Revealing the invisible: Detecting variations in extragalactic magnetic fields

Magnetic fields are common throughout the universe but incredibly challenging to study. They don't directly emit or reflect light, and light from all along the electromagnetic spectrum remains the primary purveyor of astrophysical data. Instead, researchers have had to find the equivalent of cosmic iron filings--matter in galaxies that is sensitive to magnetic fields and also emits light marked by the fields' structure and intensity.