A multinational team of astronomers led by the University of Central Lancashire has detected a large group of quasars that may be the largest known structure in the Universe.

This image shows the Huge-LQG in the constellation Leo, white crosses mark the positions of quasars (Roger G. Clowes et al / Centre de Données astronomiques de Strasbourg / SIMBAD)

Quasars are the nuclei of galaxies from the early days of the Universe that undergo brief periods of extremely high brightness that make them visible across huge distances. Astronomers know that quasars tend to group together in clumps of surprisingly large sizes, forming large quasar groups (LQGs).

The newly discovered structure, named the Huge-LQG, is a group of 73 quasars located in the constellation Leo. It is so large that it would take a vehicle traveling at the speed of light some 4 billion years to cross it.

According to the astronomers, the discovery also challenges the Cosmological Principle – the assumption that the Universe, when viewed at a sufficiently large scale, looks the same no matter where you are observing it from.

The modern theory of cosmology is based on the work of Albert Einstein, and depends on the assumption of the Cosmological Principle. The Principle is assumed but has never been demonstrated observationally beyond reasonable doubt.

To give some sense of scale, whole clusters of galaxies can be 2-3 Megaparsecs across, but LQGs can be 200 Megaparsecs or more across. Based on the Cosmological Principle and the modern theory of cosmology, calculations suggest that scientists should not be able to find a structure larger than 370 Megaparsecs.

The Huge-LQG however has a typical dimension of 500 Megaparsecs. But because it is elongated, its longest dimension is 1200 Megaparsecs – some 1600 times larger than the distance from the Milky Way to Andromeda.

“While it is difficult to fathom the scale of this LQG, we can say quite definitely it is the largest structure ever seen in the entire Universe. This is hugely exciting – not least because it runs counter to our current understanding of the scale of the Universe,” said Dr Roger Clowes of the University of Central Lancashire Jeremiah Horrocks Institute, lead author of the study accepted for publication in theMonthly Notices of the Royal Astronomical Society (arXiv.org version).

“Even travelling at the speed of light, it would take 4 billion light years to cross. This is significant not just because of its size but also because it challenges the Cosmological Principle, which has been widely accepted since Einstein. Our team has been looking at similar cases which add further weight to this challenge and we will be continuing to investigate these fascinating phenomena.”

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Bibliographic information: Roger G. Clowes et al. 2013. A structure in the early universe at z ∼ 1.3 that exceeds the homogeneity scale of the R-W concordance cosmology.Mon. Not. R. Astron. Soc., accepted for publication; arXiv:1211.6256

• Astronomy