How cosmic rays get started

Supernovae (SN) of Type II and Ia, with their expanding shock fronts, are considered to be the main agents of cosmic-ray acceleration. In early models of SN shock theory, the thermal gas in the interstellar medium (ISM) was regarded as the reservoir of seed particles which can become cosmic-ray nuclei. This assumption, however, conflicts with the source composition of the Galactic cosmic rays (GCR). The model of origin described here seeks to resolve this contradiction by invoking an injection of suprathermal ions, mainly from the coronae of dMe and dKe dwarfs - by far the most numerous stars in the Galaxy. The ions are energized (to MeV energies) via coronal mass ejections (CME). Then, encountering a supernova shock, they are accelerated to CR energies. While earlier versions of this scenario ascribed the origin to flares, it is now thought that the production of energetic particles in solar and red-dwarf atmospheres is mainly due to CME. Accordingly the energy budget for injection has been revised to take account of the newer paradigm. The probability that the seed particles will meet an "active" SN shock is estimated, and found to be adequate. In sum, dMe and dKe stars seem to be a promising class of CR injectors. Also discussed briefly are alternative models of injection.