Scientists are wondering whether things are getting too hot for one of the most venerable assumptions of cosmology, propounded by none other than Albert Einstein himself.
The discovery of the Huge Large Quasar Group (LQG) was announced by a multinational team of astronomers led by Dr Roger G. Clowes of the University of Central Lancashire. Other members of the team included 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 Huge-LQG is 4 billion light years in length, that is, light would take 4 billion years to cross it end to end. That's nearly one-twentieth the estimated diameter of the whole known Universe. The team used data from the Sloan Digital Sky Survey, the most comprehensive 3D map of the universe. They identified 73 quasars, the glowing cores found at the centre of galaxies, surrounding the central black holes.
The reason this discovery has sent ripples across the cosmologists world is that it appears to be going against the Cosmological Principle, which says that "the universe, when viewed at a sufficiently large scale, looks the same no matter where you are observing it from" according to the Royal Astronomical Society, London. Einstein had made this assumption in order to make his theory of general relativity work for the whole Universe.
Till the discovery of the Huge-LGQ, it was assumed that the upper limit of size for cosmic structures was somewhere around one billion light years. Another cluster of quasars, discovered by Clowes himself in 1982 was estimated to be of that size. The Huge-LQG is four times as large, and hence shakes up the science of the Universe considerably.
How do we know that the 73 quasars are part of a connected "structure"? Responding to this query posed by TOI, Dr.Clowes said, "With the quasars we look for a set that connects within a specified distance from one quasar to the next. We then assess the statistical significance by calculating the volume that encloses them and testing whether the resulting density is a significant departure from uniformity. Essentially, it's a connection algorithm combined with statistical significance. An analogy might be of looking for an island emerging from an ocean".
The record for the largest structure in the Universe was previously held by the Sloan Great Wall, a 1.38 billion light years long filament or wall of galaxies. However, many scientists have felt that the Sloan Great Wall is simply three clusters of galaxies which appear to be aligned.
"I believe that in the case of the SGW it was simply a visual judgement from the maps of the galaxy distribution," Clowes too explains.
However, he adds that one or two papers have been published that "have applied retrospectively connection algorithms similar to ours" to the Sloan Great Wall
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