniakea, the supercluster of galaxies to which the Milky Way belongs, which was found by Pomarède and his colleagues (headed by Brent Tully of the University of Hawai’i at Manoa).

This is an incredible discovery, and we can’t wait to see what else it reveals.

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