Astronomers at the University of Central Lancashire (UCLan) say they have discovered the largest known structure in the universe, a clump of active galactic cores that stretches an astounding 4 billion light-years.
According to the team of scientists led by Dr Roger Clowes from UCLan's Jeremiah Horrocks Institute, the large quasar group (LQG) is so large that it would take a vehicle travelling at the speed of light 4 billion years to cross it.
The teams published their results on January 11, in the journal Monthly Notices of the Royal Astronomical Society.
The structure, a large quasar group (LQG), is a collection of extremely luminous galactic nuclei powered by supermassive central black holes. According to the astronomers, the new LQG is so large that it raises new questions about long accepted cosmological theories.
Lead author Roger Clowes, of the University of Central Lancashire in England, 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.
R. G. Clowes / UCLan
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
"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."
Quasars, the brightest bodies in the universe, have been known since 1982 to tend to assemble in large groups and form unusually large structures, some of which are known to span in excess of 600 million light-years across. They are nuclei of galaxies formed at an early stage in the evolution of the universe. They are extremely bright over a "brief period" (10-100 million years) of the evolution of the galaxy such that they are visible across great distances.
The new quasar group discovered by the UCLan researchers, however, smashes all previous records. The data for the new group, gathered by the Sloan Digital Sky Survey, found that it is composed of 73 quasars and spans about 1.6 billion light years in most directions, though it is 4 billion light-years across at the widest observed point.
The researchers explain that to put the sheer immensity of this structure in perspective, the disc of our Milky Way galaxy is about 100,000 light-years wide and the Milky Way is separated from its nearest galactic neighbor, Andromeda, by about 2.5 million light-years. The researchers write:
"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. [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."
According to the team, the LQG is so massive that theory predicts that it should not exist because it appears to violate the long accepted assumptions of the Cosmological Principle, which holds "that the universe is essentially homogeneous when viewed at a sufficiently large scale, in other words, "it looks the same no matter where you are observing it from."
The researchers' observation is significant because current cosmological theories are based on the Cosmological Principle that stems from the work of Albert Einstein. Although the principle is widely assumed to be true, it has never been demonstrated or proved directly by observations of the large scale structure of the universe.
Astrophysicists say calculations suggest that structures larger than about 1.2 billion light-years should not exist.
Clowes said: "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."