What astronomical sites are the most likely production sources for Galactic Cosmic Rays (GCRs)?

Answer

Supernova remnants

Galactic Cosmic Rays (GCRs) originate outside the solar system, tracing their sources back to violent astronomical events, most likely the intense shock waves generated by supernova remnants.

What astronomical sites are the most likely production sources for Galactic Cosmic Rays (GCRs)?
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