The first stars formed from primordial gas, formed in the
Big Bang, composed primarily of hydrogen and helium.
It is generally thought the formation process of the first stars is
relatively well understood, and leads to the formation of
predominantly very massive stars.
At some later stage, star formation in the universe appears to be
dominated by a near universal Initial Mass Function, biased
towards low mass stars, with an approximate power law dependence
between the number of stars formed and their mass, over
a factor of a few hundred in mass.
We explore the effect of metallicity on fragmentation in cold low
metallicity gas, using a new implementation of radiative cooling
combined with adaptive mesh refinement simulations of the gas
dynamics under gravity. Given some simplifying assumptions, we
find a transition to the normal mode of star formation, evidence for
an intermediate third mode of star formation, and discuss
some of the physical issues and possible implications, including
prospects for non-standard star formation modes in the present universe.