We dubbed them ORCs, which stands for "odd radio circles." But the big question, of course, is: "what are they?" At first we suspected an imaging artifact, perhaps generated by a software error. But we soon confirmed they are real, using other radio telescopes. We still have no idea how big or far away they are. They could be objects in our galaxy, perhaps a few light-years across, or they could be far away in the Universe and maybe millions of light years across. When we look in images taken with optical telescopes at the position of ORCs, we see...