Astronomers identify bow-and-arrow-shaped radio galaxy tracing shock 1.8 million light years away
An intriguing radio galaxy recently discovered by a citizen scientist surprised astronomers by displaying a unique “bow and arrow” configuration. This unprecedented formation could offer crucial information about how galaxies are altered by gigantic shock waves, generated when they pass through cosmic clusters at extreme speeds.
The object, called RAD-BAARG (Radio Bow-And-Arrow Radio Galaxy), spans almost 1.8 million light-years, which means it is approximately 18 times the size of the Milky Way. Its peculiar morphology was first identified by a volunteer at the RAD@home Astronomy Collaboratory, an initiative that empowers citizens to analyze data from telescopes and point out anomalies that could go unnoticed by conventional methods.
Celestial observers said they had never seen anything like this before. Ananda Hota, from the University of Mumbai, highlighted in a statement released by the Royal Astronomy Society that the structure of RAD-BAARG differs from any other radio galaxy he has seen in his 25-year career. The statement also suggests that the discovery may represent “one of the clearest radio signatures” of a monumental shock wave, caused by a galaxy hurtling at high speed through a cluster.
After the revelation, researchers undertook detailed studies of the structure, using data from the LOFAR (Low Frequency Array) Two-meter Sky Survey (LoTSS). This low-frequency radio survey is one of the most complete ever carried out, ideal for detecting weak and scattered radio emissions in space.
Unlike ordinary radio galaxies, which usually emit two symmetrical jets of charged particles from supermassive black holes, RAD-BAARG shows a marked asymmetry. One of its jets forms a wedge-shaped area that bends backwards in a vast arc, while the other contorts into an “S” shape before dissipating into an extensive tail. Together, these characteristics resemble the figure of a bow with an arrow, as described in the statement.
The plasma emitting radio waves from RAD-BAARG appears to illuminate a vast and extremely subtle configuration that would otherwise be invisible. At low radio frequencies, ancient, diffuse populations of electrons become more noticeable, which allows astronomers to track formations that would be imperceptible at higher optical or radio frequencies. This gives surveys like LoTSS exceptional power to identify and confirm these scattered emissions.
Scientists believe this remarkable asymmetry is directly linked to the galaxy’s displacement through a high-density galaxy cluster. As it moves toward the center of the cluster, the galaxy likely reaches supersonic speeds in the hot, rarefied gas present between the galaxies. This movement, crucial for the evolution of large cosmic structures, including the distribution of dark matter, is expected to generate a shock wave, compressing magnetic fields and charged particles, and thus reconfiguring the radio wave-emitting plasma into large structures.
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The research team also discovered that RAD-BAARG is situated in a complex “multi-halo” environment, which includes several overlapping reservoirs of heated gas. This condition makes the system an unusually valuable object of study for understanding how galaxy clusters influence radio galaxies.
Pratik Dabhade, co-lead author of the research and scientist at the Polish National Center for Nuclear Research, said in a statement that “LOFAR allows us to observe this faint, low-surface-brightness emission in rich detail.”
He added that with LoTSS DR3 and the future Square Kilometer Array Observatory (SKAO), it will be possible to identify a much larger number of systems where radio galaxies reveal hidden interactions between jets, other galaxies and their respective environments.
If its existence is fully confirmed, RAD-BAARG could establish itself as an exemplary case of how extreme conditions in galaxy clusters alter radio galaxies. The discovery promises to offer new insights into the interaction of supermassive black hole jets with their surroundings.
