29 November 2012
An international team led by academics from the University of Central Lancashire (UCLan) has found the largest known structure in the universe – a large quasar group that challenges scientific understanding of our universe.
Quasars are galaxies from the early days of the universe that undergo brief periods of extremely high brightness that make them visible across huge distances. These periods are ‘brief’ in astrophysics terms but actually last 10-100 million years.
Since 1982 it has been know that quasars tend to group together in clumps or ‘structures’ of surprisingly large sizes, forming large quasar groups or LQGs.
“It challenges the Cosmological Principle, which has been widely accepted since Einstein”
The team, led by Dr Roger Clowes from UCLan’s Jeremiah Horrocks Institute, includes Kathryn Harris from UCLan, Srinivasan Raghunathan and Luis E. Campusano from Universidad de Chile, Ilona K. Sochting from the University of Oxford and Matthew J. Graham from the California Institute of Technology. Together they have identified the LQG which is so significant in size it challenges the Cosmological Principle.
The Cosmological Principle is 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’.
“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”
To give some sense of scale, our galaxy, the Milky Way, is separated from its nearest neighbour, the Andromeda Galaxy, by about 0.75 Megaparsecs (Mpc) or 2.5 million light-years.
Whole clusters of galaxies can be 2-3 Mpc across but LQGs can be 200 Mpc or more across. Although, based on the Cosmological Principle and the modern theory of cosmology, calculations suggest that astrophysicists should not be able to find a structure larger than 370 Mpc.
However, Dr Clowes’ discovery has a typical dimension of 500 Mpc. But because it is elongated, its longest dimension is 1,240 Mpc or 4 billion light years - that is some 1,650 times larger than the distance from the Milky Way to Andromeda.
Dr Clowes said: “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.
“More importantly, 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.”