A spherical Lagrangian hydrodynamical code has been written to study the formation of cosmological structures in the early Universe .
In this code we take into account the presence of collisionless non-baryonic cold dark matter ( CDM ) , the cosmological constant and a series of physical processes present during and after the recombination era , such as photon drag resulting from the cosmic background radiation and hydrogen molecular production .
We follow the evolution of the structure since the recombination era until the present epoch .
As an application of this code we study the formation of voids starting from negative density perturbations which evolved during and after the recombination era .
We analyse a set of COBE -normalized models , using different spectra to see their influence on the formation of voids .
Our results show that large voids with diameters ranging from 10 h ^ { -1 } { Mpc } up to 50 h ^ { -1 } { Mpc } can be formed in a universe model dominated by the cosmological constant ( \Omega _ { \Lambda } \sim 0.8 ) .
This particular scenario is capable of forming large and deep empty regions ( with density contrasts \bar { \delta } < -0.6 ) .
Our results also show that the physical processes acting on the baryonic matter produce a transition region where the radius of the dark matter component is greater than the baryonic void radius .
The thickness of this transition region ranges from about tens of kiloparsecs up to a few megaparsecs , depending on the spectrum considered .
Putative objects formed near voids and within the transition region would have a different amount of baryonic/dark matter when compared with \Omega _ { b } / \Omega _ { d } .
If one were to use these galaxies to determine , by dynamical effects or other techniques , the quantity of dark matter present in the Universe , the result obtained would be only local and not representative of the Universe as a whole .