Indian astronomers discover supercluster of galaxies, name it ‘Saraswati’
In a significant discovery, a team of Indian astronomers have identified a previously unknown, extremely large supercluster of galaxies located in the direction of constellation Pisces.
The supercluster of 43 galaxies, which they named “Saraswati”, is one of the largest known structures in the nearby universe, and is 4 billion light years away from us and may contain the mass equivalent of over 20 million billion suns
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. The Saraswati supercluster, for instance, extends over a scale of 600 million light years.
The Milky Way, the galaxy we are in, is part of a supercluster called the Laniakea Supercluster, announced in 2014 by Brent Tully at the University of Hawaii and collaborators.
The Saraswati discovery was made by astronomers from India’s Inter University Centre for Astronomy and Astrophysics (IUCAA) and the Indian Institute of Science Education and Research (IISER), both in Pune, and members of two other Indian universities. IUCAA is an autonomous institution set up by the India to promote the nucleation and growth of active groups in astronomy and astrophysics at Indian universities.
“This novel discovery is being published in the latest issue of The Astrophysical Journal, the premier research journal of the American Astronomical Society,” said an official statement from IUCAA.
“The Saraswati supercluster is observed as it was when the universe was 10 billion years old,” IUCAA said in the statement. Thus, the findings could push researchers to rethink the popular theories of how the universe got its current form.
“The long-popular ‘cold dark matter’ model of the evolution of the universe predicts that small structures like galaxies form first, which congregate into larger structures. Most forms of this model do not predict the existence of large structures such as the Saraswati Supercluster within the current age of the universe. The discovery of these extremely large structures thus 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,” the statement said.
Interestingly, Somak Raychaudhury, currently director of IUCAA and a co-author of the paper, had also discovered the first massive supercluster of galaxies on this scale (the Shapley Concentration), during his PhD research at the University of Cambridge decades ago.
In his paper published in the journal Nature in 1989, Raychaudhury had named the supercluster after the American astronomer Harlow Shapley, in recognition of his pioneering survey of galaxies.
Joydeep Bagchi from IUCAA, the lead author of the paper, and co-author Shishir Sankhyayan (PhD scholar at IISER, Pune) said, ‘’We 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 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, for example the ‘Shapley Concentration’ or the ‘Sloan Great Wall’ in the nearby universe, while the ‘Saraswati’ supercluster is far more distant one. Our work will help to shed light on the perplexing question; 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 duo said in a statement.