A model for ultrarelativistic spherically symmetric Pre-Hawking   radiating gravitational collapse
  In this paper we present a simple but non-simplistic model of gravitational collapse with thermal emission of pre-Hawking radiation. We apply Einstein equations to a time-dependant spherically symmetric metric and an ultrarelativistic stress-energy tensor. In our model, particles either radially approach the center of the star as collapsing matter, or radially flee from it. 
Miquel Pinyol Ribas
gr-qc