On the operation of the chemothermal instability in primordial star-forming clouds

Understand

We investigate the operation of the chemothermal instability in primordial star-forming clouds with a suite of three-dimensional, moving-mesh simulations.

• In line with previous studies, we find that the gas at the centre of high-redshift minihaloes becomes chemothermally unstable as three-body reactions convert the atomic hydrogen into a fully molecular gas.
• The competition between the increasing rate at which the gas cools and the increasing optical depth to H2 line emission creates a characteristic dip in the cooling time over the free-fall time on a scale of 100 au.
• As a result, the free-fall time decreases to below the sound-crossing time, and the cloud may become gravitationally unstable and fragment on a scale of a few tens of au during the initial free-fall phase.