An international group of astronomers says they've detected what may be the biggest feature or structure in the known universe, a circular ring of nine galaxies that stretches five billion light years across.
The galaxies have been detected by gamma ray bursts, the brightest events in the universe, created when massive stars in a galaxy collapse into black holes.
Astronomers have long used such bursts to locate and map the locations of their distant host galaxies, and such bursts are cataloged in the Gamma Ray Burst Online Index, a precise listing of burst distances and locations, creating a cosmic map.
Using a number of space-based and Earth-based observatories, U.S. and Hungarian scientists detected the ring's galaxies — all at roughly the same distance from earth, about seven billion light years away — using gamma ray bursts.
The galaxies are in a circle that takes up 36 degrees of the sky — 70 times the diameter of the moon when it's full — which suggests the ring is at least five billion light years from one side to the other.
They are considered an associated structure, as there is only a one in 20,000 probability of the gammy ray bursts being in a circular distribution by chance, says Lajos Balazs of the Konkoly Observatory in Budapest, leader of a study appearing in the Monthly Notices of the Royal Astronomical Society.
Scientists had previously thought there was a theoretical limit to how big a cosmological structure could be — they put the limit at around 1.2 billion light years — but the newly-discovered ring appears nearly five times as big.
If the cosmic ring is an actual spatial structure, the researchers say, we must be seeing it almost face-on because of the almost negligible differences in the distances of the gamma ray bursts from the ring's center.
Alternatively, the object might be the projection of a sphere, they suggest, where the bursts all happened in a 250-million-year period, a brief timescale when compared with the age of the universe.
Further study could establish if the ring is the result of known processes for galaxy formation or if theories of the evolution of the universe need a possible radical revision, the researchers say.
"If we are right, this structure contradicts the current models of the universe," says Balazs. "It was a huge surprise to find something this big — and we still don't quite understand how it came to exist at all."
