Space’s rarely visible giants

Indian astronomers detect a number of Giant Radio Galaxies, hope it will be a step towards a better understanding of why they are so huge, so rare

Giant Radio Galaxies, new galxies discovered, new planets discovered, Indian astronomers, Pune Inter University Centre for Astronomy and Astrophysics

The researchers, whose findings have been published in Monthly Notices of the Royal Astronomical Society, are now aiming at a better understanding of the physical properties of these radio giants.

A team of Indian astronomers, including from Pune-based Inter University Centre for Astronomy and Astrophysics, has reported that they have detected a large number of an extremely rare kind of galaxies, called Giant Radio Galaxies, using data from a 20-year-old, highly sensitive radio survey. The researchers, whose findings have been published in Monthly Notices of the Royal Astronomical Society, are now aiming at a better understanding of the physical properties of these radio giants.

A radio galaxy is a kind of active galaxy, which in turn differs from a typical galaxy on account of its core of emission, called an active galactic nucleus. A radio galaxy is an active galaxy that emits large amounts of radio waves, powered by the galaxy’s supermassive black hole. Giant radio galaxies, or GRGs, are the largest kind, spanning 3 million light years or more — the equivalent of stacking 33 Milky Way-sized galaxies in a straight line.

GRGs are visible only to radio telescopes and hence hard to detect. The first such galaxy was found in 1974, followed by about 300 more since then. The team at IUCAA has identified several hundred candidates, and confirmed the first 25 as radio galaxies, some of them up to 10 million light years across. “Our work will help in understanding how these galaxies grow to be so large,” said lead author Pratik Dabhade, a junior research fellow under the Indo-French Centre for the Promotion of Advanced Research project at IUCAA and a PhD student at the Observatory of Leiden, Netherlands.

“We are studying whether they are born in regions of very sparse galaxy density or they have extremely powerful and long-lasting radio jets which allow them to expand to very huge distances,” Dabhade told The Indian Express from the Netherlands. Researchers have been working on finding and studying rare species of radio galaxies for insights into how these galaxies produce energy at their centres and transfer it to the medium outside the galaxy.

The team of Indian scientists includes Joydeep Bagchi (IUCAA) Madhuri Gaikwad (Max Planck Institute, Bonn), Shishir Sankhyayan (IISER, Pune), Mamta Pommier (CNRS Observatoire de Lyon) and Somak Raychaudhury (IUCAA director). “The astronomers benefited from the generous support from the Indo-French Centre for the Promotion of Advanced Research,” Dabhade said. It has been working with a set of 300 large images from the US National Radio Astronomy Observatory’ Very Large Array survey more than 20 years ago. They inspected these images over almost two years to identify many giant radio galaxies.

“After finding them in radio images, we have to find their counterparts in the optical domain,” Dabadhe said. These have to be followed by comparison, and deeper observations with other radio telescopes such as the Giant Metrewave Radio Telescope near Pune, to confirm the GRGS’ existence. “When we point a normal (optical) telescope at these galaxies, we image the starlight from them,” Raychaudhury described the search. “However, telescopes that can observe other forms of radiation and energy, such as radio waves and X-ray radiation, can image components of these galaxies other than stars… Radio telescopes can image the really fast-moving charged particles in a galaxy, which are associated with high energy outflow at the centres of galaxies where a supermassive black hole exists. These emit a form of radiation known as synchrotron radiation, which can be seen by radio telescopes.”

These particles, mostly electrons, move at speeds close to the speed of light and show up as thin jets shooting out of the centre of the galaxy. These outflows last for millions of years, during which these particles reach outside the galaxy, culminating into lobes as they lose energy. In most cases these jets are the same size as the galaxies themselves. There are two big mysteries about GRGs: Why they are so big, and why they are apparently rare.

