Most curiously, it occupies a very narrow band of the radio spectrum: 982 megahertz, specifically, which is a region typically bereft of transmissions from human-made satellites and spacecraft. We don't know of any natural way to compress electromagnetic energy into a single bin in frequency such as this one, Siemion says. Perhaps, he says, some as-yet-unknown exotic quirk of plasma physics could be a natural explanation for the tantalizingly concentrated radio waves. But for the moment, the only source that we know of is technological.