A W Wolfendale
Articles written in Pramana – Journal of Physics
Volume 12 Issue 6 June 1979 pp 631-651 Astrophysics
Cosmic rays were discovered in 1911 but it is only now that some ideas are beginning to emerge as to their origin. This paper will examine the present evidence concerning the origin question over the whole energy range, from 109 eV to 1020 eV.
At the lowest energies, (109–1010 eV), the new subject of gamma ray astronomy plays a crucial role and a galactic origin is favoured. At higher energies (1012–1017 eV) recent measurements of the anisotropies in arrival directions also suggest a galactic origin, although the evidence is not as strong.
At the very highest energies it seems likely that some, at least, of the particles come from outside the galaxy although the non-existence of the cut-off at about 6 × 1019 eV arising from interactions with the cosmological relict radiation provides a paradox. The likely future areas of advance in this fascinating subject will be indicated.
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