If you thought the cosmic web was intricate enough, think again. A team of astrophysicists recently used gamma-ray bursts – those spectacular, mysterious explosions of energy from the farthest reaches of space – to discover that the largest known structure in the universe may be even larger than previously thought.
This structure is the Great Wall of Hercules-Corona Borealis, a string of groups and clusters of galaxies stretching about 10 billion light-years across. The new estimate of the structure’s size is causing a new headache for standard cosmological models, as it appears to be even larger than the previous high estimate of about 9.8 billion light-years.
In the new study, which has not yet been peer-reviewed and is posted on the arXiv preprint server, a joint Hungarian-American research team led by István Horváth of the Budapest University of Public Service scanned the sky for patterns. The team used a dataset of 542 gamma-ray bursts with known redshifts, which essentially means that the distance to them is known. The bursts are essentially natural flares – extremely bright bursts of high-energy light that can eclipse entire galaxies for brief moments. These bright flashes can be observed from great distances, making them ideal cosmic guideposts. And when astronomers begin to notice that they are clustered in one area of the sky, serious questions begin to arise.
The researchers checked the distribution of the points in the universe and found that the Great Wall – first discovered in 2014 – can span a redshift range from z = 0.33 to z = 2.43. In other words: The structure stretches over an incredible amount of space and time. We are talking about billions of light years. And no, it’s not a pixel glitch or some strange telescope fluke – the authors have ruled out statistical artifacts and sampling bias.
But according to the cosmological principle, the Universe should be approximately homogeneous on a large scale. The generally accepted upper limit for such structures is about 370 megaparsecs (about 1.2 billion light-years), the article says. But the Great Wall of Hercules-Corona Borealis – named after the constellations in the same region – is well outside that range. It makes Sloan’s Big Dipper and even the Giant Quasar Group look like dollhouses.
The Hercules-Coronae Superstructure of the Aurora Borealis is not just a patch of sky cluttered with gamma-ray bursts – it is most likely a dense region of galaxies, stars, and dark matter held together by gravity. In addition, bright gamma-ray bursts can reveal structures invisible to other studies; because these bursts are associated with massive star deaths, they can trace the process of star formation in a way that galaxy studies cannot.
If the team of authors of the new study is right-that structures of this enormous size can form in the Universe-then the cosmological principle may need to be adjusted. Of course, it is also possible that we are missing something fundamental in our understanding of how the universe has evolved. Frankly, it’s probably both.
So the next time you look up at the stars and wonder how small you feel, just remember that you are even smaller – at least compared to the “wall” that almost makes the scale of the cosmos seem mundane.