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Discovering more GRGs, the astronomers said, will allow them to study them with other multi-wavelength telescopes to find out their age, central black hole mass, star formation rate etc. Among the answers scientists are looking for are: Are these galaxies in which the black holes emit more energy than in others? Are these galaxies sitting in an under-dense environment such that the jet travel to larger distances? Do the energetic particles give rise to other physical effects by themselves that make them longer-lived and hence enable them to travel very far?

Anuradha Mascarenhas

Anuradha Mascarenhas is a Senior Editor at The Indian Express, based in Pune. With a career spanning three decades, she is one of the most respected voices in Indian journalism regarding healthcare, science and environment and research developments. She also takes a keen interest in covering women's issues . Professional Background Education: A gold medalist in Communication and Journalism from Savitribai Phule Pune University and a Master’s degree in Literature. Author: She authored the biography At The Wheel Of Research, which chronicles the life and work of Dr. Soumya Swaminathan, the former Chief Scientist at the WHO. Key Focus: She combines scientific accuracy with storytelling, translating complex medical research into compelling public and human-interest narratives. Awards and Recognition Anuradha has won several awards including the Press Council of India's national award for excellence in journalism under the gender based reporting category in 2019 and the Laadli Media award (gender sensitivity -2024). A recipient of the Lokmat journalism award (gender category-2022), she was also shortlisted for the RedInk awards for excellence in journalism-2021. Her debut book At The Wheel Of Research, an exclusive biography of Dr Soumya Swaminathan the inaugural chief scientist of World Health Organisation was also nominated in the Popular Choice Category of JK Paper AUTHER awards. She has also secured competitive fellowships including the Laadli Media Fellowship (2022), the Survivors Against TB – New Research in TB Media Fellowship (2023) and is part of the prestigious 2025 India Cohort of the WomenLift Health Leadership Journey.” Recent Notable Articles (Late 2025) 1. Cancer & Specialized Medical Care "Tata Memorial finds way to kill drug-resistant cancer cells" (Nov 26, 2025): Reporting on a breakthrough for triple-negative breast cancer, one of the most aggressive forms of the disease. Discipline, diet and purpose; How a 97-year-old professor defies ageing'' (Nov 15, 2025) Report about Prof Gururaj Mutalik, the first Head of Department at Pune's B J Government Medical College who at 97 credits his longevity to healthy habits and a strong sense of purpose. 2. Environmental Health (The "Breathless Pune" Series) Long-term exposure even to 'moderate' air leads to chronic heart, lung, kidney issues" (Nov 26, 2025): Part of an investigative series highlighting that even "safe" pollution levels are damaging to vital organs. "For every 10 µg/m3 increase in PM2.5 level, there was 6-8% jump in medicine sales" (Nov 23, 2025): Using commercial data to prove the direct link between air quality and respiratory illnesses in Pune. 3. Lifestyle & Wellness News "They didn't let cancer, diabetes and heart disease stop them from travelling" (Dec 22, 2025): A collaborative piece featuring survivors who share practical tips for traveling with chronic conditions. At 17, his BP shot up to 200/120 mmHG; Lancet study flags why child and teen hypertension doubled between 2000 and 2020'' (Nov 12,2025)--A report that focusses on 17-year-old-boy's hypertensive crisis and reflects the rising global trend of high blood pressure among children and adolescents. 4. Scientific Recognition & Infrastructure For promoting sci-comm, gender diversity: IUCAA woman prof highlighted in Nature" (Nov 25, 2025): Covering the global recognition of Indian women scientists in gender studies and physics. Pune researchers find a spiral galaxy like the Milky Way from early universe'' (December 3, 2025)- A report on how Indian researchers discovered a massive galaxy that existed when the universe was just 1.5 billion years old , one of the earliest to have been observed so far. Signature Beat: Health, Science & Women in Leadership Anuradha is known for her COVID-19 reportage, where she was one of the first journalists to provide detailed insights into the Covishield and Covaxin trials. She has a dedicated interest in gender diversity in health and science, often profiling women researchers who are breaking the "leaky pipeline" in STEM fields. Her writing style is scrupulous, often featuring interviews with top-tier scientists and health experts from various institutions. ... Read More

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