Scientists Discover Giant Radio Rings That Could Reveal How Galaxies Sculpt Cosmic Plasma

RAD@home volunteers have found three rare, ringlike radio sources in deep low-frequency surveys, including the most distant and most powerful Odd Radio Circle yet, offering new clues about how jets, winds, and environments shape galaxies at enormous scales. These discoveries show that human pattern recognition still finds surprises that automated pipelines miss, and they point to specific observations that can test competing formation scenarios.

A citizen-science team, RAD@home, inspected LoTSS and TGSS maps and identified three striking ring-shaped radio sources: a twin, intersecting Odd Radio Circle at photometric redshift z ≈ 0.94, a 100 kpc limb-brightened ring formed when a giant radio galaxy’s jet is deflected, and a ring produced where a filamentary jet meets a neighboring galaxy or wind. These systems offer direct, observable tests of relic synchrotron shells, backflow vortices, and jet–galaxy interactions.

Giant bubbles in empty space, and why they matter

If you picture a soap bubble in a garden, then imagine that bubble scaled to the size of a galaxy cluster, glowing in radio light instead of reflecting sunlight. That evocative image captures part of the mystery revealed by recent deep radio surveys: faint, roughly circular shells of synchrotron emission that surround otherwise ordinary galaxies, yet do not fit classical radio jet morphologies. These objects, known as Odd Radio Circles or ORCs, are rare, large, and often spectrally steep, which means their radio light is dominated by aged cosmic-ray electrons rather than ongoing jet activity. The RAD@home collaboratory has added three new and striking members to this small family of sources, widening the range of ring morphologies astronomers must explain.

Understanding these rings matters because they trace the interaction of relativistic plasma, magnetic fields, and ambient gas across hundreds of thousands of light years. Those interactions are the same ones that regulate how active galactic nuclei deposit energy into their surroundings, and how galaxies and clusters evolve over cosmic time. The new RAD@home discoveries therefore provide fresh, concrete targets for testing models of galaxy feedback, shock revival of relic plasma, and jet–environment dynamics.

The problem: where do radio rings come from?

ORCs and ring-shaped radio structures pose a simple but pressing question: what physical process can produce a near-circular, large-scale shell of synchrotron emission that is not clearly a classical lobe, hotspot, or supernova remnant? Observations to date show consistent traits: low surface brightness, steep radio spectra, sizes from a few tens to several hundreds of kiloparsecs, and in many cases a galaxy near the center that is plausibly the host. These properties rule out ordinary Galactic sources and point toward an extragalactic origin, but multiple scenarios can produce ringlike synchrotron features. Candidate ideas include shock-revived fossil lobes, buoyant backflow bubbles that roll into toruses, large bipolar superwinds from host galaxies, and jet impacts on companion galaxies that create bow-shock and ring morphologies. Distinguishing between these options requires well measured sizes, spectral aging, polarization, and the larger environmental context.

The approach: human eyes, multi-survey maps, and citizen science

RAD@home used a human-centric workflow to spot unusual morphologies in public low-frequency radio surveys. Trained volunteers overlay radio contours from LoTSS DR2 and TGSS onto optical and infrared images, examine low and high resolution maps, and discuss candidates with professional mentors. This visual inspection is complemented by cross checks in NVSS, VLASS, and LoLSS maps to obtain measurements across frequency and angular scale. The team also applies simple image processing, such as Sobel filtering, to emphasize sharp brightness gradients and filamentary structures. Because ring sources are rare and extended, they often evade automated classifiers that were trained on more typical morphologies. The RAD@home pipeline thus combines human pattern recognition with multiwavelength vetting to produce a short list of high-value targets for follow up.

The breakthrough discoveries

RAD@home reports three systems that exemplify different formation pathways for ringlike radio structures. Each system sits in a group or cluster scale halo (mass ∼10^14 M⊙), suggesting that the environment is an important piece of the puzzle. Below I summarize the observational highlights and the physical interpretations the scientists propose.

RAD J131346.9+500320 — a twin, intersecting Odd Radio Circle at zphot ≈ 0.94

The most striking source is RAD J131346.9+500320, the first clear ORC found in LoTSS and, at photometric redshift zphot = 0.937 ± 0.045, the most distant ORC reported so far. It exhibits two intersecting, roughly circular rings each about 300 kpc across, embedded in diffuse radio emission that spans roughly 800 kpc in projection. The integrated 144 MHz flux density of the ring plus diffuse emission is 43.2 ± 4.1 mJy, and combined low-frequency measurements give a steep spectral index (α144 54 = 1.22 ± 0.15), consistent with aged, relic synchrotron plasma rather than freshly accelerated jet emission. The radio luminosity at 144 MHz is estimated at 2.27 × 10^26 W Hz−1, nearly two orders of magnitude more luminous than previously known ORCs. These properties position this object as both unusually luminous and unusually distant among the ORC population.

The geometry of two intersecting rings raises immediate geometric questions about three-dimensional shape and viewing angle. If the structures are hollow shells or spheres, intermediate inclinations can naturally produce intersecting circles on the sky. The scientists note the presence of many galaxies at similar redshift in the field, implying a group or poor cluster that could provide a medium for a large scale shock or wind to compress and light up fossil radio plasma. One speculative scenario the scientists discuss is a bipolar superwind interacting with relic lobes from earlier radio activity, producing twin rings that expand along the galaxy’s major axis. This twin-ring geometry may be easier to form if the host is a "Speca-like" optical disk galaxy that can drive bipolar outflows while also hosting extended radio relics.

