Inside the core of a young massive star cluster: 3D MHD simulations

Abstract

ABSTRACT Young massive star clusters inhabit regions of star formation and play an essential role in the galactic evolution. They are sources of both thermal and non-thermal radiation, and are effective cosmic ray accelerators. We present the 3D magnetohydrodynamic modelling of the plasma flows in a young compact cluster at the evolutionary stage comprising multiple interacting supersonic winds of massive OB and WR stars. The modelling allows studying the partitioning of the mechanical energy injected by the winds between the bulk motions, thermal heating, and magnetic fields. Cluster-scale magnetic fields reaching the magnitudes of ∼300 $\mu$G show the filamentary structures spreading throughout the cluster core. The filaments with the high magnetic fields are produced by the Axford–Cranfill-type effect in the downstream of the wind termination shocks, which is amplified by a compression of the fields with the hot plasma thermal pressure in the central part of the cluster core. The hot (∼a few keV) plasma is heated at the termination shocks of the stellar winds and compressed in the colliding post-shock flows. We also discuss a possible role of the thermal conduction effects on the plasma flow, and analyse temperature maps in the cluster core and the diffuse thermal X-ray emission spectra. The presence of high cluster-scale magnetic fields supports the possibility of high-energy cosmic ray acceleration in clusters at the given evolutionary stage.