Sunday, July 16, 2017

Indian Astronomers Discover New Giant Supercluster

The distribution of galaxies, from Sloan Digital Sky Survey (SDSS), in Saraswati supercluster. It is clearly visible that the density of galaxies is very high in the Saraswati supercluster region. The typical size of a galaxy here is around 250,000 light years. The galaxy sizes are increased for representation. Credit: Inter University Centre for Astronomy & Astrophysics (IUCAA)

A team of astronomers from India has detected a new extremely massive and large supercluster spanning at least 650 million light years across. The newly found group of galaxies and galaxy clusters was named Saraswati – after the ancient Indian goddess of knowledge, music, art, wisdom, and nature. The finding was presented in a paper published July 10 on arXiv.org.

Superclusters are among the largest-known structures of the Universe. These giant associations, heavily packed with galaxies, are hundreds of millions of light years in diameter. Astronomers estimate that there are about 10 million superclusters in the observable universe.

Recently, a group of researchers led by Joydeep Bagchi of the Inter-University Centre for Astronomy and Astrophysics in Pune, India, has found a new enormous concentration of galaxies, which turns out to be one of the largest and most massive superclusters known to date. The detection was made as part of the Sloan Digital Sky Survey (SDSS), which provides detailed three-dimensional maps of the Universe.

“We report the discovery of an extremely massive and large supercluster (called Saraswati) found in the Stripe 82 region of SDSS. This supercluster is a major concentration of galaxies and galaxy clusters, forming a wall-like structure spanning at least 200 Mpc across at the redshift z ≈ 0.3,” the researchers wrote in the paper.

Stripe 82 is currently the largest three-dimensional spectroscopic sample of galaxies with a high sampling density. Bagchi’s team has analyzed the data from the multi-fiber spectrograph mounted on the Sloan 2.5 m telescope at Apache Point Observatory in New Mexico, which observed the central part of the Stripe 82 region.

Saraswati was noticed while exploring the large-scale distribution of galaxies surrounding an unusual filamentary, merging galaxy cluster designated ZwCl 2341.1+0000. The researchers identified the new supercluster as a high density region of galaxies at mean redshift of about 0.28.

With a length of approximately 650 million light years, Saraswati has a wall-like morphology. The main body of this supercluster contains at least 43 massive galaxy clusters with a total mass of about 20 quadrillion solar masses. The researchers also found that the central region of Saraswati with a radius of 65 million light years and mass at least four quadrillion solar masses may be collapsing.

What is also noteworthy, the newly detected supercluster is surrounded by a network of galaxy filaments, clusters, and large voids about 130 to 550 million light years in diameter. Such voids could offer important hints about the formation of Saraswati.

“A possible clue to the formation of this large galactic superstructure is provided by the detection of huge voids of ~ 40−170 Mpc diameter observed around the main wall-like overdense structure of Saraswati. In ΛCDM cosmology, space within voids expands faster than the background Hubble expansion and thus matter inside voids will have an outward component of peculiar velocity away from the void centers. Hence, matter within voids will be swept up into dense sheets or pancakes, which intersect one another, forming long galaxy filaments of the cosmic web separating neighboring voids,” the paper reads.

The authors of the paper concluded that Saraswati and its surroundings should be surveyed in greater depth with more galaxy redshifts taken on a wider scale. Such studies could improve our understanding of physical processes involved in the growth of enormous cosmic structures in the distant universe.

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