Astrophysicists finally have an explanation for the violent mood swings of some of the biggest, brightest and rarest stars in the universe. 3D simulations carried out at the ALCF by a team of astrophysicists suggest that turbulent motion in the outer layers of a massive star creates dense clumps of stellar material. These clumps catch the star’s intense light like a solar sail, erupting material into space. After jettisoning enough mass, the star calms down until its outer layers re-form and the cycle begins anew, the astrophysicists report online September 26 in Nature.