Cosmic rays in superbubbles: spectra and composition above the knee

Models of nonthermal particle acceleration in the vicinity of active star forming regions are reviewed. We discuss a collective effect of both stellar winds of massive stars and core collapsed supernovae as particle acceleration agents. Collective supernova explosions with great energy release in the form of multiple interacting shock waves inside the superbubbles are argued as a favourable site of nonthermal particle acceleration. The acceleration mechanism provides an efficient creation of a nonthermal nuclei population with a hard low-energy spectrum, containing a substantial part of the kinetic energy released by the winds of young massive stars and supernovae. We discuss a model of temporal evolution of particle distribution function accounting for the nonlinear effect of the reaction of the accelerated particles on the shock turbulence inside the superbubble. Hard spectrum extends up to a break energy that depends strongly on the nuclei injection rate. The model illustrates that both the low-energy metal-rich nonthermal component and the standard galactic cosmic rays could be efficiently produced by superbubbles at different evolution stages.