Spherically Symmetric Perturbation of Ultrarelativistic Fluid in   Homogeneous and Isotropic Universe
  A solution of the linearized Einstein's equations for a spherically symmetric perturbation of the ultrarelativistic fluid in the homogeneous and isotropic universe is obtained. Conditions on the boundary of the perturbation are discussed. The examples of particle-like and wave-like solutions are given. 
Yu. Ignat'ev, A. Popov (Kazan State Pedagogical University)