The Great Wall

I was looking through the Center for Astrophysics' website, trying to find an interesting research project for my fifth blog post.  Clicking through the different tabs, I saw a link to the cosmology page and, remembering my fondness for the subject from AY 17, I decided to take a look.  I didn't get too far, though, because I saw a picture labeled "Great Wall" and excited about learning about this part of the universe that never came up in my class on extragalactic astronomy.

The Hercules-Corona Borealis Great Wall is the largest structure in our observable universe, larger even than superclusters by far. It was discovered in 2013 while scientists were mapping gamma ray bursts at high redshifts.  The Great Wall is at a redshift >1, so it's about 3x10$^{_9}$ pc away. 

Before last year, the largest structure in the universe was believed to be the CfA2 Great Wall, located about 6.1x10$^{_7}$ pc away.  Scientists believe its volume to be about 2x10$^{_60}$ cm$^{_3}$.  They can't be certain, though, because part of the Great Wall is near the galactic plane.  Objects near the galactic plane are obscured by the dust and gas of the milky way. 

The existence of Great Walls--these super, super, super, Superclusters-- is such a big deal because it seems to go against the cosmological principle, which says that the universe is homogeneous and isotropic.  In laymen's terms, objects, temperature, chemical composition, and all other characteristics are all evenly distributed throughout the universe.  The fact that there's such a large collection of objects in one place is pretty antithetical to that even distribution.  

They also complicate scientists' ideas of the evolution of the universe.  The Hurcules-Corona Borealis Great Wall is 10 billion light years away, which suggests that the way we see it from Earth now is the way it looked 10 billion years ago, really close to the Big Bang.  Such a large and complicated structure shouldn't have had enough time to form.