An international team of astronomers has discovered the largest known structure in the universe which is about 4 billion light-years in dimension across, compared to 120,000 light years for 'Milky Way,' the galaxy to which our earth belongs to. The large quasar group is so large it would take a spacecraft travelling at the speed of light some 4 billion years to cross it. The team led by Dr Roger Clowes of Britain's University of Central Lancashire, has found a large quasar group (LQG), which is so large that it would take a spaceship travelling at the speed of light some 4 billion years to cross it, the Royal Astronomical Society said in a release. The report on the findings is published in the journal Monthly Notices of the Royal Astronomical Society. The LQGs 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 billions of light-years away. The 'brief' in astrophysics mean 10-100 million years. The discovered structure is so large that it challenges Albert Einstein's cosmological principle, which assumes that the universe, when viewed at a sufficiently large scale, looks the same irrespective of wherever you are observing it from. "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,'' Clowes said. ''This is hugely exciting – not least because it runs counter to our current understanding of the scale of the universe,'' he continued. This newly identified LQG has a typical dimension of 1.6 billion light-years or 500 megaparsecs, each megaparsec equaling 3.3 million light-years. But because it is elongated, its longest dimension is some 4 billion light-years. For comparison, the distance from our Milky Way galaxy to its nearest neighbour, the Andromeda galaxy, is about 2.5 million light-years only, or some 1,600 times smaller. According to calculations based on the cosmological principle and modern theories, astrophysicists should
not be able to find a galaxy larger than 1.2 billion light years. The newly discovered structure is about 3.5 times larger than the theoretical limit. ''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," Clowes said. Astronomers discovered their first large cluster of quasars in 1982 and two more by 1991. With the advent of Sloan digital sky survey, using a dedicated 2.5-metre wide angle optical telescope, more quasar clusters have been found including the latest. Some other researchers at the Harvard-Smithsonian Centre for Astrophysics in Cambridge acknowledge that the finding brings to light a key question in modern cosmology regarding the size scale at which the uneven distribution of matter gives way to a uniform average across the universe. However, they consider the new evidence isn't strong enough to challenge the notion of the cosmological principle of large-scale uniformity. It could also represent the hint of a new, improved threshold larger than 1.2 billion light-years. Moreover, it is unclear whether the discovered cluster is truly single in structure. For instance, what looks like one huge cluster may actually be two structures that look as though they are one because of the viewing angle from Earth, they say. If further observations reveal it as a distinctly rare structure, it could indicate that the cosmos might not be so uniform as thought, and could trigger new theories about the evolution of the universe. Source: Domain-B
