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/r type distribution of CRs, which indicates a continuous injection of CRs in these objects. The hard, ∝ E - 2.3 type 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. [ABSTRACT FROM AUTHOR]