by An unusual double ring structure discovered in space with the help of citizen scientists has proven to be a cosmic rarity.
The celestial anomaly, captured by a radio telescope, is a strange radio circle, one of the scarcest and most mysterious objects in the universe, said Dr. Ananda Hota, lead author of a study published Oct. 2 in the Monthly Notices of the Royal Astronomical Society.
Strange radio circles, also known as ORCs, are likely composed of magnetized plasma – charged gas strongly influenced by magnetic fields – and are so massive that entire galaxies reside at their centers. They span hundreds of thousands of light years and are often 10 to 20 times the size of our Milky Way Galaxy. But they are also incredibly faint and usually only detectable through radio light.
The newly discovered strange radio circle, named RAD J131346.9+500320, is the most distant yet known, located 7.5 billion light-years from Earth – and the first discovered by citizen scientists. It is also only the second strange radio circle to have two rings.
“ORCs are among the most bizarre and beautiful cosmic structures we have ever seen — and they may hold crucial clues about how galaxies and black holes evolve hand in hand,” Hota, an assistant professor at the Center for Excellence in Basic Sciences at the University of Mumbai’s Department of Atomic Energy, wrote in an email.
A giant leap forward for citizen science
Strange radio circles were first discovered about six years ago, but the structures remain largely elusive.
Hota is the director and principal investigator of the RAD@home Astronomy Collaboratory, an online community open to anyone with a scientific background. Astronomers train users to recognize patterns in faint, faint spots of radio waves and analyze astronomical images, Hota explains.
The newly discovered strange radio circle appeared in data from the Low Frequency Array (LOFAR) Telescope, which consists of thousands of antennas in the Netherlands and across Europe to create one large radio telescope. It is the largest and most sensitive radio telescope operating at low frequencies.
Although RAD@home participants were not specifically trained to look for strange radio circles, what stood out was the unusual double ring structure, marking the first strange radio circle identified using LOFAR. The rings appear to intersect, which researchers say is due to our vantage point from Earth, but they are likely separated in space. The pair is 978,469 light-years across. A light year is the distance light travels in one year, or 5.88 trillion miles (9.46 trillion kilometers).
“This work shows how professional astronomers and citizen scientists can work together to push the boundaries of scientific discovery,” Hota said.
Astronomers once thought the strange radio circles might be the throats of wormholes, shock waves from collisions between black holes or merging galaxies, or powerful jets pumping out energetic particles.
“We suggest that a large explosive event has occurred in the central galaxy,” Hota said. “The resulting shock or explosion wave could energize old clouds of magnetized plasma, causing them to glow again when radio signals sound.”
The plasma clouds were likely first created by jets of material released by the Milky Way’s supermassive black hole, Hota explained. A new shock wave essentially illuminated “smoke” left behind by the Milky Way’s past activity, he added.
The double-ringed odd radio circle can be seen in radio light as observed by LOFAR. – RAD@home Astronomy Collaboratory (India)
Black holes do not directly swallow stars, gas and dust. Instead, that material falls into a rotating disk around the black hole. As the debris spirals faster, it overheats. The powerful magnetic fields around black holes help channel these energetic, superheated particles away from black holes into jets that travel nearly the speed of light.
The citizen science team also discovered two additional strange radio circles in two different galaxies, including one at the end of a powerful jet with a sharp bend, resulting in a radio ring about 100,000 light-years wide.
Both strange radio circles are located in galaxies that are within larger galaxy clusters, meaning the jets launched from their supermassive black holes interact with surrounding hot plasma that could help shape the radio rings, Hota said.
“These discoveries show that ORCs and radio rings are not isolated curiosities – they are part of a broader family of exotic plasma structures formed by black hole jets, winds and their environments,” said co-author Dr. Pratik Dabhade, assistant professor at the Department of Astrophysics at the National Center for Nuclear Research in Warsaw, Poland, said in a statement.
Ray Norris, an astrophysicist at Australia’s Commonwealth Scientific and Industrial Research Organization who led the discovery of strange radio circles, was pleased to see a discovery of the phenomenon using the LOFAR telescope – and with citizen science.
It’s difficult to train AI to recognize strange radio rings because there are so few known examples, he said.
“ORCs are very difficult to find, but we know there are hundreds of them in the data,” Norris said. “Right now, citizen science seems like the best approach and these guys seem to be doing a great job with it.”
Persistent galactic puzzles
The discovery of the most remote strange radio circle yet allows researchers to effectively look back in time. The team believes the phenomenon could serve as a way to record and preserve ancient, violent events that formed galaxies billions of years ago.
The light from the radio circle has traveled 7.5 billion years to reach Earth and could provide insight into the role that strange radio circles play in the evolution of galaxies on different timescales, which is not yet well understood.
“By studying them at different cosmic times, we can begin to reveal how such energetic outbursts affect the surrounding gas and induce or suppress star formation,” Hota noted. “Our discovery pushes the known limit of ORCs to almost half the age of the Universe, providing vital clues about their origin and connection to the broader life cycle of galaxies.”
Many questions remain about strange radio circles, including why astronomers only see them at such large sizes. Hota and Dabhade want to know if the circles expand from smaller bubbles that cannot be observed. And if strange radio circles arise from the merger of galaxies or supermassive black holes, why aren’t they noticed more often?
The help of citizen scientists and next-generation telescopes, such as the transcontinental Square Kilometer Array in South Africa and Australia, will be needed to answer such questions.
The array, now under construction and expected to be completed in 2028, will include thousands of dishes and up to a million low-frequency antennas to create the world’s largest radio telescope.
Although these dishes and antennas will be located in two different parts of the world, they will form one telescope with a collecting area of more than 1 million square meters (386,102 square miles), allowing astronomers to survey the entire sky much faster than ever before.
The SKA and other telescopes in development will be able to observe the strange radio circles in much more detail, allowing astronomers to learn more about the evolution of black holes and galaxies.
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