The fragmentation of condensations of the primordial gas

We have studied the gravitational collapse of cylindrical condensations of the primordial gas, subject to the virial theorem and in the presence of an initially small, axial magnetic field. Owing to the compression of the magnetic field, the collapse of the cylinder is arrested at larger values of its radius than when the field is neglected. Consequently, the estimates of the masses of the fragments which form are also larger. We find that rotational transitions of HD molecules dominate the cooling of the gas during at least the early phases of the collapse, when the kinetic temperature is low.