  We present here studies of collapse of purely baryonic Population III objects
with masses ranging from $10M_\odot$ to $10^6M_\odot$. A spherical Lagrangian
hydrodynamic code has been written to study the formation and evolution of the
primordial clouds, from the beginning of the recombination era ($z_{rec} \sim
1500$) until the redshift when the collapse occurs. All the relevant processes
are included in the calculations, as well as, the expansion of the Universe. As
initial condition we take different values for the Hubble constant and for the
baryonic density parameter (considering however a purely baryonic Universe), as
well as different density perturbation spectra, in order to see their influence
on the behavior of the Population III objects evolution. We find, for example,
that the first mass that collapses is $8.5\times10^4M_\odot$ for $h=1$,
$\Omega=0.1$ and $\delta_i={\delta\rho / \rho}=(M /
M_o)^{-1/3}(1+z_{rec})^{-1}$ with the mass scale $M_o=10^{15}M_\odot$. For
$M_o=4\times10^{17}M_\odot$ we obtain $4.4\times10^{4}M_\odot$ for the first
mass that collapses. The cooling-heating and photon drag processes have a key
role in the collapse of the clouds and in their thermal history. Our results
show, for example, that when we disregard the Compton cooling-heating, the
collapse of the objects with masses $>8.5\times10^4M_\odot$ occurs earlier. On
the other hand, disregarding the photon drag process, the collapse occurs at a
higher redshift.

Astrophysics