Odd radio circles perplex astronomers

Odd radio circles: greenish sphere made of rings with starry background.
This is an ORC (Odd Radio Circle). It’s a circle in space, brighter along its edges, and visible only at radio wavelengths. This image, via J. English/ SARAO, comes from the MeerKAT radio telescope, an array of 64 antennas in the Northern Cape of South Africa. Read more about this image.

Odd radio circles

The South African Radio Astronomy Observatory (SARAO) released a new image yesterday (March 22, 2022) of what it called the astronomy’s newest mystery. It’s the image you see above. Astronomers call it an odd radio circle or ORC. Astronomers have spotted only a handful of ORCs. They’re huge, about a million light-years across (16 times bigger than our Milky Way galaxy). Despite this, the ORCs are hard to see. They’re visible only at radio wavelengths. And, so far, they are unexplained. Since their discovery in 2019, astronomers have proposed different explanations for them, including galactic shockwaves, or the throats of wormholes. What are they?

Ray Norris from Western Sydney University and CSIRO, one of the authors on a new paper about ORCs, said only five odd radio circles have ever been revealed in space. Norris said in an article released March 21, on The Conversation:

We can now see each ORC is centred on a galaxy too faint to be detected earlier. The circles are most likely enormous explosions of hot gas, about a million light years across, emanating from the central galaxy.

But, he added, scientists still don’t know what causes ORCs, or why they are so rare.

As of now, there are three leading theories to explain what causes ORCs:

– They could be the remnant of a huge explosion at the center of their host galaxy, like the merger of two supermassive black holes.
– They could be powerful jets of energetic particles spewing out of a galaxy’s center.
– They might be the result of a starburst “termination shock” from the production of stars in the galaxy.

Jordan Collier of the Inter-University Institute for Data Intensive Astronomy – formed by three South African universities – worked on the data from the MeerKAT radio telescope in South Africa. Collier said:

People often want to explain their observations and show that they align with our best knowledge. To me, it’s much more exciting to discover something new, that defies our current understanding.

MeerKAT is cool

Fernando Camilo – who is chief scientist of the SARAO, which built and operates Meerkat – said that the ORC project “played to MeerKAT’s strengths.” And MeerKAT does have some amazing strengths. It’s produced very interesting results prior to this, unrelated to the ORCs.

Still, these astronomers said that, to really understand odd radio circles they’ll need access to even more sensitive radio telescopes such as those of the SKA Observatory, which is supported by more than a dozen countries all over the world, and which MeerKAT will be a part of.

More cool science from MeerKAT: Shock wave from colliding galaxy clusters spans 60 Milky Ways

Left image blurry version of right image, white background, black dots and nebulous feature at center.
The image of the left is from the ASKAP telescope on Australia, which made the first discovery of the ORC. The new data from the South African telescope MeerKAT (on the right and in the color image at the top of this article) are twice as detailed and measuring more than 10 times as faint levels. Image via SARAO.

Bottom line: The South African Radio Astronomy Observatory released a new image of ORCs on March 22, 2022. ORCs are odd radio circles in space.


Via The Conversation

March 23, 2022

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