An Indian team has discovered a rare bow-and-arrow radio galaxy two billion light-years from Earth

Twelve Indian researchers in three countries have discovered a rare bow-and-arrow-shaped anomalous radio galaxy 1.8 million light-years across, located approximately 2 billion light-years from Earth.

A light-year is about 5.88 trillion miles. Powered by supermassive black holes at its core, a radio galaxy is a type of active galaxy that emits very large amounts of energy in the form of radio waves.

The newly discovered arc system has been named RAD-BAARG where RAD stands for RAD@home Astronomy Collaboratory, India’s first citizen science research platform in astronomy based at Kharghar in Navi Mumbai. BAARG expands to Bow And Arrow Radio Galaxy.

The research team’s paper, titled “RAD@home discovery of a bow-and-arrow radio galaxy tracing the ~560-kpc bow shock structure in a multi-halo environment,” was published in Monthly Notices of the Royal Astronomical Society on June 22. According to this paper, radio galaxies are “highly unusual” and asymmetric unlike those found in standard radio galaxies.

Kpc is short for kiloparsec, a unit of astronomical distance equal to 1,000 parsecs, or about 3,260 light years.

The study’s lead author is Ananda Hota of the University of Mumbai and founder-director of 13-year-old RAD@home, which enables university students and others to conduct extragalactic research and astronomical discoveries from the comfort of their homes.

The other authors – all associated with RAD@home – are Pratik Dabhade of the Poland-based National Center for Nuclear Research; Shubhrangshu Ghosh of Sikkim’s Shri Ramasamy Memorial University (SRM); Mitali Damle of New York University Abu Dhabi; Souvik Manik and Sabyasachi Pal from Midnapore City College, West Bengal; C. Konar of Noida-based Amity University; Sagar Sethi of Poland’s University of Warmia and Mazury; and Pranim Limbo, Aditya Sahasranshu, Sravani Vaddi and Arundhati Purohit.

Supersonic fall

RAD-BAARG was found using ultra-sensitive images from the LOFAR (Low Frequency Array) Two Meter Sky Survey, one of the deepest radio surveys ever conducted at low frequencies. Its discovery follows the identification of the most distant and powerful Odd Radio Circle known to the team at the time in 2025.

According to Mr. Ghosh, supermassive black holes in radio galaxies release huge jets of relativistic magnetized plasma into intergalactic space. In RAD-BAARG, one of the jets appears to interact with a large shock-like structure formed as the host galaxy falls through the surrounding hot gas towards a nearby galaxy cluster.

“Much like a shock wave created in front of a supersonic jet, a galaxy moving faster than the speed of sound in the surrounding medium inside the cluster can compress the surrounding gas to form an extensive 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,” Mr Ghosh told The Hindu.

“The western side of the source contains a narrow jet feeding the sector-shaped emission region and a giant arc-like feature that extends across nearly 560 kpc (1.8 million light-years). On the opposite side, the jet has a distorted S-shaped morphology followed by a faint offset tail reaching nearly 600 kpc. The overall structure suggests a strong interaction between the large-scale radio environment.

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

Infall refers to the inward motion of gas, dust, or cosmic bodies caused by gravity toward a massive object.

Also read | The Bombay-led team helps uncover the mysterious double rings around the galaxy

Clearest radio signatures

“Although theoretical studies and computer simulations have long predicted shocks around infalling galaxies, their direct detection has proven extremely difficult because the surrounding gas is extremely diffuse and faint. RAD-BAARG provides an unusually detailed radio view of such a phenomenon,” said Mr Ghosh.

“The structure of this source is unlike any radio galaxy I have seen in the last 25 years. Its remarkable morphology appears to show signs of interaction between the relativistic radio plasma and the large-scale shock generated during the galaxy’s impact into the nearby cluster environment,” said Mr Hota.

“BAARG is exciting not only because of its striking bow-and-arrow shape, but also because it is in a complex, multi-halo environment where gas flows, impacts and eventual shocks can reshape the radio plasma,” Mr Dabhade said.

The researchers said LOFAR helped them see the faint, low-surface-brightness RAD-BAARG emission in “remarkable” detail. They hoped that next-generation radio astronomy facilities, including the Square Kilometer Array Observatory under construction, would facilitate a better understanding of how radio galaxies evolve in the large cosmic environment.

The team also proposed using artificial intelligence and machine learning techniques to identify other unusual radio galaxies hidden in the huge volumes of data expected from upcoming surveys of the radio sky.

Published – 03 Jul 2026 0:36 IST