On January 11, 2013, the discovery of a vast grouping of 73s quasars, a form of supermassive black hole active galactic nuclei, with a minimum diameter of 1.4 billion light-years, stretched over four billion light-years at its widest point was announced by the University of Central Lancashire, as the largest known structure in the universe LQGs are thought to be precursors to the sheets, walls and filaments of galaxies found in the relatively nearby universe. The existence of structures of the magnitude of large quasar clusters was believed theoretically impossible. Cosmological structures had been believed to have a size limit of approximately 1.2 billion light-years.
The LQG 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'.
This year, a team led by Damien Hutsemékers from the University of Liège in Belgium used the FORS instrument on the VLT to study 93 quasars that were known to form huge groupings spread over billions of light-years, seen at a time when the Universe was about one third of its current age. "The first odd thing we noticed was that some of the quasars' rotation axis were aligned with each other -- despite the fact that these quasars are separated by billions of light-years," said Hutsemékers.
"The alignments in the new data, on scales even bigger than current predictions from simulations, may be a hint that there is a missing ingredient in our current models of the cosmos," observed Dominique Sluse of the Argelander-Institut für Astronomie in Bonn, Germany and University of Liège.
The team then went further and looked to see if the rotation axes were linked, not just to each other, but also to the structure of the Universe on large scales at that time.
When astronomers look at the distribution of galaxies on scales of billions of light-years they find that they are not evenly distributed. They form a cosmic web of filaments and clumps around huge voids where galaxies are scarce. This intriguing and beautiful arrangement of material is known as large-scale structure.
The new VLT results indicate that the rotation axes of the quasars tend to be parallel to the large-scale structures in which they find themselves. So, if the quasars are in a long filament then the spins of the central black holes will point along the filament. The researchers estimate that the probability that these alignments are simply the result of chance is less than 1%.
"A correlation between the orientation of quasars and the structurethey belong to is an important prediction of numerical models of evolution of our Universe. Our data provide the first observational confirmation of this effect, on scales much larger that what had been observed to date for normal galaxies," adds Sluse.
The team could not see the rotation axes or the jets of the quasars directly. Instead they measured the polarisation of the light from each quasar and, for 19 of them, found a significantly polarised signal. The direction of this polarisation, combined with other information, could be used to deduce the angle of the accretion disc and hence the direction of the spin axis of the quasar.
Whole clusters of galaxies can be 2-3 Mpc across but LQGs can be 200 Mpc or more across. 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. The newly discovered LQG however has a typical dimension of 500 Mpc. But because it is elongated, its longest dimension is 1200 Mpc (or 4 billion light years) - 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," says Dr Clowes of University of Central Lancashire'sJeremiah Horrocks Institute. "This is hugely exciting – not least because it runs counter to our current understanding of the scale of the universe. Even traveling at the speed of light, it would take 4 billion 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."
The team published their results in the journal Monthly Notices of the Royal Astronomical Society.
This research was presented in a paper entitled "Alignment of quasar polarizations with large-scale structures", by D. Hutsemékers et al., to appear in the journal Astronomy & Astrophysics on 19 November 2014.
The ESO team is composed of D. Hutsemékers (Institut d'Astrophysique et de Géophysique, Université de Liège, Liège, Belgium), L. Braibant (Liège), V. Pelgrims (Liège) and D. Sluse (Argelander-Institut für Astronomie, Bonn, Germany; Liège).
The Daily Galaxy via ESO