An ultrapowerful supernova discovered in 2006 may blow its top again. Burning 100 times brighter than a typical supernova, SN 2006gy maintained full strength for an amazing three months. To explain the massive outburst, researchers invoked a mechanism called pair instability, in which high-energy gamma rays inside the star convert into pairs of electrons and positrons, draining stellar energy that would normally help maintain its internal pressure. That sapping leads to a premature collapse, liberating vast amounts of energy and light. Astrophysicists now report that SN 2006gy's brightness changes fit a model of pulsating pair instability. In this scenario, the initial implosion of a 110-solar-mass star would shed several suns' worth of mass before igniting the star's carbon and oxygen fuel, temporarily halting the collapse. Roughly seven years later pair instability would cause a second breakdown that would emit a smaller but faster pulse of material. The study appears in the November 15, 2007, Nature.