Astronomers had a mystery on their hands. No matter where they looked, from inside the Milky Way to distant galaxies, they observed a puzzling glow of infrared light. This faint cosmic light, which presents itself as a series of spikes in the infrared spectrum, had no easily identifiable source. It seemed unrelated to any recognizable cosmic feature, like giant interstellar clouds, star-forming regions, or supernova remnants. It was ubiquitous and a bit baffling.