Indian astronomers discover 34 giant alien radio sources

The Giant Metrewave Radio Telescope at the National Centre for Radio Astrophysics is located near Pune (Image:TIFR)

A team of Indian radio astronomers has identified 34 new giant radio sources (GRSs) using the Giant Metrewave Radio Telescope (GMRT) operated by the Tata Institute of Fundamental Research (TIFR). This discovery, derived from the TIFR GMRT Sky Survey Alternative Data Release 1 (TGSS ADR1) at 150 MHz, includes some of the most distant GRSs known. Notably, two of these sources challenge long-held beliefs about the environments in which GRSs form.

GMRT's Role in Astronomy
The GMRT, located near Khodad village, about 90 km north of Pune, is a state-of-the-art facility operated by the National Centre for Radio Astrophysics (NCRA) of TIFR. From 2010 to 2012, the GMRT conducted the TIFR GMRT Sky Survey (TGSS) to map the radio sky at 150 MHz, covering approximately 90% of the sky. This survey has proven to be a treasure trove for astronomers, enabling significant discoveries like these 34 new GRSs.

Unveiling Cosmic Giants
GRSs are among the universe's largest structures, spanning millions of light-years and puzzling astronomers with their enormous size and rarity. The team behind this discovery includes PhD students Netai Bhukta (SKBU, India) and Souvik Manik (MCC, India), alongside astronomers Sabyasachi Pal (MCC, India) and Sushanta K Mondal (SKBU, India). The team leveraged the TGSS for its low frequencies and the sensitivity of the GMRT to identify these colossal structures.

The Nature of GRSs
According to Sabyasachi Pal, GRSs are some of the universe’s most colossal structures, stretching across millions of light-years, equivalent to lining up several tens of Milky Way galaxies in a row. At their core lies a supermassive black hole, with masses ranging from ten million to one billion times that of the Sun. This black hole serves as the engine, pulling in surrounding matter that becomes ionised and generates powerful electromagnetic forces. These forces propel material outward, forming jets of hot plasma that create massive lobes of radio emissions extending far beyond the visible galaxy.

Challenges in Detection
Detecting GRSs is challenging due to their immense size and the faint "bridge emission" connecting their lobes, often invisible in high-frequency surveys. Low-frequency surveys like the TGSS are better suited for identifying these sources. Netai Bhukta said that the vast projected lengths of GRSs make them key candidates for studying the evolution of radio sources and the intergalactic medium.

Challenging Prevailing Theories
The discovery of two GRSs, J0843+0513 and J1138+4540, questions the common understanding that GRSs grow in low-density environments. Souvik Manik emphasised that the environment alone does not dictate the exceptional size of GRSs.

As researchers plan to present new GRS samples in forthcoming articles, they aim to conduct detailed analyses based on multiwavelength observations. These studies will shed more light on the formation and growth of giant radio sources, enhancing our broader understanding of the universe.