Scientists have spotted a new kind of signal in space- four strange, circular objects. Three are particularly bright around their edges, like rings, or bubbles. And they have no idea what they are.
Astrophysicist Ray Norris form Western Sydney University in Australia, and his international team of astronomers have called them 'ORCs'- or 'Odd Radio Circles'. They were first spotted in data from the late 2019 Pilot Survey of the Evolutionary Map of the Universe using the Australian Square Kilometre Array Pathfinder, one of the most sensitive radio telescopes in the world.
In the paper, the researchers explain how circular features are common in radio astronomical images. They can represent many things- from the remnants of a supernova, planetary nebulas, circumstellar shells, to a star-forming galaxy. Sometimes though, they are also signaling errors.
Although they initially thought that their findings came from faulty readings, the discovery of a fourth ORC, from archival data collected in 2013, put those suspicion to rest.
As the astronomers say they can not identify the circles, they speculate that they may be a 'new class of astronomical object.'
Further observations revealed that all four ORCs are at high galactic latitudes and are approximately one arcminute in diameter. In layman terms, that equals about 3% the size of the Moon in the night sky. However, as we don't know their distance from Earth, how big they really are remains unknown.
The team currently believes that whatever caused the ORCs lies outside of the Milky Way- perhaps a giant spherical shock wave from an event beyond our galaxy.
"Several such classes of transient events, capable of producing a spherical shock wave, have recently been discovered, such as fast radio bursts, gamma-ray bursts, and neutron star mergers. However, because of the large angular size of the ORCs, any such transients would have taken place in the distant past," write the researchers in their study.
"It is also possible that the ORCs represent a new category of a known phenomenon, such as the jets of a radio galaxy or blazar when seen end-on, down the 'barrel' of the jet. Alternatively, they may represent some remnant of a previous outflow from a radio galaxy."
Sources: Science Alert, arXiv