Radiation in the process of the formation of voids

Abstract

This paper aims to investigate the influence of inhomogeneous radiation in void formation. Since the process of void formation is non-linear, a fully relativistic model, which simulates the evolution of voids from the moment of the last scattering until the present instant, is presented. It is found that in order to obtain a model of a void which evolves from δ0=−10−5 at the last scattering moment to the present day δ=−0.94, the existence of radiation must be taken into account. The ratio of radiation energy density to matter energy density in cold dark matter (CDM) models at the moment of last scattering is 1/5. This paper proves that such a value of radiation energy density cannot be neglected and influences the first stages of void evolution. Namely, it is important to the process of structure formation and hence significantly influences the dynamics of the Universe in the first millions of years after the last scattering. From the fact that the evolution of voids proceeds differently in various cosmological background models, we use the process of void formation to put some limits on values of cosmological parameters. We find that the model with Ωmat∼ 0.3 fits the observational data best.