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Bow-and-arrow-shaped radio galaxy discovered by citizen scientist

RAD-BAARG radio galaxy, 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.<br>Credit<br>Hota et al. (2026) and the RAD@home Collaboratory

Licence type<br>Attribution (CC BY 4.0)

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Astronomers have discovered a “remarkable” bow-and-arrow-shaped radio galaxy with an enormous arc-like structure extending nearly 1.8 million light-years across.<br>The newly-identified system, detailed in a new paper published today in Monthly Notices of the Royal Astronomical Society: Letters has a “highly unusual” and asymmetric structure which is unlike those seen in standard radio galaxies.<br>It was detected by an international team of researchers working with RAD@home Astronomy Collaboratory for citizen science research in India using ultra-sensitive images from the Low-Frequency Array (LOFAR) radio telescope.<br>They say it may represent one of the clearest known radio signatures of a giant bow shock generated by a galaxy falling supersonically into a cluster environment.<br>“The structure of this source is unlike that of any radio galaxy I have seen in the last 25 years,” said lead author Dr Ananda Hota, Founder, Director and Principal Investigator of RAD@home Astronomy Collaboratory.<br>“It’s 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.”<br>The discovery of the source – named RAD-BAARG (Bow-And-Arrow Radio Galaxy) – was made using data from the LOFAR Two-metre Sky Survey (LoTSS), one of the deepest radio surveys ever conducted at low frequencies.<br>Radio galaxies are powered by supermassive black holes located at the centres of galaxies which launch enormous jets of relativistic magnetised plasma into intergalactic space.<br>In RAD-BAARG, the researchers say 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.<br>Similar to the shockwave 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.<br>The radio-emitting plasma from RAD-BAARG appears to illuminate this otherwise extremely faint structure, making it visible in low-frequency radio images, according to the team. 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).<br>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.<br>The research team found that the host galaxy resides within a dynamically complex environment containing nearby cluster-scale systems at similar distances.<br>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.<br>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.<br>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.<br>Co-lead author Dr Pratik Dabhade, from the National Centre for Nuclear Research in...