TAG: GS 3: SCIENCE AND TECHNOLOGY
THE CONTEXT: A team of Indian radio astronomers utilized data from the TIFR GMRT Sky Survey (TGSS) to identify 34 new giant radio sources.
EXPLANATION:
- This discovery, published in the Astrophysical Journal Supplement Series (ApJS) of the American Astronomical Society, marks a significant contribution to the field of radio astronomy.
Significance of the Discovery
- The discovery of these 34 GRSs is noteworthy for several reasons:
- Expansion of Known GRS Population:
- Historically, only about 100 GRSs were known 20 years ago.
- The number has gradually increased due to advancements in low-frequency radio telescopes like GMRT and LOFAR, but the discovery of 34 new sources at once is a substantial addition to this growing list.
- Challenging Existing Theories:
- Some of the newly discovered GRSs were found in environments that challenge the conventional understanding that these sources grow only in low-density environments.
- Specifically, two of the GRSs (J0843+0513 and J1138+4540) were located in denser galaxy cluster environments, suggesting that environmental factors alone may not determine the size of these radio sources.
- Insights into Cosmic Structures:
- GRSs provide a unique opportunity to study the intergalactic medium and the large-scale structure of the universe.
- Their massive size and powerful radio emissions can reveal the distribution and behavior of matter in the cosmos, offering clues about the interaction between supermassive black holes and their host galaxies.
- Understanding Radio Galaxy Evolution:
- The discovery of these GRSs aids in understanding the late stages of radio galaxy evolution.
- As radio sources grow larger, their lobes become more difficult to detect, particularly at higher frequencies.
- The GMRT’s low-frequency observations allow astronomers to identify these sources, even when the connecting emissions are faint or absent.
- Expansion of Known GRS Population:
Radio Galaxies
- Radio galaxies emit intense radio waves originating from expansive lobes of gas, extending millions of light-years beyond the visible galaxy structure.
- These lobes, typically occurring in pairs, are a consequence of AGNs—regions of extraordinary brightness where supermassive black holes actively consume surrounding matter, emitting glowing radiation.
- Around 15% to 20% of galaxies hosting AGNs exhibit “radio loud” characteristics, as distinguished by their prominence in radio emissions.
- The differentiation between “radio loud” and “radio quiet” AGNs remains an ongoing area of investigation due to similarities in emissions across various wavelengths.
- Research hints at potential connections between radio loudness and the type of host galaxy.
- Notably, radio galaxies predominantly manifest in the form of massive elliptical galaxies, possibly formed through mergers of smaller galaxies.
- Additionally, the rotational dynamics of central black holes may contribute to the formation of powerful jets, influencing radio emissions.
- Prominent instances of radio galaxies include:
- Cygnus A, exhibiting bright lobes of gas surrounding a galactic nucleus;
- Messier 87, characterized by twin jets emanating from a luminous core; and
- Centaurus A, an elliptical galaxy intersected by a dust lane.
- Distinctive optical emissions define two types of radio galaxies:
- Broad-line radio galaxies: Broad-line radio galaxies display broad-line emissions from ionized oxygen, hydrogen, and silicon in their optical spectra.
- Narrow-line radio galaxies: Whereas narrow-line radio galaxies lack such emissions but showcase narrow emission lines from hydrogen and oxygen.
Giant Radio Sources (GRSs)
- Giant Radio Sources (GRSs) are among the largest objects in the universe, with sizes extending over several megaparsecs.
- These astronomical phenomena are powered by supermassive black holes at the centers of galaxies, which emit jets of ionized material that generate massive lobes of radio emissions far beyond the visible size of their host galaxies.
- GRSs are considered to represent the late stages of radio galaxy evolution, and their sheer size and rarity make them critical for understanding the dynamics of the universe, the evolution of galaxies, and the behavior of matter on a cosmic scale.
The Role of the Giant Metrewave Radio Telescope (GMRT)
- Located near Khodad village, approximately 90 km north of Pune, the Giant Metrewave Radio Telescope (GMRT) is one of the world’s most powerful radio telescopes, specifically designed to observe at low frequencies.
- It is built and operated by the National Centre for Radio Astrophysics (NCRA) of the Tata Institute of Fundamental Research (TIFR).
- The GMRT is instrumental in mapping the radio sky and identifying radio sources that are not easily detectable at higher frequencies.
The TIFR GMRT Sky Survey (TGSS)
- Between 2010 and 2012, the GMRT was utilized for the TIFR GMRT Sky Survey (TGSS), which aimed to map the sky at a frequency of 150 MHz, covering about 90% of the sky.
- This survey was crucial for identifying faint and distant radio sources, including the giant radio sources that are often missed by other radio surveys due to their low surface brightness and extended structure.
Expert Opinions and Future Research
- Dean of the GMRT Observatory at NCRA-TIFR, emphasized the importance of this discovery in understanding the evolution of radio galaxies.
- The observational challenges of detecting large radio sources have historically limited the number of known GRSs.
- However, with the commissioning of new telescopes like GMRT, astronomers can now identify many more such sources.
- The enormous size and powerful radio emissions of these galaxies provide insights into the large-scale structure of the universe and the relationship between black hole activity and galaxy evolution.
Future Directions
- The research team plans to continue their work by presenting new samples of giant radio galaxies (GRGs) in forthcoming studies.
- These studies will include detailed physical properties based on multi-wavelength observations, aiming to unravel the mysteries surrounding the formation and evolution of these colossal structures.
