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

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 they are effective cosmic ray accelerators. We present the 3D magnetohydrodynamic (MHD) modeling 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 modeling 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 μG 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 postshock flows. We also discuss a possible role of the thermal conduction effects on the plasma flow, 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.

Particle acceleration in superbubbles: MHD simulations and $\gamma$-ray signatures

“…In interacting the winds in the core, magnetic field strength of up to ∼500 G were found. Fields of similar scale were found in earlier work [8]. According to [7], such fields are sufficient to allow particle acceleration to PeV energies at supernova shocks expanding in the low-density bubble interior at a high speed.…”

“…In this section, we report on magneto-hydrodynamic (MHD) simulations of the core of a young massive stellar cluster and its wind bubble. With our setup, we extend previous work covering the core [8] to larger scales. Complementary work using HD simulations is also published in these proceedings [9].…”

Mixing of materials in magnetized core-collapse supernova remnants

“…Indeed, the regions filled by the winds turned to be isolate islands located around the shell made of the circumstellar medium shocked by the blastwave, where the material is both subsonic and superalfvenic. Such work should be extended to the stellar clusters made of multiple massive stars (Badmaev et al 2022).…”

Star clusters as cosmic ray accelerators

“…These estimates of are disappointing, as the acceleration of protons well beyond PeV energies is required to explain the smooth observed transition between Galactic and extragalactic CRs. A way to overcome this problem is to speculate that ≫ PeV particles are accelerated at very fast SNR shocks expanding within the collective wind launched by a compact cluster [40] (the magnetic field is expected to be large in such an environment [41]). The required shock speed would be of the order of ≈ 30000 km/s [40], but this would in turn correspond to an explosion energy of ≈ 10 52 ( / ⊙ ) ( /30000 km/s) 2 erg, i.e.…”