The Origin of Cosmic Rays: How Their Composition Defines Their Sources and Sites, and the Processes of Their Mixing, Injection and Acceleration

TL;DR

This paper explains the composition of galactic cosmic rays as a result of mixing, injection, and acceleration processes in supernova remnants, revealing how their source abundances are shaped by these astrophysical phenomena.

Contribution

It introduces a comprehensive model linking supernova ejecta mixing, grain sputtering, and shock acceleration to cosmic ray composition, matching observed abundances without free parameters.

Findings

Cosmic ray compositions reflect mixing of supernova ejecta and interstellar medium.

Grain sputtering and injection processes significantly influence cosmic ray abundances.

Model predictions align with observed cosmic ray elemental ratios within 35%.

Abstract

Galactic cosmic-ray source compositions, (Z/H)GCRS from H to Pb and ~10^8 - 10^14 eV, differ from solar-local interstellar, (Z/H)SS or (Z/H)ISM by ~20-200x. Both are mostly just mixes of core collapse (CCSN) and thermonuclear (SN Ia) supernova ejecta. The (Z/H)ISM come from steady unbiased accumulation over Gyrs. But the cosmic ray mass mixing ratio, universal ISM/CCSN ~4:1 of swept-up ISM and ~10x metallicity ejecta show that (Z/H)GCRS come from basic Sedov-Taylor bulk mixing of homologous, expanding CCSN in their OB cluster self-generated superbubbles, further enriched by highly biased grain-sputtering injection during diffusive shock acceleration (DSA). Moreover, this mixing ratio now reveals that the cosmic rays are primarily accelerated as their evolving reverse shock radius and energy passes through their maxima. Refractories and volatiles, first deposited in fast ejecta and ISM grains in freely expanding ejecta, are simultaneously Coulomb-sputtered FCS by turbulent H and He as suprathermal ions into DSA that carries them to cosmic-ray energies. This bulk mixing selectively increases source mix abundancies (Z/H)SM / (Z/H)SS by ~2-10; and injection by grain condensation and implantation fractions FGC, by another ~6, while Z^0.67 Coulomb grain sputtering enrichments FCS give an added ~4-20. Applying these basic processes of mixing and injection to solar system (Z/H)SS produces grain-injected, source-mix (Z/H)SMGI that match major cosmic ray abundances (Z/H)GCRS to within 35 % with no free parameters. Independently confirming grain injection, (Z/H)GCRS shows no detectable contribution of Fe from SN Ia, although producing ~1/2 Fe in ISM, but there is also no dust in SN Ia remnants, unlike CCSN.