Gamma ray burst formation. Image 1 of 5. Computer artwork of a Wolf-Rayet star just before its core collapses during a gamma ray burst (GRB) event. Wolf-Rayet stars, large, hot blue stars of 10-15 solar masses, shed their outer layers, forming a nebula. The collapse of the core of a massive star like this is now thought to account for GRBs. This collapsar theory says a black hole forms when the core collapses, and its spin or its magnetic field forms ejected material into jets. The jets are the source of the gamma rays of the GRB, a massive short-lived burst of energy that is hundreds of times brighter than an ordinary supernova. For the formation of a GRB, see images R670/148-152.