Prof. Biman Nath

The detection of gamma-rays from massive young star clusters in recent years has re-ignited an old idea that star clusters can accelerate a significant component of Galactic cosmic rays (GCR).I will present our recent work on simulating massive star clusters and how multi-wavelength studies can help us identify the shocks that can accelerate cosmic rays in star clusters. Our work shows the termination shock of stellar winds as an important acceleration site. One interesting test of this idea is the isotopic ratio of Neon(22)/Neon(20) in GCR because it is much larger than that expected from the standard paradigm of cosmic rays acceleration in supernova remnants. Recently, we have been able to explain this isotopic ratio by bringing star clusters into the picture. I will argue that star clusters can account for at least a quarter of the Galactic cosmic rays. I will also discuss how this picture relates to the old idea of nested leaky-box model, and how star clusters can solve the Pevatron problem for GCR, as well as some implication for the diffuse gamma-ray background in our Galaxy.