2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/117593The spherically symmetric perturbations in the spatially flat Friedman models are considered. It is assumed that the Friedmannian density and pressure are related through a linear equation of state. The perturbation is joined smoothly with an unperturbed Friedmann's background at the sound horizon of perturbation. Such junction is in accordance with the "birth" of a local perturbation as a result of the redistribution of matter. The solution of the Einstein's equations is obtained in linear approximation on a Friedmann's background near the the sound horizon of perturbation.iopart, 10 pagesGeneral Relativity and Quantum CosmologyAstrophysicstext