  We follow the evolution of the baryonic top-hat overdensity in a single-zone
approximation. Our goal is to juxtapose the evolution of the gas temperature in
the primordial clouds in the lambda cold dark matter model and the warm dark
matter model with keV sterile neutrinos and to check the effects of their
decays, into one X-ray photon and one active neutrino, on the structure
formation. We find that, in all the cases we have examined, the overall effect
of sterile dark matter is to facilitate the cooling of gas and to reduce the
minimal mass of the halo able to collapse. Hence, we conclude that X-rays from
the decays of dark matter in the form of sterile neutrinos can help the early
collapse of gas clouds and the subsequent star formation.
