Magneto-Hydrodynamics of Population III Star Formation
Abstract
Jet driving and fragmentation process in collapsing primordial cloud are studied using three-dimensional MHD nested grid simulations. Starting from a rotating magnetized spherical cloud with the number density of n=103 cm-3, we follow the evolution of the cloud up to the stellar density n=1022 cm-3. We calculate 36 models parameterizing the initial magnetic and rotational energies (γ0, β0). In the collapsing primordial clouds, the cloud evolutions are characterized by the ratio of the initial rotational to magnetic energy, γ0/β0. The Lorentz force significantly affects the cloud evolution when γ0 > β0, while the centrifugal force is more dominant than the Lorentz force when β0 > γ0. When the cloud rotates rapidly with angular velocity of 0 > 10-17 (n/103 cm-3)2/3 s-1 and β0 > γ0, fragmentation occurs before the protostar is formed, but no jet appears after the protostar formation. On the other hand, a strong jet appears after the protostar formation without fragmentation when the initial cloud has the magnetic field of B0 > 10-9 (n/103 cm-3)2/3 G and γ0 > β0. Our results indicate that proto-Population III stars frequently show fragmentation and protostellar jet. Population III stars are therefore born as binary or multiple stellar systems, and they can drive strong jets, which disturb the interstellar medium significantly, as well as in the present-day star formation, and thus they may induce the formation of next generation stars.