For decades, astronomers have puzzled over the exact source of a peculiar type of faint microwave light emanating from a number of regions across the Milky Way. Known as anomalous microwave emission (AME), this light comes from energy released by rapidly spinning nanoparticles—bits of matter so small that they defy detection by ordinary microscopes. (The period on an average printed page is approximately 500,000 nanometers across.)