In a simulation, magnetic field lines in some stars form a ring of lines twisted around each other (blue). Field lines protruding through the surface (red) are held together and stabilized by the twisted ring inside. This is illustrated by the schematic sketch (the lower right) and the cut through the star (upper right). The field drifts slowly outward over hundreds of millions of years, then distorts into the shape of the seam on a tennis ball (lower left), after which it disappears from the star.
