| Abstract : | Cosmic rays (CRs) are high-energy particles that span an extensive energy range from 1 GeV to ∼ 10^11 GeV. CRs up to ∼ 10^(5-6)GeV are believed to be accelerated by supernova shocks, and the extra-Galactic CR contribution dominates in the range above 10^9 GeV. So some other unknown sources must exist that dominate the CR spectrum in between. Our work shows that stellar winds from massive young star clusters can explain Galactic cosmic rays (CRs) in the 10^7 GeV to 10^9 GeV range. The wind termination shock (WTS) in these star clusters is strong enough to accelerate particles in this energy range, which is difficult to reach in the standard paradigm of CR acceleration in supernova remnants. We present a model for producing different nuclei in CRs from massive stellar winds using the observed distribution of young star clusters in the Galactic plane and the abundances of stellar wind. We present a detailed calculation of CR transport in the Galaxy, considering the effect of diffusion, interaction losses, and re-acceleration by older supernova remnants to determine the all-particle CR spectrum. Using the observed magnetic field values in molecular clouds (where the star clusters are generally embedded), we argue that the WTS can accelerate protons up to a few hundred PeV (10^8 GeV). To match the observed data with our model, we need an exponential energy cutoff of (3 − 4) × 10^8 ? GeV and a cosmic-ray injection fraction of ∼ (5 − 7)% from the clusters. These parameter values vary slightly with different models of the extra-galactic (≳ 10^9 GeV) cosmic rays. Therefore, we argue that this CR component originating from star clusters can be considered the natural ‘second component’ of Galactic cosmic rays along with the existing CR component accelerated in the shocks of regular supernova remnants.
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