RAD J122622.6+640622 — a giant radio galaxy with a diverted backflow ring

RAD J122622.6+640622 is a giant radio galaxy extending roughly 865 kpc in projection, whose southern jet undergoes a sharp deflection at a reflection knot roughly 100 kpc from the core. Beyond that knot the plasma flows westward and inflates a limb-brightened ring about 100 kpc in diameter. The host is spectroscopically confirmed at zspec = 0.11024, and the source sits near the edge of a cluster virial radius, where the intra-cluster medium can present abrupt pressure gradients. The integrated 144 MHz flux density measured from LoTSS is 660 ± 70 mJy, corresponding to a radio power near 2 × 10^25 W Hz−1. The scientists draw an analogy with NGC 7016 where backflow plasma expands into an X-ray cavity and rolls into a torus; a similar buoyant backflow vortex or a backflow constrained by a sharp pressure boundary can produce the observed ring in RAD J122622.6+640622.

Three formation mechanisms are offered as plausible for this system, none of which can yet be decisively chosen: a direct jet deflection by a dense obstacle or steep ICM pressure gradient, a buoyant backflow vortex at the cluster’s virial boundary, or asymmetric environment that allows one jet to propagate freely while the other is deflected and curls into a ring. Further polarization and X-ray imaging can distinguish these scenarios.

RAD J142004.0+621715 — a ring at the end of a filamentary jet, possibly from jet–galaxy interaction

The third system, RAD J142004.0+621715, is a filamentary radio galaxy hosted by the brightest cluster galaxy of a massive cluster (M500 ≈ 1.63 × 10^14 M⊙). A loose filamentary jet extends north for roughly 120 kpc, then broadens into a limb-brightened ring about 64 kpc by 47 kpc. The host is at zspec = 0.14140, and the integrated 144 MHz flux density for the whole source is 104.2 ± 10 mJy, with the ring contributing about 31.5 ± 3 mJy. A red, edge-on disc galaxy sits on the western side of the ring and shows an extraplanar red finger of ionized gas, which suggests ram-pressure stripping or a galactic superwind. The scientists discuss a magnetospheric analogue, where a galactic wind compresses and deflects impinging plasma, creating a limb-brightened ring on the windward side and a downstream tail on the leeward side. Alternatively, a jet striking the interstellar medium of the companion galaxy may produce localized reacceleration and ring formation. Either way, this example underscores how jet–galaxy encounters in dense environments can generate ringlike morphologies distinct from classical lobes.

Why these discoveries matter: physics, feedback, and the limits of automation

Three immediate scientific gains flow from RAD@home’s findings.

First, the new systems expand the observational parameter space of ringlike synchrotron structures, from a few 10s of kiloparsecs up to nearly a megaparsec, and from modest radio luminosities to the exceptionally luminous ORC at z ≈ 0.94. That range constrains models: any successful mechanism must operate across wide spatial and energetic scales.

Second, the morphologies link directly to physical processes. Deflected jets and redirected backflows map where the surrounding medium has steep gradients or obstacles; buoyant vortices reveal cavities and the dynamics of bubble rise in cluster gas; and jet–galaxy impacts map sites of local reacceleration and gas stripping. Each ring is therefore a diagnostic of the interplay between relativistic plasma and thermal gas. Targeted polarization and rotation measure imaging, coupled to X-ray observations that can reveal cavities and pressure structure, will let astronomers discriminate among hypotheses and recover the energetics and ages of these features.

Third, on the methodological side, these discoveries illustrate the complementarity of human and machine classification. Large surveys produce millions of sources, and automated pipelines are indispensable for scale, but rare morphologies are poorly represented in training sets. Human volunteers, when carefully trained, can flag the unexpected and supply examples that improve machine learning. The RAD@home work underscores the value of citizen science, both for discovery and for building the training catalogs that more robustly capture the diversity of extragalactic radio morphologies.

Caveats and next steps

The paper is careful about limitations, which is the right approach when dealing with rare, extended sources. For the ORC, the host redshift is photometric rather than spectroscopic, which introduces uncertainty in the physical size and luminosity estimates. For the ring in the giant radio galaxy, NVSS resolution prevents clean separation of flux components, so spectral aging was not computed for the ring. In all three cases, the most decisive diagnostics are still missing: sensitive polarization and rotation measure maps to reveal magnetic field geometry, multifrequency radio imaging to constrain electron aging and spectral curvature, and deep X-ray data to search for co-spatial cavities or shocks. The scientists explicitly call for follow up with LOFAR, JVLA, GMRT, and X-ray facilities to settle which processes are at work in each system. Those observations will allow the community to move from plausible scenarios to falsified or supported models.

Conclusion: rings as laboratories, and the continuing role of human insight

RAD@home’s three discoveries make a clear, modest claim: ringlike radio structures are more diverse, and occur in more environments, than we appreciated. One of the new objects is an unusually powerful, distant ORC that challenges energy budgets; another shows a clear example of jet deflection that can produce a limb-brightened ring; the third demonstrates how filamentary jets interacting with a neighbor or wind can create compact rings and tails. Together, they turn rings from curiosities into practical laboratories for studying jet dynamics, plasma aging, and galaxy feedback across cosmic scales.

Finally, these results reaffirm a broader lesson for modern astronomy: in an era of petabyte surveys and powerful algorithms, there remains a critical role for trained human pattern recognition. Citizen scientists not only discover oddities, they supply the atypical examples that make automated methods more complete and more creative. The promising next step is a close partnership: humans to flag novelty, instruments to measure diagnostics, and machines to scale the learned patterns across the sky.

The research was published in Monthly Notices of the Royal Astronomical Society on October 02, 2025.