Where and how do cosmic rays originate? As yet, no one really knows, but reasonable hypotheses have been put forward, and this article focuses attention on supernovae as an important set of likely sources.Since the discovery, about half a century ago, of the cosmic radiation, its manifestations on earth have been extensively explored and considerably elucidated. Within the atmosphere, the radiation comprises an almost bewildering melange of atomic nuclei, electrons, positrons, energetic photons, and all of the other known "elementary" particles. Most of the latter were, in fact, first discovered in the cosmic radiation-for example, the penetrating muons (1, 2), the principal component at sea level. These radioactive particles arise mainly as the progeny of unstable pi mesons; the pions, in turn, are generated in violent nuclear collisions at higher altitudes.Also spawned in these strong interactions are "strange particles"-the Kmesons and hyperons (2). Just a decade ago, the only source of these intriguing, short-lived particles was the cosmic radiation. In the ensuing years man-made "cosmic rays" have become available-at least up to energies of some tens of billions of electron volts (see appendix)-and tors are spewing forth and well-directed beam and even anti-protons. task of probing the na actions of mesons, nucl antiparticles is mainly 1 laboratory high-energy though at the higher f yet unattainable with m rays are still a necessai Our concern in the pr is not with the rich ass ondary particles terresti whether by nature or b are, rather, concerned w cosmic rays per se, frc incident upon the eart rections. They consist, know, of protons, helii still heavier nuclei, po energies E comparable ing their rest masses. 1 cordingly, with speeds light, c.It has long been k total energy arriving a cosmic rays is quite reaching us as starligh eluded). This correspon density in space of The comparison with means implies that the r strengths required for tl radiation are comparat to the copious loss of galaxy that results from the rectilinear propagation and easy escape of photons, the cosmic-ray ions are, as we shall see, trapped and stored by the magnetic fields of interstellar space. aS Thus, a much lower rate of energy production than that required for stares light suffices to yield the observed energy density. Nevertheless, if a cosmic-ray energy density of similar magzed nitude characterizes all or much of the galactic space, then it follows that a m .formidable store of energy is concentrated in a relatively modest amount of matter. How this remarkable concentration of energy into relativistic particles comes about is one of the central problems confronting any theory of cosmic-ray origin. giant accelera-It will be useful, before describing fairly intense the supernova theory, to review ceris of K-mesons tain salient features of the cosmic So, today, the radiation and of the galaxy, and also ture and interto recall some of Fermi's ideas on the leons, and their statistical acceleration of ions by "colthe province o...
