The Physics of Cosmic Grains.

The present paper is primarily concerned with a critical analysis of existing theories on the formation of "cores" of condensation and crystals in interstellar space and with the growth (or lack of growth) of the cosmic grains and their electrical charges. It appears very unlikely that the formation of cores of condensation and of the existing grains out of the interstellar gas is continuing under existing average conditions. As an alternative hypothesis to explain the origin of the cosmic grains, we suggest that they were formed in the early stages of the ex- pansion of the universe when the critical conditions of saturation were realized. We have applied, with certain modifications, the s~ave-mechanica1 theory for the interaction of gas particles with the surfaces of crystals developed by Lennard-Jones and his co-workers. The derived value for the accommodation coefficient for the cosmic gas on the cosmic grains is a<O.35. From this value it is found that the surface of a grain at 3° K produces a perturbation on the average velocity of a collid- ing atom with a speed corresponding to 10,0000 K but that this perturbation is not strong enough to produce appreciable absorption. The escaping atoms will have, on the average, a velocity temperature greater than 6500° K. We conclude, therefore, that the cosmic grains cannot grow by an adsorption process. An analysis of the probable electrical charges of the cosmic grains points to certain weak points in the theories of Jung and Spitzer. We arrive at the conclusion that the metallic cosmic grains would, in the H ii region, have a positive electrical potential when the dilution coefficient, W, is greater than 10-12, whereas for W = 1O'~ the potential is -0.7 volts. In the H i regions, which occupy 90 per cent of inter- stellar space, the electrical potential is probably +0.8 volts. Since at least a fraction of the cosmic grains are, in all probability, dielectric substances, we consider the probable electrical potentials also for this case. We conclude that they are positive, but small