Researchers believe they have discovered a new, bizarre type of cosmic object that is invisible to all wavelengths of light except radio.
The mysterious rings have been dubbed Odd Radio Circles, or ORCs, as they “do not seem to correspond to any known type of object”, according to a recent study published by a team led by Western Sydney University astrophysicist Ray Norris.
All four ORCs are only visible in radio wavelengths. They are completely invisible in X-ray, optical, or infrared wavelengths.
“We have discovered, to the best of our knowledge, a new class of radio-astronomical object, consisting of a circular disc, which in some cases is limb-brightened, and sometimes contains a galaxy at its centre,” the researchers’ study said.
The team’s study has been posted on the preprint server arXiv. It has not yet been peer-reviewed.
Commenting further on the sightings of the ORCs, the scientists added: “None of the known types of radio object seems able to explain it.”
Three of the four ORCs described by the team were detected by the Australian Square Kilometre Array Pathfinder (ASKAP) telescope — a network of radio antennae located in western Australia.
The telescope has been scanning the sky in the radio spectrum as part of efforts to create an Evolutionary Map of the Universe and help scientists better comprehend the development of stars and galaxies.
Norris and his team noticed three ORCs in ASKAP’s 2019 observations, with each of the circles measures about one arcminute in diameter, which is roughly equivalent to 3 per cent the size of the Moon in the night sky.
It remains unclear how far away from Earth they are, which makes it challenging to estimate the actual size of the objects.
The unusual appearance of the glowing circles prompted the researchers to consider whether they might be an instrumental glitch, especially since radio imagery often contains errors that look like rounded apparitions, according to the study.
But later analysis of archival datasets revealed a fourth ORC was imaged in 2013 by India’s Giant Metrewave Radio Telescope.
The fact that the circles show up across multiple telescope datasets makes instrumental error “a very improbable explanation,” the team said in their study.
The team went on to identify several possible identities for the objects, saying they could be the fallout of exploded starts, or “Einstein rings,” which are signatures of warped spacetime created by the gravity of massive objects.
The researchers also mooted the possibility the ORCs could be the ghosts of highly energetic events that occurred millions of years ago – such as gamma ray bursts or plasma jets spewed out by active galactic cores.
“We also acknowledge the possibility that the ORCs may represent more than one phenomenon,” the team noted, adding that they may have been “discovered simultaneously because they match the spatial frequency characteristics of the ASKAP observations, which occupy a part of the observational parameter space which has hitherto been poorly studied.”
Now, the team plan to continue examining the ORCs to see if they can unveil their secrets and sharpen further our view of space.