In the vast, unfathomable darkness of space, astronomers have discovered something that defies both expectation and explanation: gigantic rings of radio light that seem to hang in the cosmic void. These structures, called Odd Radio Circles (ORCs), are unlike anything we’ve ever seen. Invisible to our eyes, undetectable in X-rays or infrared, they appear only when the universe is listened to in radio waves—giant, glowing halos that look as if the cosmos itself had drawn a circle in the night sky.
Now, astronomers from Ruhr University Bochum in Germany, working with colleagues across the globe, have taken a closer look at one such enigmatic structure: ORC J0356–4216. First identified in late 2023 with the powerful MeerKAT radio telescope in South Africa, this object has become the focus of an intense investigation. Using cutting-edge radio spectropolarimetric observations with MeerKAT and the Australian SKA Pathfinder (ASKAP), researchers have uncovered new details about this astonishing phenomenon. What they found pushes us closer to understanding ORCs—yet deepens the sense of wonder that surrounds them.
What Exactly Are Odd Radio Circles?
Odd Radio Circles are, quite literally, circles of radio light millions of light-years across. They are bright at the edges, faint in the middle, and highly circular in shape—unlike most cosmic structures, which tend to be irregular or chaotic. The first ORCs were discovered only a few years ago, and since then, only a handful have been identified. Their rarity makes them especially intriguing: we are looking at an entirely new class of astronomical objects.
But what makes them so strange is that they appear only in radio wavelengths. Point an optical telescope at their coordinates, and there is nothing—no glowing nebula, no cloud of dust, no visible star formation. They are ghosts in the electromagnetic spectrum, invisible except to the ears of radio astronomy.
The Discovery of ORC J0356–4216
In October 2023, astronomers spotted ORC J0356–4216 with MeerKAT, one of the world’s most sensitive radio telescopes. Almost immediately, it stood out: a double-ring structure, nearly two arcminutes across in the sky. At its measured distance—corresponding to a redshift of 0.494—this translates to a staggering 2.18 million light-years across. To put that into perspective, the Milky Way galaxy is about 100,000 light-years wide. ORC J0356–4216 is more than twenty times larger.
The rings are not random noise or transient flickers. They appear stable and symmetrical, forming what looks like a shell or shock front in deep space. Astronomers quickly focused their instruments on it, determined to peel back its secrets.
Listening to the Rings
The detailed study, led by Sam Taziaux of Ruhr University Bochum, involved measuring the radio emission of the rings at multiple frequencies. At 943 MHz, the two rings glowed with flux densities of 4.07 mJy and 2.82 mJy; at 1.28 GHz, they measured 2.77 mJy and 1.98 mJy. These numbers, though small, describe incredibly powerful emissions on cosmic scales.
The radio spectra revealed steep slopes, with spectral indices of -1.18 and -1.12, typical of non-thermal synchrotron radiation—energy produced when charged particles spiral through magnetic fields at near-light speeds. Even more fascinating was the discovery that the rings are polarized, with magnetic fields tangentially aligned along their circular rims. The degree of polarization reached 20–30%, suggesting an ordered, coherent magnetic structure spanning millions of light-years.
The total magnetic field strength was measured at around 1.82 and 1.65 microgauss. For comparison, Earth’s magnetic field is about 0.5 gauss—so these cosmic fields are millions of times weaker. Yet, stretched across such enormous scales, they shape and preserve the structure of these mysterious circles.
What Could Create Such a Structure?
The big question, of course, is why ORCs exist at all. They are too vast to be ordinary supernova remnants, too structured to be random noise, and too unique to fit into known categories of galactic phenomena. For ORC J0356–4216, two leading hypotheses stand out.
One possibility is that the rings are the lingering remains of a past active galactic nucleus (AGN) phase. Many galaxies, especially ellipticals, host supermassive black holes at their centers. When these black holes feed on surrounding gas, they unleash jets of energy and plasma that can blast far into space. If such jets switch on and off over time, they could leave behind massive radio lobes—relic echoes of their fury. The double-ring structure and polarization patterns of ORC J0356–4216 seem consistent with this explanation.
The second possibility is that the ORC was created by a giant shock wave, perhaps from galaxy collisions or group interactions. When galaxies crash together, they release enormous amounts of energy, capable of pushing waves of plasma through intergalactic space. These shock fronts could produce circular shells of radio emission.
Yet the data from this study favors the AGN relic model. The host galaxy, WISEA J035609.67–421603.5, has colors consistent with being an AGN, and the symmetry of the rings points toward jet-driven activity. In the words of the research team: “An AGN-related origin appears to be the more consistent interpretation.”
The Human Side of the Discovery
Beyond the numbers and technical details, discoveries like ORC J0356–4216 touch something deeply human. Imagine gazing through a telescope and seeing not a star, not a galaxy, but a glowing ring of energy two million light-years wide—an echo of a cosmic drama that played out hundreds of millions of years ago. These are not just objects; they are stories, written in the invisible language of radio waves.
Each ORC challenges our imagination, reminding us how little we truly know about the universe. Even in an era when we can map billions of galaxies and detect gravitational waves, the cosmos still surprises us with phenomena so strange they demand entirely new categories. ORCs are a reminder that astronomy is not a finished book, but an unfolding adventure.
Why ORCs Matter
Odd Radio Circles may turn out to be crucial for our understanding of how galaxies evolve. If they are indeed relics of AGN activity, they reveal the lifecycles of supermassive black holes and the massive structures they create in their wake. If they are shock waves from galaxy interactions, they could help explain how cosmic matter and magnetic fields are stirred and spread through intergalactic space.
In either case, they open a new window into the invisible universe—the universe that doesn’t shine in visible light, but instead whispers in radio waves. With next-generation instruments like the Square Kilometre Array (SKA), astronomers may soon uncover many more ORCs, piecing together a broader picture of their origins and meaning.
A Universe Still Full of Surprises
ORC J0356–4216 is more than just an astronomical curiosity. It is a symbol of the unknown, a reminder that the universe is far stranger than our textbooks predict. Every new discovery like this expands the boundaries of human knowledge and deepens our sense of wonder.
We stand on a tiny planet, orbiting an ordinary star, in one corner of one galaxy—and yet, with our instruments, we can glimpse structures millions of light-years across, born from forces beyond comprehension. Physics and astronomy give us the tools to understand, but it is awe that drives us to look up in the first place.
Odd Radio Circles are the cosmos’s way of telling us: there is still so much left to discover. And with ORC J0356–4216, we have taken one more step into the mystery.
More information: Sam Taziaux et al, Deep polarimetry study reveals double ring ORC-like structures, arXiv (2025). DOI: 10.48550/arxiv.2509.04981
