  Among many physical processes involved in star formation, radiation transfer
is one of the key processes since it dominantly controls the thermodynamics.
Because metallicities control opacities, they are one of the important
environmental parameters which affect star formation processes. In this work, I
investigate protostellar collapse in solar-metallicity and low-metallicity ($Z
= 0.1 Z_\odot$) environments using 3D radiation hydrodynamic and
magnetohydrodynamic simulations. Because radiation cooling is more effective in
the low-metallicity environments, first cores are colder and have lower
entropies. As a result, first cores are smaller, less massive and have shorter
lifetimes in the low-metallicity clouds. Therefore, first cores would be less
likely to be found in low-metallicity star forming clouds. This also implies
that first cores tend to be more gravitationally unstable and susceptible to
fragmentation. The evolution and structure of protostellar cores formed after
the second collapse weakly depend on metallicities in the spherical and
magnetized models despite the large difference in the metallicities. Because
this is due to the change of the heat capacity by dissociation and ionization
of hydrogen, it is a general consequence of the second collapse as long as the
effects of radiation cooling are not very large during the second collapse. On
the other hand, the effects of different metallicities are more significant in
the rotating models without magnetic fields, because they evolve slower than
other models and therefore more affected by radiation cooling.
