Phase Transition in Spherically Symmetric Gravitational Collapse of a   Massless Scalar Field
  Phase transition in spherically symmetric collapse of a massless scalar field is studied in 4-d Einstein gravity. A class of exact solutions that show the evolution of a constant incoming energy flux turned on at a point in the past null infinity are constructed to serve as an explicit example. The recently discovered phase transition in this system via numerical methods \cite{choptuik} is manifest; above a threshold value of the incooming energy flux, a black hole is dynamically formed and below that, the incoming flux is reflected forward into the future null infinity. The critical exponent is evaluated and discussed using the solutions. 
Youngjai Kiem