More than 99% of the visible universe exists in a superheated state known as plasma—an ionized gas of electrons and ions. The motion of these charged particles produces magnetic fields that form an interstellar magnetic web. These magnetic fields are important for a wide range of processes, from the shaping of galaxies and the formation of stars to controlling the motion and acceleration of high-energy particles like cosmic rays—protons and electrons that zoom through the universe at nearly the speed of light.