Galactic cosmic ray: Encyclopedia II – Galactic cosmic ray – Where do they come from?
Most galactic cosmic rays are probably accelerated in the blast waves of supernova remnants. This doesn’t mean that the supernova explosion itself gets the particles up to these speeds. The remnants of the explosions, expanding clouds of gas and magnetic field, can last for thousands of years, and this is where cosmic rays are accelerated. Bouncing randomly back and forth in the magnetic field of the remnant lets some of the particles gain energy and become cosmic rays. Eventually they build up enough speed that the remnant can no longer contain them, and they escape into the Galaxy. Acceleration by the shock front expanding from the supernova is apparently an important process. This seems confirmed by the HESS Cerenkov telescope array in Namibia, which observed high energy gamma rays originating in a ring around an old supernova. Shock accceleration (to much lower energies) has also been observed in the Earth’s magnetosphere. Because the cosmic rays eventually escape the supernova rem
