Pulsational pair instability as an explanation for the most luminous supernovae

Collision course SN 2006gy is an extremely luminous super-nova explosion, perhaps a hundred times more energetic than a typical supernova arising from the collapse of the core of a massive star. Current theories suggest that its progenitor was a star more than 100 times the mass of the Sun. That conclusion is at odds with the supernova's spectrum, which indicates the presence of a hydrogen envelope that would have been lost by a massive star long before the explosion. Two groups now present evidence to support alternative explanations for this supernova, both involving collision. Simon Portegies Zwart and Edward van den Heuvel show that the collision frequency of massive stars in a dense young cluster is sufficient to cause an explosion of the scale of SN 2006gy. And Woosley et al. present a model that explains the brightest supernovae as products of collisions between shells of matter ejected by massive stars made unstable by the production of electron–positron pairs.