New data reveals secrets of million-light-year-wide "odd radio circles"
Astronomers may be a step closer to solving a cosmic mystery known as odd radio circles (ORCs). New images, captured by the MeerKAT radio telescope, are the clearest and most detailed yet taken of an ORC, helping to narrow down the list of suspects as to what creates them.
Like many astronomical anomalies, the name tells you pretty much everything you need to know about odd radio circles – they’re round blobs of radio emissions that can’t be explained by known objects or phenomena. They’re a pretty recent mystery too, with the first only being discovered in September 2019 and a total of just five confirmed so far.
These ghostly rings are tricky to study thanks to their faintness, their rarity, and the fact that they don’t show up in optical, infrared or X-ray wavelengths. Early on, astronomers couldn’t even be sure whether they were huge and far away, or smaller and within our own galaxy.
More recent observations helped to pin down their size and distance, finding that the former was the case – ORCs are about a million light-years wide, making them roughly 16 times bigger than the Milky Way. Intriguingly, they seem to center on galaxies with active supermassive black holes in the core, which could provide clues to their origin.
In the new study, astronomers peered closer at the very first ORC discovered, using the MeerKAT radio telescope in South Africa to capture far more detailed images than ever before. The end results reveal a complex structure containing multiple interior circles, and allowed the team to produce maps of the radiation’s polarization and spectral index.
With all this new data, the researchers were able to propose three main hypotheses about what could be producing odd radio circles. They might be the remains of huge explosions from the galaxy at their center, perhaps caused by two supermassive black holes merging. Or they might be circular jets of energetic particles thrown from the galaxy’s center. Or they could be shock waves from the production of stars in the galaxy.
As with any mystery, gathering more data is key to solving what ORCs are. Radio telescopes like MeerKAT and ASKAP will continue to observe the discovered ORCs and search for more. Things will really kick off when the full Square Kilometer Array (SKA) radio telescope comes online around 2027.
The research was published in the journal Monthly Notices of the Royal Astronomical Society.