The Sun sometimes produces giant clouds of plasma that try to escape into space. But often they fail: an invisible magnetic cage keeps them near the surface. Such failed eruptions are called "trapped."

Scientists built a computer model to understand exactly how this cage works. It turns out that the external magnetic field, which wraps around the prominence like a rope, doesn't just press down on it from above but also twists it. Powerful electric currents arise, pulling the plasma downward. At the same time, the plasma rotates and rubs against the magnetic field lines of the cage, tearing itself apart.

X-ray observations showed that the hot glow and the radiation from accelerated particles come from different locations. This means that the currents in the cage act like a natural electron accelerator. By the shape of the glowing loops and their tilt, it is now possible to tell in advance whether a plasma cloud will escape into space or remain trapped.