Warm dark matter is consistent with the observations of the large-scale <br />
structure, and it can also explain the cored density profiles on smaller <br />
scales. However, it has been argued that warm dark matter could delay <br />
the star formation. This does not happen if warm dark matter is made up <br />
of keV sterile neutrinos, which can decay into X-ray photons and active <br />
neutrinos. The X-ray photons have a catalytic effect on the formation of <br />
molecular hydrogen, the essential cooling ingredient in the primordial <br />
gas. In all the cases we have examined, the overall effect of sterile <br />
dark matter is to facilitate the cooling of the gas and to reduce the <br />
minimal mass of the halo prone to collapse. We find that the X-rays from <br />
the decay of keV sterile neutrinos facilitate the collapse of the gas <br />
clouds and the subsequent star formation at high redshift.