MHD simulations of dense core collision

Abstract

We investigated the effect of magnetic fields on the collision process between dense molecular cores. We performed three-dimensional magnetohydrodynamic simulations of collisions between two self-gravitating cores using the Enzo adaptive mesh refinement code. The core was modeled as a stable isothermal Bonnor-Ebert (BE) sphere immersed in uniform magnetic fields. Collisions were characterized by the offset parameter $b$, Mach number of the initial core $\mathcal{M}$, magnetic field strength $B_{0}$, and angle $\theta$ between the initial magnetic field and collision axis. For head-on ($b = 0$) collisions, one protostar was formed in the compressed layer. The higher the magnetic field strength, the lower the accretion rate. For models with $b = 0$ and $\theta = 90^{\circ}$, the accretion rate was more dependent on the initial magnetic field strength compared with $b = 0$ and $\theta = 0^{\circ}$ models. For off-center ($b = 1$) collisions, the higher specific angular momentum increased; therefore, the gas motion was complicated. In models with $b = 1$ and $\mathcal{M} = 1$, the number of protostars and gas motion highly depended on $B_{0}$ and $\theta$. For models with $b = 1$ and $\mathcal{M} = 3$, no significant shock-compressed layer was formed and star formation was not triggered.