Cosmic rays—astronomy with energetic particles

Since the discovery of the cosmic radiation the question of the origin of these high‐energy particles has been an astrophysical problem of foremost importance. Rapid progress toward an understanding of this problem has been made in the past ten to twenty years as experimental techniques became available that permitted a study of the cosmic radiation either near the outer fringes of the atmosphere, with high‐altitude balloons, or in space, totally uninhibited by the Earth's atmosphere. The picture that has unfolded displays an enormous variety. All nuclei in the periodic table of the elements, as well as electrons and positrons, are present in the stream of cosmic‐ray particles; their energies span the range from at least ${10}^6\hspace{0.17em}\mathrm{eV}$ to ${10}^{20}\hspace{0.17em}\mathrm{eV}.$ What objects inside or outside our galaxy produce these extremely high‐energy electrons and nuclei of the entire periodic table?