How massive were the first stars ?
This question is of fundamental importance for galaxy formation and cosmic reionization .
Here we consider how protostellar feedback can limit the mass of a forming star .
For this we must understand the rate at which primordial protostars accrete , how they and their feedback output evolve , and how this feedback interacts with the infalling matter .
We describe the accretion rate with an “ isentropic accretion ” model : \dot { m } _ { * } is initially very large ( 0.03 { M _ { \odot } yr ^ { -1 } } when m _ { * } = 1 { M _ { \odot } } ) and declines as m _ { * } ^ { -3 / 7 } .
Protostellar evolution is treated with a model that tracks the total energy of the star .
A key difference compared to previous studies is allowance for rotation of the infalling envelope .
This leads to photospheric conditions at the star and dramatic differences in the feedback .
Two feedback mechanisms are considered : HII region breakout and radiation pressure from Lyman- \alpha and FUV photons .
Radiation pressure appears to be the dominant mechanism for suppressing infall , becoming dynamically important around 20 { M _ { \odot } } .