Absorption of Cosmic Rays in the Milky Way

Abstract

If cosmic rays are of extragalactic origin, they must be partially absorbed by the gas and dust clouds which populate the interstellar spaces. This absorption will produce directional asymmetries in the intensity of the cosmic rays because of our eccentric location relative to the Milky Way. In addition to the straight absorption of energy a part of the cosmic rays will be scattered by interstellar matter without appreciable loss in total energy. Such scattering includes the formation of energetic secondaries and therefore tends to produce a change in the numbers and physical characteristics of the various constituents of the cosmic rays. Again, because of the segregating action of the earth's magnetic field, directional asymmetries will result. Although the effects to be expected are in all probability small it seems that modern instruments are sufficiently sensitive to make possible the detection of the before-mentioned asymmetries. Positive results of a search for absorption effects might furnish new information on (1) Whether or not cosmic rays are of extragalactic origin. (2) The problem of the total amount of interstellar matter. (3) The analysis of the composition of cosmic rays.