Massive star clusters as the an alternative source population of galactic cosmic rays

Extended γ-ray emissions in the vicinity of young star clusters are believed to be produced by the interaction of CRs accelerated therein with the ambient gas. The detailed spatial analysis reveals 1/rtype distribution of CRs, which indicates a continuous injection of CRs in these objects. The hard, ∝E-2.3type power-law energy spectra of parent protons continue up to ∼1 PeV. The efficiency of conversion of kinetic energy of powerful stellar winds to CRs can be as high as 10%. This implies that the young massive stars can operate as effective proton PeVatrons with a major or even dominant contribution to the flux of highest-energy galactic CRs.