What are the Galactic Walls?

Astronomers are always looking for the “most distant” galaxies, the “most energetic” stellar explosions and the “most massive” stars. But what about the biggest cosmic walls?

I want you to imagine the greatest collection of galaxies possible. Now double it. No, triple it. Can you see it? Yep, that’s a galactic wall. Well, OK, these aren’t walls of bricks and mortar; they’re walls of galaxies cemented together by dark matter. They are the biggest structures in the universe that we know of.

And. They. Are. HUGE.

galactic wall

But what are they exactly? Well, nearly 14 billion years ago, our universe exploded from a single point, spewing matter and energy to form the rapidly expanding universe we know and love. All the matter in the universe splattered and condensed into long web-like filaments of dark matter, along which galaxies gravitationally attached themselves. As the universe cooled and matured, a 3-dimensional web of galaxies formed, composed of both these long filaments and vast bubble-like voids.

Along these filaments, dense superclusters of galaxies settled – this is what we call “galactic walls.” And perhaps the most famous galactic wall is the Sloan Great Wall that was discovered by the Sloan Digital Sky Survey – or SDSS – in 2003. It’s basically a huge collection of galaxies about 1 billion light-years from Earth, spanning over 1.4 billion light-years across (it, therefore, takes light 1.4 billion years to travel from one end to the other).

Though impressive, the Sloan Great Wall is no longer the biggest, but it remains the most famous. Since 2003, bigger galaxy walls have been detected, but this year, the biggest wall of all has been claimed.

When studying a collection of distant galaxies between 4.5 and 6.4 billion light-years away, astronomers realized that over 800 of them occupy the same cosmic filament, a volume ten times that of the Sloan Great Wall. They called it the BOSS Great Wall – after the Baryon Oscillation Spectroscopic Survey, a project also run by the SDSS. BOSS is designed to study the distribution of galaxies throughout the cosmos, in an effort to understand how fast the universe is expanding and how galaxies move in relation to one another.

Though impressive, these Great Walls may not actually be the greatest of them all. For starters, records are made to be broken, and bigger walls could be discovered in the future as surveys get more and more sensitive. Also, there’s a large swathe of sky BEHIND our galaxy called the “Zone of Avoidance” that astronomers cannot see — it’s a region of sky the Milky Way’s core and disk is blocking from view. So there could be the mother of all walls that we’ll never observe.

So why do we care about these huge walls of galaxies besides the fact we love big things in space, and we love breaking records?

Well, according to the “cosmological principle,” all matter in the universe, when viewed on a large enough scale, should appear more or less uniform, and the largest structures shouldn’t exceed 1.2 billion light-years across. This is based on a mathematical theory put forth by none other than Isaac Newton.

A possible galactic wall measuring over 1.2 billion light years across could mean that our understanding of the universe is incomplete or incorrect. And there are clues that there are even bigger structures out there.

So what do you think is going on? Is our understanding of the universe flawed? Let us know in the comments!

Leave a Reply