Magnetohydrodynamics of population III star formation

Jet-driving and fragmentation processes in a collapsing primordial cloud are studied using three-dimensional MHD nested grid simulations. Starting from a rotating magnetized spherical cloud with a number density of n_c ≃ 10³ cm^-3, we follow the evolution of the cloud until the adiabatic core (or protostar) formation epoch, n_c ≃ 10²² cm^-3. We calculate 36 models parameterizing the initial magnetic γ₀ and rotational β₀ energies. The evolution of collapsing primordial clouds is characterized by the ratio of the initial rotational energy to the magnetic energy, γ₀/ β₀. The Lorentz force significantly affects cloud evolution when ̂₀ > β₀, while the centrifugal force dominates the Lorentz force when β₀ > γ₀ When the cloud rotates rapidly with an angular velocity of Ω₀ > 10^_171(n_c/10³ cm^_3) ^2/3 s^-11 and β₀ > γ₀, fragmentation occurs before protostar formation, but no jet appears after protostar formation. On the other hand, when the initial cloud has a magnetic field of B₀ > 10^_911(n_c/10³ cm^_3)^2/3 G and γ₀ > a strong jet appears after protostar formation without fragmentation. Our results indicate that Population III protostars frequently show fragmentation and protostellar jets. Population III stars are therefore born as binary or multiple stellar systems; as in present-day star formation, they can drive strong jets that disturb the interstellar medium significantly, and thus they may induce the formation of next-generation stars.