Recent work suggests that the upper limit to the largest gatherings of galaxies is about 1.2 billion to 1.5 billion light-years across. The structure that the team reports is nearly four times this theoretical limit.
What could be the largest structure yet seen in the observable universe has emerged from data taken during a 12-year survey of the night sky.
The discovery is an apparent cluster of quasars some 4 billion light-years across. If it holds up to further scrutiny, it could challenge a long-held assumption that at the cosmos's largest scales, the physical processes at work and the distribution of matter and energy are the same, regardless of an observer's location.
That's the view of the team formally reporting the results Friday in the journal Monthly Notices of the Royal Astronomical Society.
Quasars are the hyperactive centers of large galaxies and are among the brightest, most energetic objects in the sky. Some recent theoretical work suggests that the upper limit to the largest gatherings of galaxies is about 1.2 billion to 1.5 billion light-years across. The structure that the team reports is nearly four times larger than this theoretical limit.
Other researchers caution that evidence in the new discovery isn't strong enough to challenge this notion of large-scale uniformity, dubbed the cosmological principle.
But, they add, the work does highlight a key question in modern cosmology: What is the size scale at which the wildly uneven distribution of matter seen at small cosmic scales gives way to a uniform average across the universe as a whole?
"We don't know that," says Margaret Geller, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., whose research focuses on how the universe and its cosmic-scale structures formed and evolved. "And this is an indication that we don't know that."