Cosmic walls

Q: What are cosmic walls?

Krishna: Galaxies form massive wall-like structures in the far reaches of our universe.

One such example of a cosmic wall was  discovered  by Astronomers  (1) on the southern border of the local cosmos and  reported evidence for what may be walls of galaxies as far as 8 billion light-years away, indicating that matter formed distinct structures earlier in the universe's history than many scientists expected.

The South Pole Wall, as it is known, consists of thousands of galaxies — beehives of trillions of stars and dark worlds, as well as dust and gas — aligned in a curtain arcing across at least 700 million light-years of space. It winds behind the dust, gas and stars of our own galaxy, the Milky Way, from the constellation Perseus in the Northern Hemisphere to the constellation Apus in the far south. It is so massive that it perturbs the local expansion of the universe.

 The entire conglomeration is behind the Milky Way, in what astronomers quaintly call the zone of avoidance. The galaxies in the wall cannot be seen, but  scientists were able to observe their gravitational effects by assembling data from telescopes around the world.

There is a list of largest cosmic structures discovered till now.  The list includes superclusters, galaxy filaments and large quasar groups (LQGs). The list characterizes each structure based on its longest dimension (2).

In the expanding universe, as described in 1929 by the astronomer Edwin Hubble and confirmed for almost a century, distant galaxies are flying away from us as if they were dots on an inflating balloon; the farther they are, the faster they recede from us, according to a relation called the Hubble law.

That motion away from Earth causes their light to be shifted to longer, redder wavelengths and lower frequencies, like retreating ambulance sirens. Astronomers use this “redshift,” which is easily measured, as a proxy for relative distance in the universe. By measuring the galaxy distances independently astronomers  were able to distinguish the motion caused by the cosmic expansion from motions caused by gravitational irregularities.

As a result, they found that the galaxies between Earth and the South Pole Wall are sailing away from us slightly faster than they otherwise should be, by about 30 miles per second, drawn outward by the enormous blob of matter in the wall. And galaxies beyond the wall are moving outward more slowly than they otherwise should be, reined in by the gravitational drag of the wall.

Astronomers have found that galaxies are gathered, often by the thousands, in giant clouds called clusters and that these are connected to one another in lacy, luminous chains and filaments to form superclusters extending across billions of light-years. In between are vast deserts of darkness called voids.

However, some astrophysicists say it's too soon to say that the clustered redshifts represent walls, filaments, or clusters of galaxies because the scientists only looked at a very narrow piece of sky. Nevertheless, comparing the structures very far out in space--and far back in time--with those closer to our neighborhood will help scientists develop more accurate models of how our universe has evolved.

Footnotes:

1. https://iopscience.iop.org/article/10.3847/1538-4357/ab9952

2. https://en.wikipedia.org/wiki/List_of_largest_cosmic_structures