RAD@home citizen science discovery of a Supersonic Radio Galaxy: Cosmic Bow and Arrow (RAD-BAARG)

हिंदी

An international team of astronomers working with RAD@home Astronomy Collaboratory for citizen science research in India has discovered a remarkable “bow-and-arrow”-shaped radio galaxy using ultra-sensitive images from the LOFAR radio telescope. The newly identified system exhibits an enormous arc-like structure extending nearly 1.8 million light years across and may represent one of the clearest known radio signatures of a giant bow-shock generated by a galaxy falling supersonically into a cluster environment.Image

Image Caption: Bow-and-arrow-shaped radio galaxy (RAD-BAARG), with the 144 MHz radio image from the LOFAR radio telescope shown in red and the optical image from the BASS survey shown in RGB colour. Credit: Hota et al. (2026) and the RAD@home Collaboratory.

An artistic animation of the formation mechanism of RAD-BAARG can be seen here  https://youtu.be/kHu46vgeB4Y

The discovery was made using data from the LOFAR Two-metre Sky Survey (LoTSS), one of the deepest radio surveys ever conducted at low frequencies. The source, named RAD-BAARG (Bow-And-Arrow Radio Galaxy), displays a highly unusual and asymmetric structure unlike those seen in standard radio galaxies.

Radio galaxies are powered by supermassive black holes located at the centres of galaxies. These black holes launch enormous jets of relativistic magnetised plasma into intergalactic space. In RAD-BAARG, one of the jets appears to interact with a large bow-shock-like structure formed as the host galaxy falls through the surrounding hot gas toward a nearby cluster of galaxies.

Similar to the shock wave formed ahead of a supersonic aircraft, a galaxy moving faster than the speed of sound in the surrounding intracluster medium can compress the ambient gas and generate a large-scale shock front. The radio-emitting plasma from RAD-BAARG appears to illuminate this otherwise extremely faint structure, making it visible in low-frequency radio images.

The western side of the source contains a narrow jet feeding a sector-shaped emission region and a giant arc-like feature extending over nearly 560 kiloparsecs (1.8 million light years). On the opposite side, the jet develops a distorted S-shaped morphology followed by a faint offset tail extending to almost 600 kiloparsecs. The overall structure suggests strong interaction between the radio plasma and the surrounding large-scale environment.

The research team found that the host galaxy resides within a dynamically complex environment containing nearby cluster-scale systems at similar distances. The observed morphology is consistent with interaction between the radio jets and large-scale environmental gradients, bulk gas motions, and possible shock-related compression associated with the galaxy’s infall.

Although theoretical studies and computer simulations have long predicted bow shocks around infalling galaxies, detecting them directly has proven extremely difficult because the surrounding gas is extraordinarily diffuse and faint. A few candidate systems have previously been hinted at in X-ray observations, but RAD-BAARG provides an unusually detailed radio view of such a phenomenon.

“The structure of this source is unlike that of any radio galaxy I have seen since the last 25 years,” says Dr. Ananda Hota, founder Director and Principal Investigator of RAD@home Astronomy Collaboratory, and lead author “Its remarkable morphology appears to display signatures of interaction between relativistic radio plasma and a large-scale shock generated during the galaxy’s infall into a nearby cluster environment.”

Dr Pratik Dabhade another lead author from the National Centre for Nuclear Research (Poland) says “BAARG is exciting not just because of its striking bow-and-arrow shape, but because it sits in a complex multi-halo environment where gas flows, infall, and possible shocks can reshape radio plasma. LOFAR allows us to see this faint, low-surface-brightness emission in remarkable detail. With LoTSS DR3 and the future SKAO, we may find many more systems where radio galaxies reveal otherwise invisible interactions between jets, galaxies, and their environments.”

