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Dying, giant radio galaxy catches astronomers’ attention

According to experts, while radio galaxies with size less than a million light years are common, giant radio galaxies are rare at large cosmic distances.

Written by Mihika Basu | Mumbai |
Updated: November 8, 2015 5:25:43 am

NCRA, GMRT,  TIFR, rare galaxy, gigantic galaxy, radio galaxy, mumbai newsASTRONOMERS at the National Centre for Radio Astrophysics (NCRA-Pune), Tata Institute of Fundamental Research (TIFR), are excited about the discovery of an extremely rare galaxy of gigantic size.

The Giant Metrewave Radio Telescope (GMRT) is watching the galaxy, about nine billion light years from earth. The scientists termed it the “rarest of the rare find”.

The galaxy emits radio waves and has an end-to-end extent of four million light years, making it a giant radio galaxy.

“There are multiple reasons that make this galaxy so rare. It has a large extent when you see it in the radio band and there are only about 100 such galaxies in the universe. It was discovered at a very large distance from the earth and there are only about five or six distant, giant radio galaxies.

The galaxy is a phase when radio emission are dying away, which makes it quite unique,” said Dr Yogesh Wadadekar, scientist at NCRA.

The experts said while radio galaxies with size less than a million light years are common, giant radio galaxies are rare, even more so, at large cosmic distances, where only a handful has been discovered so far.

This galaxy, known by its scientific name ‘J021659-044920’, is the newest member of this ‘elite’ group.

Under special circumstances, the central black hole of the galaxy stops producing radio jets, and the bright radio lobes fade away within a few million years.
This galaxy was caught in this dying phase, where radio jet appears to have been switched off and radio lobes have started fading.

“Such dying radio objects are best studied using a low frequency radio telescope such as GMRT. The GMRT, the world’s largest radio telescope facility operating at low radio frequencies, is an array of 30 fully steerable, 45 metre diameter antennas, spread over a 30 km region around Khodad, near Narayangaon town of Pune district,” added Wadadekar.

The GMRT, built and operated by National Centre for Radio Astrophysics, has been in operation since 2002.

For their analysis, the team combined GMRT observations with previous observations made using multiple international ground and space-based telescope facilities – XMM-Newton Space Telescope in X-ray, the Japanese Subaru telescope in optical, UK’s Infrared Telescope in near-infrared, NASA’s Spitzer Space Telescope in mid-infrared and the Jansky Very Large Array (USA) in high frequency radio bands.

By using data from multiple telescopes, the team could carry out a comprehensive and detailed analysis of physical conditions around this distant galaxy. This project funded by the Indo-French Centre for Promotion of Advanced Research, involved Aritra Basu from the Max Planck Institute for Radio Astronomy, Germany, Veeresh Singh from the University of Kwazulu-Natal, South Africa, Alexandre Beelen from the Institute of Space Astrophysics, France, and C H Ishwara-Chandra and Sandeep Sirothia from NCRA.

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