Compared to the Sun, the star known as GJ 1243 is a dull ember. It’s about a quarter of the Sun’s size and mass, but less than one percent as bright. Yet there’s one way in which it puts the Sun to shame: It produces more of the powerful explosions known as flares, which can be stronger than anything from the Sun. GJ 1243 is a red dwarf. These tiny stars outnumber all the other classes of stars put together. But because they’re the least-massive stars, their light is feeble — not a single one is visible to the unaided eye. Because of its size, though, a red dwarf behaves a little differently from stars like the Sun. All of the gas outside its core is like a big pot of boiling water, with gas circulating between the core and the surface. That generates a powerful magnetic field, which in turn produces big “starspots” — magnetic storms on the star’s surface. The activity also produces flares — powerful outbursts of particles and energy. Astronomers used the planet-hunting Kepler space te
