this second scenario, termed Population III.2 star formation by @tm08, it becomes dominant, cooling the gas down to the temperature of the cosmic microwave background [@no05; @jb06; @yoh07]. The lower gas temperature, plus the higher critical density of HD ($n_{\rm crit} \sim 10^{6} \: {\rm cm^{-3}}$, compared with $n_{\rm crit} \sim 10^{4} \: 
{\rm cm^{-3}}$ for H$_{2}$), means that fragmentation occurs somewhat later, and produces significantly lower mass fragments, with characteristic masses $M \sim 100 \: {\rm M_{\odot}}$. Subsequently, the evolution of these fragments is believed to proceed in the same fashion as described above, resulting ultimately in the formation of a primordial protostar of similar mass. However, since this protostar is embedded in a less massive envelope, with a lower accretion rate, the final stellar mass is thought to be an order of magnitude or so smaller, $M \sim 10 \: {\rm M_{\odot}}$. Nevertheless, this still corresponds to what we would call, by Galactic standards, a massive star, and moreover one which is more than capable of dissociating H$_{2}$ throughout a large volume of the halo, thereby suppressing further star formation.

In the past few years, it has become possible to partially test this picture using numerical simulations that 