Billion-light-year galactic wall may be largest object in cosmos
Astronomers peering into the distant universe have discovered the BOSS Great Wall, a vast superstructure of 830 galaxies that is a billion light years across
DAILY NEWS 8 March 2016
By Joshua Sokol
Here’s the latest reminder that space is really, really big. At a cool billion light years across, a distant complex of galaxy superclusters may be the largest structure yet found in the cosmos.
Individual galaxies like our own Milky Way are bound together by gravity into clusters, and these clusters clump into superclusters. These can in turn link together into long lines of galaxies called walls. On the grandest scales, the universe resembles a cosmic web of matter surrounding empty voids – and these walls are the thickest threads.
In the nearby universe, we know of the Sloan Great Wall, and in 2014, the Milky Way was found to be part of a supercluster system called Laniakea. Both are enormous. But the newly spotted BOSS Great Wall, with a total mass perhaps 10,000 times as great as the Milky Way, is two-thirds bigger again than either of them.
Heidi Lietzen of the Canary Islands Institute of Astrophysics and her team found it by looking for clumped-together galaxies in a vast area between 4.5 and 6.4 billion light years away. In all that space, one dense, giant system stood out.
“It was so much bigger than anything else in this volume,” Lietzen says. The BOSS Great Wall contains 830 galaxies we can see and probably many more that are too far away and faint to be observed by survey telescopes.
Like other galaxy walls, this one’s size is a little subjective.
“I don’t entirely understand why they are connecting all of these features together to call them a single structure,” says Allison Coil of the University of California in San Diego. “There are clearly kinks and bends in this structure that don’t exist, for example, in the Sloan Great Wall.”
Brent Tully of the University of Hawaii, who discovered the Laniakea cluster, says that deciding what constitutes a single structure depends on your definition.
A denser region of galaxies is traditional, he says, and indeed the new wall contains five times as many galaxies as an average patch of sky. But tracking whether the galaxies are moving together – impossible, given how far away they are – might give a different answer.
Galaxy superclusters also have competition for the “biggest known object” crown. Some distant light sources likequasars or gamma ray bursts seem to be clustered together in certain regions of the sky. If they are truly connected, they belong to structures so large that current cosmological theories can’t explain them.
But many astronomers aren’t sure that these objects really belong together, as they lack a physical mechanism to link them. Instead, they prefer to look for huge linkages of galaxies that sit on the cosmic web. In that arena, the new-found BOSS Great Wall is king.
Journal reference: arxiv.org/abs/1602.08498, to appear in Astronomy & Astrophysics
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