Deciphering particle acceleration in massive-star environments with gamma-ray modelling and MHD simulations

Several young star clusters show degree-scale diffuse gamma-ray emission, hinting at ongoing particle acceleration. Despite these detections, acceleration sites remain largely unidentified and transport properties are not well constrained. Addressing both questions can provide essential information on the origin of multi-PeV comsic rays and on Galactic particle transport. A key difficulty is that the environments of young star clusters are shaped by large-scale (~100 pc) feedback from massive stars. Wind-wind interactions create intricate flow and magnetic field structures, which affect cosmic ray acceleration and transport in non-trivial ways. Here, 3D (M)HD simulations can provide insights, which in turn serve as bases for acceleration and transport models. I present simulations of wind-wind interaction in young star clusters and discuss their implications. In addition, I discuss the recent detection of PeV gamma-rays from the Cygnus region and demonstrate that a 50 kyr-old energetic supernova remnant can accelerate particles to the required energies.