Indian astronomers make history, discover supercluster Saraswati 

Namrata Devikar
Thursday, 13 July 2017

Four scientists from Pune are part of team that discovered galaxies' supercluster 

Pune: A team of astronomers from city-based Inter University Centre for Astronomy and Astrophysics (IUCAA) and Indian Institute of Science Education and Research (IISER), along with members of two other Indian universities, have identified a previously unknown and extremely large supercluster of galaxies located in the direction of the constellation Pisces. The supercluster has been named Saraswati. 

This is one of the largest known structures in the nearby universe and is at a distance of 4,000 million (400 crore) light-years away from us. 

Explaining the importance of the discovery, Shishir Sankhyayan, one of the members on the project from IISER, said that superclusters are the largest coherent structures in the cosmic web. 

It is also an important discovery, as it is the first discovery of a supercluster to have been made from Indian soil, he said. 

“A supercluster is a chain of galaxies and galaxy clusters, bound by gravity, often stretching to several hundred times the size of clusters of galaxies, consisting of tens of thousands of galaxies," Sankhyayan said. 

Important achievement 
This newly-discovered ‘Saraswati’ supercluster extends over a scale of 600 million light-years and may contain the mass equivalent of over 20 million billion suns,” said Sankhyayan. 

He added that when astronomers look far away, they see the universe from long ago, since light takes a while to reach us. “The Saraswati supercluster is observed as it was when the universe was 10 billion years old. Hence, this is a major breakthrough," said Sankhyayan. 

The discovery of these extremely large structures force astronomers into re-thinking the popular theories of how the universe got its current form, starting from a more-or-less uniform distribution of energy after the Big Bang. 

In recent years, the discovery of the present-day universe being dominated by 'Dark Energy', which behaves very differently from gravitation, might play a role in the formation of these structures, suspect astronomers. 

Surprise discovery 
Joydeep Bagchi from IUCAA, the lead author of the paper and co-author Sankhyayan, said they were very surprised to spot this giant wall-like supercluster of galaxies, visible in a large spectroscopic survey of distant galaxies, known as the Sloan Digital Sky Survey. This instrument is based in Mexico. 

“This supercluster is clearly embedded in a large network of cosmic filaments traced by clusters and large voids. Previously, only a few comparatively large superclusters have been reported, like the ‘Shapley Concentration’ or the ‘Sloan Great Wall’ in the nearby universe, while the ‘Saraswati’ supercluster is a far more distant one,” said the astronomers. 

They said their work will help to shed light on the perplexing question of how such extreme large scale, prominent matter-density enhancements had formed billions of years in the past when the mysterious Dark Energy had just started to dominate structure formation. 

THE SCIENTISTS 
From IUCAA: Somak Raychaudhury (Director), Joydeep Bagchi (Astronomer), Pratik Dabhade (Research Fellow). 
From IISER: Shishir Sankhyayan (PhD student) 
From Newman College, Thodupuzha, Kerala: Joe Jacob (Department of Physics) 
From NIT Jamshedpur: Prakash Sarkar (Department of Physics) 

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