An Indian radio astronomers-led team announced the discovery of 34 new giant radio sources using data from TIFR GMRT Sky Survey Alternative Data Release 1 at 150 MHz.
Many of these GRSs are among the best known, with two of them pushing against the previously accepted theories regarding their environments.
The sheer size and rarity of GRSs continue to puzzle astronomers, who would like to know what makes them grow into such enormous structures.
The discovery used a crucial contribution from the Giant Metrewave Radio Telescope, located near Khodad village, about 90 km north of Pune in India.
Photo Credit: Some of the Giant Radio Sources exhibiting complex structures and morphology.
The GMRT, constructed and operated by the NCRA of the TIFR, covered the radio sky at 150 MHz using the GMRT during the period from 2010 to 2012, covering about 90% of the sky. It was the survey data from TGSS that was important for the findings of the researchers.
The discovery was made by a team consisting of two Ph.D. students: Netai Bhukta from SKBU, India, and Souvik Manik from MCC, India; astronomers Sabyasachi Pal from MCC, India; and Sushanta K.
Mondal from SKBU, India. Their study harnessed TGSS data with low frequencies and the sensitivity of GMRT, thereby making it feasible to identify 34 GRSs.
Giant radio sources are likely to be the largest single structures in the universe, with end-to-end extents of millions of light years. They are driven by supermassive black holes with masses ten million to a billion times that of the Sun, residing at the centre of the host galaxy.
These black holes ionise surrounding matter, developing powerful electromagnetic forces that propel material to the edges, forming jets of hot plasma and huge lobes of radio emission.
It is believed that GRSs are the very last stage in the evolution of radio galaxies. Their enormous size makes them interesting for studying the evolution of radio sources and the intergalactic medium. Nevertheless, their detection is difficult due to the bridge emission, which often remains invisible among the two lobes. Low-frequency radio surveys, like TGSS, are more appropriate for searching for these structures than high-frequency ones.
Two of the newly discovered GRSs, J0843+0513 and J1138+4540, challenge the notion that GRSs grow only in low-density environments. The authors themselves acknowledge that environmental factors are not solely responsible for dictating the size of GRGs. It has been proposed to include new samples and detailed physical properties in forthcoming articles based on multi-wavelength observations.
It is one of the important discoveries published in the Astrophysical Journal Supplement Series of the American Astronomical Society.
