Radiation and String Atmosphere for Relativistic Stars
  We extend the Vaidya radiating metric to include both a radiation field and a string fluid. Assuming diffusive transport for the string fluid, we find new analytic solutions of Einstein's field equations. Our new solutions represent an extention of Xanthopoulos superposition. 
E.N. Glass and J.P. Krisch (Department of Physics, University of   Michigan, Ann Arbor, MI)