'Odd' Circles of Radio Waves Coming from Unknown Cosmic Source Discovered

Strange, never-before-seen circles of radio waves have been discovered in space. Researchers in Australia say what is producing the "odd radio circles"—or ORCs—is unknown.

The team, led by Ray Norris, Professor of Applied Data Science In Astrophysics at the Western Sydney University, found the ORCs while they were carrying out a survey of the universe using the Australian Square Kilometre Array Pathfinder telescope (ASKAP).

The team initially found three ORCs by visually inspecting images taken during the survey. A fourth was found in archival data taken in March 2013, they wrote in a preprint study appearing on the arXiv.org website. The research has been submitted to the journal Nature Astronomy, but has not yet been peer reviewed by a group of experts, so findings should be taken with a degree of caution.

Researchers say circular features are common in radio images from space. They normally show spherical objects such as supernova remnants and protoplanetary discs. However, the ORCs they found do not fit with any known source, "but rather appear to be a new class of astronomical object."

"None of the ORCs has obvious optical, infrared, or X-ray counterparts to the diffuse emission, although in two cases there is an optical galaxy near the centre of the radio emission." the team wrote. They said the circular objects appear in radio images as brightened disks. All ORCs had "strong circular symmetry" and all had a diameter of around one archmin. This is a unit of angular measurement and corresponds to one sixtieth of a degree of an angle.

The team looked at several explanations for the objects, assuming all had a similar source. They found the ORCs were highly unlikely to be a result of imaging issues as two of the objects were identified by different telescopes at different times. They also rule out the objects being the result of a supernova remnant—the structure left over after the explosion of a star—galactic planetary nebula, objects that form at the end of the lives of certain stars. Several other potential sources are also considered to be unlikely

Instead, the researchers say the ORCs may be the result of a spherical shock wave from galactic winds. "While this is a theoretical possibility, such a shock has not yet been observed elsewhere," they say. Another possibility is they represent an "outflow, or a remnant, from a radio galaxy viewed end-on."

"It is also possible that the ORCs represent a new category of a known phenomenon, such as the jets of a radio galaxy or blazar when seen end-on, down the 'barrel' of the jet," the team wrote. "Alternatively, they may represent some remnant of a previous outflow from a radio galaxy. However, no existing observations of this phenomenon closely resemble the ORCs in features such as the edge-brightening or the absence of a visual blazar or radio galaxy at the centre."

They said more work is needed to investigate the source of these mystery objects.

Kaustubh Rajwade, from the Jodrell Bank Centre for Astrophysics, University of Manchester, U.K., who was not involved in the study, said the paper represents an "intriguing discovery."

"The fact that these 'ORCs' have been observed with different telescopes at different times rules out spurious artefacts as their origins," he told Newsweek. "The radio morphology immediately reminds me of supernova remnants or planetary nebulae but as the authors suggest, finding so many of them in such a small volume off the Galactic Plane seems unlikely.

"I think the prospect of them being relics of an older explosion is really exciting. Such events can produce a spherical shock wave that can light up the ambient medium. The only way to know more about these mysterious objects is through deep observations at multiple wavelengths."

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Stock image representing a galaxy. Researchers have found strange circles of radio emissions in space, the source of which is unknown. iStock