Odd radio circle

In astronomy, an odd radio circle (ORC) is a very large (over 50 thousand times the diameter of our Milky Way ~ 3 million light years) unexplained astronomical object that, at radio wavelengths, is highly circular and brighter along its edges.

[5][10] The ORCs were detected in late 2019 after astronomer Anna Kapinska studied a Pilot Survey of the Evolutionary Map of the Universe (EMU), based on the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope array.

The possibility of a spherical shock wave, associated with fast radio bursts, gamma-ray bursts, or neutron star mergers, was considered, but, if related, would have to have taken place in the distant past due to the large angular size of the ORCs, according to the researchers.

[7] Also, according to the astronomers, "Circular features are well-known in radio astronomical images, and usually represent a spherical object such as a supernova remnant, a planetary nebula, a circumstellar shell, or a face-on disc such as a protoplanetary disc or a star-forming galaxy, ...

They may also arise from imaging artefact around bright sources caused by calibration errors or inadequate deconvolution.

Image of Odd radio circle ORC J2103-6200 by the MeerKAT telescope superimposed on an optical image from the Dark Energy Survey (2022) [ 1 ] [ 2 ]
Artist’s impression of an odd radio circle exploding from a central galaxy. ORCs can expand past other galaxies. [ 1 ] [ 2 ]
Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope array