The Origin of Cosmic Rays

Abstract

A brief discussion of present ideas concerning the origin of cosmic rays is given. Arguments are then given to show that the strong extragalactic radio sources are short­ lived with time-scales :::;106 years. If we now accept the concept of the local supercluster of galaxies, it is shown that the frequency of strong radio sources is sufficient to produce an energy density of cosmic rays in this supercluster of the order of 10-13-10-12 erg/cms. Thus it is possible that the extragalactic component of cosmic rays arising in the super­ cluster (i. e_ within distances of -30 Mpc of our Galaxy) is appreciable, and it might account for the majority of the. cosmic rays in the Galaxy. Some consequences of this hypothesis are examined. § I. Introduction In the last decade ideas concerning the origin of cosmic rays have been much advanced through the observation of nonthermal radio sources both inside and outside our Galaxy. It is our purpose in this paper to propose a variation on current ideas which have been summarized by Ginzburg1l and Ginzburg and Syrovatsky.2J,SJ Let us first summarize very briefly the main arguments of those authors. They conclude that the .most probable place of origin of the cosmic rays is in supernovae and novae. They have argued that although objects like the sun or prculiar stars may produce cosmic rays, reasonable estimates of their efficiency of production suggest that such sources make only a negligible con­ tribution to the energy density. The observed relative abundances of the ele­ ments· in the primary cosmic radiation are such that there is an excess .of all elements heavier than helium relative to the abundances derived from analyses of the solar system material and nearby stars. This is explicable either by sup­ posing (1) that the cosmic rays arise in regions where there is a deficiency of hydrogen and helium, or (2) that in the sources there is a preferential acceler­ ation of heavier ions. In both cases we must take into account the modification of the cosmic ray composition due to nuclear collisions anywhere in the path between the place of acceleration and the top of the earth's atmosphere. This path length is determined by the relative numbers of lithium, beryllium, and boron nuclei relative to the other elements. These nuclei cannot have been present in the so~rces because they are rapidly destroyed in high-temperature regions, i.e. at some stage of stellar evolution these nuclei, if they are present,