Cooling of Population III objects in a pressure supported collapse

The cooling and collapse of Population III objects is investigated in the framework of ‘flat’ standard cosmological model. It is assumed that the significant component of fluctuations was isothermal and that the cooling of the collapsing cloud was due to the H2 molecule. The pressure inside the cloud is taken into account. The only parameter in these models is the cloud's mass. These numerical solutions show that the first bound systems were of about a million solar masses. In the range of 105−107M⊙ there are four different modes of the behavior of the cloud's radius, depending on the mass: expansion, expansion followed by collapse because of the cooling, collapse after oscillations due to the pressure, and a direct contraction. It is suggested that the different ways to collapse gave rise to different fragmentation processes and hence to different star systems with a similar mass. It is found that the collapse was delayed by the pressure, and the first clouds completed their contraction at redshift 100–140.