Astronomers discover rare double-ringed odd radio circle in space

An unusual double-ring structure spotted in space with the help of citizen scientists has turned out to be a cosmic rarity.

The celestial anomaly, captured by a radio telescope, is an odd radio circle, one of the scarcest and most mysterious objects in the universe, said Dr. Ananda Hota, lead author of a study published on October 2 in the Monthly Notices of the Royal Astronomical Society.

Odd radio circles, also known as ORCs, likely consist of magnetized plasma — charged gas that is strongly influenced by magnetic fields — and are so massive that entire galaxies reside at their centers. Spanning hundreds of thousands of light-years, they often reach 10 to 20 times the size of our Milky Way galaxy. But they are also incredibly faint, and usually detectable only through radio light.

The newly discovered odd radio circle, dubbed RAD J131346.9+500320, is the most distant one known to date, located 7.5 billion light-years from Earth — and the first discovered by citizen scientists. It’s also only the second odd radio circle that has two rings.

“ORCs are among the most bizarre and beautiful cosmic structures we’ve ever seen — and they may hold vital clues about how galaxies and black holes co-evolve, hand-in-hand,” wrote Hota, an assistant professor at the University of Mumbai’s department of atomic energy’s Centre for Excellence in Basic Sciences, in an email.

A giant leap for citizen science

Odd 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 background in science. Astronomers train users to recognize patterns in faint, fuzzy patches of radio waves and analyze astronomical images, Hota explained.

The newly discovered odd radio circle appeared in data from the Low Frequency Array (LOFAR) Telescope, which is comprised 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.

While RAD@home participants weren’t specifically trained to look for odd radio circles, the unusual double-ring structure stood out, marking the first odd radio circle identified using LOFAR. The rings appear to intersect which researchers believe is because of our vantage point from Earth, but they are likely separated in space. The pair span 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 together can push the boundaries of scientific discovery,” Hota said.

Astronomers once thought the odd radio circles might be the throats of wormholes, shockwaves from black hole collisions or merging galaxies, or powerful jets pumping out energetic particles.

“We suggest that a major explosive event took place in the central galaxy,” Hota said. “The resulting shock or blast wave could have re-energised ancient clouds of magnetised plasma, making them glow again as radio rings.”

The plasma clouds were likely first created by jets of material released by the galaxy’s supermassive black hole, Hota explained. A new shockwave essentially illuminated “smoke” left behind by the galaxy’s past activity, he added.

Black holes don’t directly gobble up stars, gas and dust. Instead, that material falls into a rotating disk around the black hole. As the debris spirals more rapidly, it becomes superheated. The powerful magnetic fields around black holes help channel these energetic, superheated particles away from black holes in jets that nearly reach the speed of light.

The citizen science team also spotted two additional odd radio circles in two different galaxies, including one located at the end of a powerful jet that has a sharp curve, resulting in a radio ring about 100,000 light-years wide.

Both odd radio circles are in galaxies that sit within larger clusters of galaxies, meaning the jets launching 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 shaped by black hole jets, winds, and their environments,” said study coauthor Dr. Pratik Dabhade, assistant professor in the astrophysics division of the National Centre For Nuclear Research in Warsaw, Poland, in a statement.

Ray Norris, an astrophysicist at Australia’s Commonwealth Scientific and Industrial Research Organisation who led the discovery of odd 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 spot odd radio circles because there are so few known examples, he said.

“ORCs are really hard to find, but we know there must be hundreds in the data,” Norris said. “At the moment, citizen science look like the best approach and these guys seem to be making a great job of it.”

Lingering galactic puzzles

The discovery of the most distant odd radio circle to date lets researchers effectively look back in time. The team believes that the phenomenon may serve as a way of recording and preserving ancient, violent events that shaped galaxies billions of years ago.

The light from the radio circle has traveled for 7.5 billion years to reach Earth and could provide insights into the roles that odd radio circles play in the evolution of galaxies over different timescales, which is not well known.

“By studying them across different cosmic times, we can begin to reveal how such energetic outbursts influence the surrounding gas and trigger or suppress star formation,” Hota noted. “Our discovery pushes the known boundary of ORCs to nearly half the age of the Universe, providing vital clues about their origins and link to the broader life cycle of galaxies.”

Many questions linger about odd radio circles, including why astronomers only see them at such large sizes. Hota and Dabhade want to know whether the circles expand from smaller bubbles that are undetectable. And if odd radio circles do spring from the mergers of galaxies or supermassive black holes, why aren’t they spotted more frequently?

The help of citizen scientists, and next-generation telescopes like the transcontinental Square Kilometre Array in South Africa and Australia, will be needed to answer such questions.

Now under construction and expected to be completed in 2028, the array will include thousands of dishes and up to a million low-frequency antennas to create the world’s largest radio telescope.

Even though these dishes and antennas will be in two different parts of the world, they will form one telescope with more than 1 million square meters (386,102 square miles) of collecting area, allowing astronomers to survey the entire sky much more quickly than ever before.

The SKA, and other telescopes in development, will be able to observe the odd radio circles in much greater detail, helping astronomers learn more about the evolution of black holes and galaxies.

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