Critical Behavior in Gravitational Collapse of a Yang-Mills Field

We present results from a numerical study of spherically symmetric collapse of a self-gravitating, SU(2) gauge field. Two distinct critical solutions are observed at the threshold of black hole formation. In one case, the critical solution is discretely self-similar, and black holes of arbitrarily small mass can form. However, in the other instance, the critical solution is the n  =  1 static Bartnik-Mckinnon sphaleron, and black hole formation turns on at finite mass. The transition between these two scenarios is characterized by the superposition of both types of critical behavior.