Mysterious circles of radio waves found in space have left astronomers scratching their heads, with no idea how they formed, or even how big or far away they are. They don鈥檛 seem to match anything that has been seen in space before, so researchers have dubbed them Odd Radio Circles, or ORCs.
Ray Norris at Western Sydney University, Australia, and his colleagues found these unexplained objects using the Australian Square Kilometre Array Pathfinder (ASKAP) telescope, which was completed in 2018. The discovery was made as part of a project aiming to take a census of all the radio sources in the sky.
The researchers discovered four of the circles in total: three using ASKAP and another when searching through archival data from a different telescope. The team suggests that previous surveys had failed to observe these circles as their telescopes were unable to detect such faint radio waves.
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鈥淲henever we have new search capabilities that come online, we can expect to discover the unexpected,鈥� says Jason Wright at Pennsylvania State University.
We know very little about the ORCs at present. They are symmetrical and their edges are brighter than their interior. Two of them have a galaxy in the middle, while the other two don鈥檛.
We don鈥檛 even know how big or far away they are, as the team was unable to associate them with objects of a known distance. Two appear close together in the sky, but their physical distance from each other is unknown.
It isn鈥檛 clear if all four objects have a similar origin, and so far the researchers have no explanation for what they are, although they were able to confirm that the objects aren鈥檛 just artefacts of the ASKAP telescope by observing them through other instruments.
鈥淚 think this paper does a really good job of running through all the possibilities of what they could be, or at least everything they can think of 鈥� including whether they鈥檙e not real,鈥� says Wright.
The team says that ORCs most closely resemble supernova remnants, the material and energy released when a star explodes. But Mikako Matsuura at Cardiff University, UK, says that is unlikely.
鈥淲e know how many stars there are, due to past radio surveys, so we know approximately how many remnants from star explosions should be found too, 鈥� she says. The researchers note that there are only 350 confirmed supernova remnants in the galaxy and the likelihood of finding three of them in the ASKAP survey is 0.02 per cent.
Another explanation is that they are simply galaxies in the shape of a circle, known as ring galaxies. Such galaxies are usually easy to observe with optical telescopes, but the ORCs only appear in radio.
One possibility the team didn鈥檛 consider is whether the ORCs could be caused by aliens 鈥� but Wright says that is unlikely. 鈥淚 can鈥檛 think of any reason.鈥�
To figure out what these objects are, we need to discover more of them, says Wright. 鈥淚f these findings are as interesting as they seem to be, then people will use other telescope arrays to go looking for them,鈥� he says, or look for more in archival data. 鈥淥nce you have a lot of them, you can then start collecting clues.鈥�
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