Strangely sharp circles of radio waves in space have puzzled astronomers since their surprise discovery in 2019. Now, a team has analyzed one closely in hopes that it might give up its secrets.
Firing up a new observatory brings the possibility of discovering brand-new phenomena out in space that our technology has not been able to see before.
That’s precisely what happened in 2019, when the first pilot survey of CSIRO’s ASKAP radio telescope spotted several odd radio circles. They were named, in classic astronomer fashion, “odd radio circles” (ORCs).
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These huge, bright, eerily circular structures are clearly visible in radio wavelengths but are invisible in optical, infrared, or X-ray wavelengths. Only about 10 candidates are known so far, and their origin remains unexplained.
For the new study, a team led by scientists at Ruhr University Bochum in Germany closely examined one such circle, designated ORC J0356-4216.
The team used the ASKAP and MeerKAT radio telescopes – the latter of which originally discovered the ORC in October 2023 – to study the wavelengths and polarization of J0356-4216’s radio waves.
The astronomers discovered that the ORC is made up of two symmetrical rings, spanning a total diameter of about 2.18 million light-years. They seem to have a polarization of between 20 and 30 percent, with a magnetic field oriented tangentially to the rings.
Like many other ORCs, J0356-4216 is centered on a galaxy, and that could be key to figuring out how they form.
frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>The researchers say that the most likely explanation is that it’s a shock wave from past activity in the galaxy, which could include starburst outflows, a collision between two galaxies, or a phase when the central supermassive black hole flared up with increased activity as an active galactic nucleus (AGN).
“In the case of ORC J0356–4216, the observed double-lobed morphology and polarization characteristics are more readily explained by relic emission from previous AGN activity or jet-driven outflows,” the researchers conclude.
The research has yet to be peer-reviewed, but is available as a preprint on the arXiv server.