Adding to this, one of the other leading authors Dr Shubhrangshu Ghosh of Center for Astrophysics, Gravitation and Cosmology (CAGC) of SRM University Sikkim, India says “the reported observation reveals the first direct imaging of characteristic arc-shape morphology in radio frequency in regard to supersonically infalling radio-galaxy (most likely) onto a cluster medium - a spectacular text book example of large bow-shock. Discovery of more such sources and their study during the SKA era will provide much deeper insight about jet-ambient medium interaction and consequent feedback processes.

Describing about shocks Dr Chiranjib Konar of Amity University (Noida) and professional member of the Collaboratory says "This type of large bow structure around the head of the astrophysical radio jets has never been seen before. Across the bow structure there would be sudden jumps in the temperature, pressure, density and magnetic field strength with the higher values in the inner side of the bow."

The unusual source was initially noticed by RAD@home citizen scientist Mr. Pranim Limbo while visually inspecting LOFAR survey images. Coming from a remote Himalayan hill region and without access to a major astronomy institute, the discovery highlights the power of collaboratory-style citizen science research, initiated by RAD@home, in enabling university students and motivated learners to participate directly in front-line astronomical research.

Since 2013, RAD@home has trained participants across India to analyse astronomical data from world-class telescopes and contribute to professional scientific discoveries irrespective of their geographic or institutional backgrounds.

My Limbo says “I sincerely thank RAD@home for providing a unique platform to learn radio astronomy through online weekend e-classes, mentorship, and hands-on research with multi-wavelength data. Their guidance and collaborative approach helped me develop research skills and contribute to scientific work leading to this publication.”

The discovery also points toward exciting future possibilities for next-generation radio astronomy facilities such as the Square Kilometre Array Observatory (SKAO), currently under construction and expected to become the world’s most powerful radio telescope. Future ultra-sensitive surveys may uncover many more examples of shock-related interactions around infalling galaxies and help astronomers better understand how radio galaxies evolve within the large-scale cosmic environment.

The team also expects that artificial intelligence and machine-learning techniques can now be trained using such rare morphologies to identify additional unusual radio galaxies hidden within the enormous data volumes expected from upcoming radio sky surveys.

Other than Drs Hota, Dabhade, Ghosh, Konar and Mr Limboo, the discovery team includes Dr Sagar Sethi (University of Warmia and Mazury, Poland), Mr Souvik Manik (Midnapore City College, India), Mr Aditya Sahasranshu (RAD@home), Dr. Sabyasachi Pal (Midnapore City College, India), Dr. Mitali Damle (New York University Abu Dhabi, UAE), Dr Sravani Vaddi (RAD@home) and Ms Arundhati Purohit (RAD@home). The research paper entitled “RAD@home discovery of a bow-and-arrow radio galaxy tracing a ∼560 kpc bow-shock structure in a multi-halo environment” has just been published in the Letters of the Monthly Notices of the Royal Astronomical Society, by the Oxford University Press (DOI: 10.1093/mnras/stag1033).

Science Contact: Dr Ananda Hota ( RADatHomeIndia _AT-SIGN_ gmail DOT com )

(Founder Director and Principal Investigator, RAD@home, India
UGC faculty @ CEBS & CETACS, University of Mumbai, India)

Link to the Royal Astronomical Society (RAS, UK) Press Release https://ras.ac.uk/news-and-press/research-highlights/bow-and-arrow-shaped-radio-galaxy-discovered-citizen-scientist

National Centre for Nuclear Research (NCBJ, Poland) Press release here https://www.ncbj.gov.pl/en/news/cosmic-bow-and-arrow-supersonic-radio-galaxy-tracing-giant-bow-shock

………………………….........................

To subscribe to our future Press Releases and News Letters, Press and media-friends (journalists/science-communicators) can fill the Google form here

https://docs.google.com/forms/d/e/1FAIpQLSf78SMI2x9Zhl6gvBLzN4Ea5xPZ1RoHprJ231V9KVT7gnz8NA/viewform

=============================