Skip to main content

What Are Odd Radio Circles or ORCs?

Leonard Kelley holds a bachelor's in physics with a minor in mathematics. He loves the academic world and strives to constantly explore it.

Diverting your attention from astronomy for even a moment can cause you to miss new mysteries being uncovered. Sometimes they are hidden in the data and only emerge when processed out. But then there are those that are just simply things seen for the first time and whose cause is unknown. One of the newest members of this class are the odd radio circles, or ORCS. What do we know about these objects and where do they fit into out stellar models?


The first ORCs spotted were by Ray Norris (Western Sydney University in Australia) and his team using the Australian Square Kilometer Array Pathfinder, or ASKAP, during a survey identifying all known celestial radio sources. During this pilot survey for the Evolutionary Map of the Universe from July 2019 to November 2019, 3 strange objects only visible in the radio spectrum were seen.

All were ring-like, roughly symmetrical and also very faint and therefore hard to see. Another ORC was found in archival data of Abell 2142 from the Giant MetreWave Radio Telescope or GMRT (Murugesu, Norris, N. Anderson, P. Anderson, Groh, Starr).

ORC 1 with a potentially related orange galaxy in the center.

ORC 1 with a potentially related orange galaxy in the center.


What do we know about these ORCs? Well, two of the initial four seem to have a galaxy in their center while the other two don’t. It is unclear if there is a causal relationship between those galaxies and the ORCs. Three of the ORCs are partial rings while ORC 3 seems to be a uniform disc. This could imply that they are spherical in nature and that depending on their strength we can only see their edges defined well.

They are all high above our galactic plane and average about 1 arc minute in apparent size, hinting at an extragalactic origin. 2 of the ORCs seem to be close by, possibly hinting at a common origin. Because of a lack of context with regard to a host object we do not know the distances to these objects. If ORC 4’s central galaxy truly is tied to it, then that ORC would be 4.2 billion light-years away and have 1.1 by 0.9 million light-year dimensions (Murugesu, Norris, N. Anderson, P. Anderson, Groh, Starr).

Several ORCs spotted.

Several ORCs spotted.

What They Are Not

With so little to work off of, can we eliminate any options? Absolutely. We know they are not a technological hiccup, for many radio telescopes have spotted these objects. They are not supernova remnants despite a similar appearance, but they don’t match any of the properties of them and also lack the necessary population (for if a type of remnant, should by only 350 seen in Milky Way, but based on where we have seen ORCs, would be more like 50,000).

They are not from gravitational lensing because no massive objects exist between us and them to distort their spectrums. They are not ring galaxies because of their radio-only spectrum despite ring galaxies being visible (Murugesu, Norris, P. Anderson, Groh, Starr, Irving).

What They Could Be

This doesn’t leave us with much options, but don’t be discouraged. These ORCs could possibly be some type of emanation from a radio galaxy, or possible a shockwave from some extragalactic event. If so, then based on the angular size it would have happened a long time ago.

ORCs could be tied to currently known transient events such as fast radio bursts (FRBs), gamma ray bursts (GRBs), neutron star collisions or possibly even black hole mergers, but this is all strictly theoretical (Norris, N. Anderson, P. Anderson, Groh, Starr, Irving).

It could even be something else, something brand new never before encountered. Of course, it’s most likely a simple explanation, but who knows…

Works Cited

Anderson, Natali. “New Class of Radio-Astronomical Objects Discovered: Odd Radio Circles.”, 13 Jul. 2020. Web. 18 Mar. 2021.

Anderson, Paul Scott. “Astronomers ponder Odd Radio Circles in space.” EarthSky Communications Inc., 24 Jul. 2020. Web. 18 Mar. 2021.

Groh, Mara Johnson. “4 mysterious objects spotted in deep space are unlike anything ever seen.” Future US Inc, 08 Jul. 2020. Web. 18 Mar. 2021.

Irving, Michael. “’Odd radio circles’ are the latest cosmic mystery to stump astronomers.” New Atlas, 02 Dec. 2020. Web. 18 Mar. 2021.

Murugesu, Jason Arunn. “Circles in space are like nothing we’ve ever seen.” New Scientist. New Scientist Ltd., 11 Jul. 2020. Print. 14.

Norris, Ray. “’Newly discovered ghostly circles in the sky can’t be explained by current theories, and astronomers are excited.” The Conversation US, Inc, 01 Dec. 2020. Web. 18 Mar. 2021.

Starr, Michelle. “Astronomers Detect Unexpected Class of Mysterious Circular Objects in Space. Science Alert, 09 Jul. 2020. Web. 18 Mar. 2021.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2022 Leonard Kelley