An Indian-led international team of astronomers has discovered an enigmatic object in the sky using the Giant Meter Wave Radio Telescope (GMRT). The GMRT, the largest in the world and the most powerful radio telescope in the low frequency range of 150-1,500 MHz of the National Centre for Radio Astrophysics of Tata Institute of Fundamental Research (NCRA-TIFR), has been widely used by astronomers from all over the world.

Observing at low radio frequencies with the GMRT is like making a deeper archaeological excavation to unravel the past history of jet activity of the black holes. Multiple evolutionary processes, driving evolution of galaxies and clusters of galaxies have been discovered by the team using the GMRT.

Dr Ananda Hota of Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), Taiwan, discovered the exotic galaxy having a combination of properties never seen before and dubbed it SPECA (Spiral-host Episodic Radio Galaxy Tracing Cluster Accretion). The SPECA is only the second spiral as opposed to elliptical galaxy known to produce large, powerful jets of subatomic particles moving at nearly the speed of light.  This is probably the most exotic galaxy with a black hole and has the potential to teach new lessons about how galaxies and clusters of galaxies formed in the early universe.

It also is one of only two galaxies to show that such activity occurred in three separate episodes. The reason behind this on-off activity of the black hole to produce jets is unknown.

“The on-going TIFR GMRT Sky Survey (TGSS) is going to discover more SPECA-like galaxies and Dr Hota’s discovery is a potential  demonstrator,” said Dr Sandeep Sirothia of NCRA-TIFR.

“This kind of reborn radio galaxies are the laboratories to understand many puzzling aspects of black holes,’’ said Dr Chiranjib Konar of ASIAA.

The SPECA is a `missing link’, rare in the nearby universe, but is anticipated to be common in the early universe when black holes, galaxies and clusters were very young in their formative era, informed Dr Hota.

This is probably the first evidence of the process of growth and regulation of clusters of galaxies by supersonic in fall of matter from the cosmic-web and black holes to control that by outflow of powerful jets.

“It is an outstanding discovery that is very important for cluster formation models and highlights the importance of sensitive observations at meter wavelengths provided by the GMRT,” said Padmashri awardee Prof Govind Swarup, FRS, who is considered the ‘father’ of Indian radio astronomy and the chief architect of the GMRT.

In addition to Dr Hota, Dr Sirothia and Dr Konar, the research team includes Dr Youichi Ohyama, and Dr Satoki Matsuchita of ASIAA,  Suk Kim and Professor Soo-Chang Rey of Chungnam National University in Korea, Professor DJ Saikia of NCRA and Dr Judith H Croston of the University of Southampton in England.