An international team of astronomers, led by academics from the University of Central Lancashire (UCLan), has found the largest known structure in the universe. The large quasar group (LQG) is so large that it would take a vehicle travelling at the speed of light some 4 billion years to cross it. The team publish their results in the journal Monthly Notices of the Royal Astronomical Society.
The coloured background indicates the peaks and troughs in the occurrence of quasars at the distance of the LQG. Darker colours indicate more quasars, lighter colours indicate fewer quasars. The LQG is clearly seen as a long chain of peaks indicated by black circles. (The red crosses mark the positions of quasars in a different and smaller LQG). The horizontal and vertical axes represent right ascension and declination, the celestial equivalent of longitude and latitude. The map covers around 29.4 by 24 degrees on the sky, indicating the huge scale of the newly discovered structure. Credit: R. G. Clowes / UCLanQuasars 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. These periods are 'brief' in astrophysics terms but actually last 10-100 million years.
Since 1982 it has been known that quasars tend to group together in clumps or 'structures' of surprisingly large sizes, forming large quasar groups or LQGs.
The team, led by Dr Roger Clowes from UCLan's Jeremiah Horrocks Institute, has identified the LQG which is so significant in size it 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, 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. 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.
Dr Clowes' 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.
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. This is hugely exciting – not least because it runs counter to our current understanding of the scale of the universe.
"Even travelling 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."
Dr Roger G. Clowes
Reader in Astrophysics
University of Central Lancashire
Tel: +44 (0)1772 893 526
Dr Robert Massey
Royal Astronomical Society
Tel: +44 (0)20 7734 3307 x214
Mob: +44 (0)794 124 8035
Images and captions
An artist's impression of a quasar (with caption and image credit) is available from the European Southern Observatory http://www.eso.org/public/images/eso1122a/
A map of the distribution of quasars that make up the newly discovered LQG can be downloaded from http://www2.uclan.ac.uk/adv/skydist_Huge-LQG_CCLQG.jpg
Caption: The coloured background indicates the peaks and troughs in the occurrence of quasars at the distance of the LQG. Darker colours indicate more quasars, lighter colours indicate fewer quasars. The LQG is clearly seen as a long chain of peaks indicated by black circles. (The red crosses mark the positions of quasars in a different and smaller LQG). The horizontal and vertical axes represent right ascension and declination, the celestial equivalent of longitude and latitude. The map covers around 29.4 by 24 degrees on the sky, indicating the huge scale of the newly discovered structure. Credit: R. G. Clowes / UCLan
Dr Clowes worked with Kathryn Harris (UCLan), Srinivasan Raghunathan, Luis E. Campusano (Universidad de Chile), Ilona K. Sochting (University of Oxford) and Matthew J. Graham (California Institute of Technology).
The team's paper will be published online in the Oxford University Press journal Monthly Notices of the Royal Astronomical Society at 9am on Friday 11 January. After the embargo expires the paper will be available via http://mnras.oxfordjournals.org/content/early/2013/01/07/mnras.sts497.full. A preprint of the paper can be seen at http://arxiv.org/abs/1211.6256
Notes for editors
The University of Central Lancashire (UCLan) has developed an enviable reputation as an institution that innovates, evolving its course portfolio to over 500 undergraduate programmes and 180 postgraduate courses. The University has an established research reputation within the areas of Business, Health, Humanities and Science. In the recent Research Assessment Exercise, all 17 subject areas submitted were rated as containing research of international excellence while 11 areas were assessed to be undertaking research which is world-leading. With approximately 35,000 students, the University indirectly contributes close to £250 million into the regional economy every year. UCLan is currently in the process of spending more than £120 million on new buildings and facilities to support teaching, learning and leisure activities.
The Royal Astronomical Society (RAS, www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3500 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.