The Australian Square Kilometer Array Pathfinder was used to scan the skies for radio waves.

There's something unusual lurking out in the depths of space: Astronomers have discovered four faint objects that at radio wavelengths are highly circular and brighter along their edges. And they're unlike any class of astronomical object ever seen before. 

The objects, which look like distant ring-shaped islands, have been dubbed odd radio circles, or ORCs, for their shape and overall peculiarity. Astronomers don't yet know exactly how far away these ORCs are, but they could be linked to distant galaxies. All objects were found away from the Milky Way's galactic plane and are around 1 arcminute across (for comparison, the moon's diameter is 31 arcminutes). 

In a new paper detailing the discovery, the astronomers offer several possible explanations, but none quite fits the bill for all four new ORCs. After ruling out objects like supernovas, star-forming galaxies, planetary nebulas and gravitational lensing — a magnifying effect due to the bending of space-time by nearby massive objects — among other things, the astronomers speculate that the objects could be shockwaves leftover from some extragalactic event or possibly activity from a radio galaxy.