11 Mar 2016
Astronomers just observed the biggest collection of star stuff that we’ve seen so far.
An international team of scientists described a huge wall of galaxies in a little-explored part of the cosmos. It’s over a billion light years long, bristling with 830 galaxies. They have dubbed it the BOSS Great Wall, named after the BOSS survey which spotted it.
At the largest scale, matter in the universe forms long threads and dense clusters—like a net with big knots. Between the threads are voids drained of almost all matter. In 2014, astronomers learned that our Milky Way galaxy is just one of many in the Laniakea supercluster, which is a web of 100,000 galaxies.
But superclusters can stick together and form even bigger structures. The BOSS Great Wall is a tight network of four superclusters. The largest two form a stretched-out wall of galaxies that’s about 1.2 billion light years long. This is one of only a few supercluster systems ever found. Only one other system, the Sloan Great Wall, comes close in size, but not quite close enough—BOSS has over twice as many galaxies and is 170% wider than Sloan.
“It looks like we have a structure that is bigger than anything else: like two Sloan Great Wall scale structures right next to each other,” said Heidi Lietzen of the Institute of Astrophysics at the University of La Laguna in Spain, who was the lead author of the new study. “The question now is: is it too big for our cosmological theories?”
Scientists are still figuring out what shapes supercluster systems like this one can take, said Elmo Tempel, an astronomer at the Tartu Observatory in Estonia and a co-author on the study. Since they’ve only found a few systems of this scale, astrophysicists aren’t sure whether they always form wall-like structures or if the one’s they’ve seen are special cases. The next step is to run simulations of the shapes that superstructures this massive tend to form, Tempel said.
Superclusters have their origins in pools of dark matter that formed early in the universe’s history, said Brent Tully of the Institute for Astronomy at the University of Hawaii. Normal matter flows towards the wells of dark matter, giving the universe its web-like structure.
While Tully agreed that the BOSS Great Wall is indeed the biggest structure in the universe we’ve found so far, he doesn’t think it will change our theories of how the cosmos gets its shape. (There is another contender for largest structure in the universe, but instead of being made of something, it’s made of nothing.)
“It is not surprising that if we look at a bigger patch of the universe we find something bigger,” Tully said. “But not so much bigger that it disrupts the generally held view of structure formation.”
What’s more, Tully said that the BOSS Great Wall won’t be the last word on giant superstructures—there’s plenty of universe left to explore. “Look in a new place and you’ll find something new,” Tully said.
Astronomers already know where to look next. Lietzen explained that the survey data the team used to figure out the large-scale structure of objects only covered a quarter of the night sky. “There could very well be another equally big system of superclusters somewhere in the Southern sky, for example,” Lietzen said.
*Sloan refers to the Sloan Digital Sky Survey, SDSS, using the SDSS telescope at Apache Point, NM, USA
**Baryon Oscillation Spectroscopic Survey also ran on the SDSS telescope.
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