The biggest thing in the universe — sounds pretty straightforward, right?
Well, not exactly. We all love a good cosmological superlative — the hottest, the brightest, the most massive — but studying space is rarely that simple. In many cases, the "mosts" of the universe bend our theoretical properties of physics in ways we don't understand.
A group of international scientists have recently discovered something that's vying for the title of biggest thing in the observable universe: a clustered ring of galaxies located about 7 billion light-years away. But the ring, detailed in the latest monthly notice of the Royal Astronomical Society, is so big that some cosmologists are saying it violates the basic theoretical principles governing the universe.
The proposed cluster isn't visible from Earth because it's so far away. It was revealed to cosmologists after they observed nine gamma-ray bursts, which are the result of super-massive stars collapsing into black holes.
The bursts offer brief clues about the location of other galaxies. In this case, the bursts are so close together and similar to one another that scientists think they must be a single feature. The team said there's a very low chance — one in 20,000 — that the arrangement appeared by random chance.
This discovery is the latest addition to a mix of galaxy clusters referred to as galaxy filaments — the great walls and massive threads that clothe the vast voids of space. These features are so inconceivably large that scientists don't know how they could possibly be formed.
If you were to travel from one end of the new cluster to the other at the speed of light, it would take more than 5.6 billion years. Lajos Balazs, contributor to the ring's discovery and a professor from the Konkoly Observatory in Budapest, said that if we could see the feature in the night sky, it would be 70 times bigger than the moon.
But the ring has stiff competition for the title of "biggest." A team of scientists found another enormous cluster back in 2013, a tapestry of galaxies estimated to be somewhere around 10 billion light years across.
"The ring is based on distinct observations, and the first cluster is based upon a humongous over-density of bursts," said Jon Hakkila, an astrophysics professor at the College of Charleston who contributed to the discoveries of both the giant ring and the great wall.
He thinks the great wall will end up taking the throne, but added there's still a lot of research to be done because the wall doesn't have a strong, distinct boundary.
Regardless, both of these features are problematic because they might contradict what is known as the Cosmological Principle.
To understand the principle, consider sand on a beach. If you look at small sections of the sand, there might be points that stick out, maybe a small pebble here or an abnormally large mound there. But when observed at a larger scale, the sand looks relatively uniform.
That's theoretically the same way that the space works. There's no special place in the universe — no center, no edge, no area where stars cluster more than another place. Each region is governed by the same physical laws of nature.
If you want a mind-blowing illustration of what that looks like, check out this 3-D map from the Sloan Digital Sky Survey:
The Cosmological Principle has been a bedrock concept for scientists studying stars over the past couple of centuries because, unlike many other fields of science, there isn't much opportunity for experimentation. There's only one sky and one set of stars to work with.
These massive galaxy filaments breaks the rules, though. They are way too big to obey physical laws of gravity, which have previously limited the size of cosmological features to, at most, 1.2 billion light years.
So do these massive discoveries put the basic tenants of cosmology in jeopardy? That's still up for debate.
In 2013, Robert Clowes of the University of Central Lancashire discovered what he said was a quasar group about 4 billion light-years across, the first feature that was too big to exist under physical law. But the feature, called the Huge Large Quasar Group, fell under intense scrutiny when researchers started to question the statistical validity of its existence. They argued that his group of galaxies was the result of randomness — not due to actual physical properties pulling them together.
"People say, 'Well did you find them there because you were looking for them?'" Hakilla said. "A lot of the cosmologists are hoping that this is just going to go away."
So far, Balazs said his team's discovery has received a somewhat icy response from their fellow cosmologists.
"The first reaction is that they don't believe it," Balazs said. "Some people believe that it's only some statistical something."
Balazs argued that the staggering size of the ring cluster may end up not contradicting the principles of science. Instead, he said it could unlock clues to the mystery of star formation, helping us with much broader questions about the evolution of the universe.
"There's always some wiggle room," Hakilla said. "Scientists always have to add some bells and whistles based on the observations. It's not like cosmology will be overthrown."