The question of selective absorption of light in space viewed from the viewpoint of the dynamics of the universe

Abstract

The selective light absorption in space has been raised in astronomical literature. The substance producing the absorption must have some mass; thus the question is how large it is. We develop a dynamical model of the Milky Way system, assuming that it can be represented by a flattened ellipsoid of rotation. We use the spatial distribution of $\delta$-Cephei and Algol type variable stars, and mean velocities of stars according to Campbell to calculate the dynamical density of the Milky Way near the Sun, $0.100\,M_\odot/pc^3$. We find that the dynamical density is equal to the mean density of stars in the vicinity of the Sun. Our conclusion is that the intrinsic gravity of stars fully explains their motion, and the existence of any other matter in any significant quantity seems unlikely. Therefore, the existence of noticeable selective absorption seems to be absolutely improbable, unless one admits the existence in the space of particles much smaller than atoms of elements known to us. Normal absorption may exist if the particle diameter is of the order of a millimetre or less, and their mass is comparatively small. This absorption has not yet been reliably detected; the fact that the number of stars increases with stellar magnitude more slowly than theory requires in case of uniform distribution of stars in space, can be equally explained by both light absorption and decrease in number of stars with distance.