419 
388-390] The Annihilation of Matter 
have been spent as a “white dwarf.” The matter in these stars is protected 
from annihilation, with the result that they are so feebly luminous for their 
mass as to upset all calculations. We have no means of knowing whether 
the sun, or any other star, has spent part of its life as a white dwarf or not. 
Theory is not altogether hostile to such a possibility, while observation is 
necessarily silent on the matter since white dwarfs are so faint that the vast 
majority of them escape observation entirely. 
Similarly, the dense central nuclei of the spiral and other extra-galactic 
nebulae probably consist of matter which is broken up into its ultimate 
constituent parts and so is immune from annihilation. These nebulae are in 
effect vast storehouses of matter which is immune from annihilation and on 
which age produces no effect. Thus those stars which look the youngest may, 
although this is hardly likely, actually consist of the oldest atoms, and, in any 
case, it becomes impossible to divide either stars or atoms up into young and 
old. It is possible, although again perhaps hardly likely, that all atoms may 
-originally have come into being at the same time. 
390 . We have seen that the observed radii of stars of large mass fall into 
distinct detached groups, the different radii being easily identified as corre 
sponding to the various rings of electrons which revolve round the atomic 
nucleus. The group of stars whose radii are smallest of all, the white dwarfs, 
consist mainly of atoms stripped bare of electrons right down to their nuclei. 
The next group, the main sequence stars, have atoms in which only one ring 
of electrons, the K- ring, is left. The next group, the giant stars, have two 
rings left, and so on. For the temperatures in the inner regions of the stars to 
break up the atoms to the extent required for this identification, we have found 
that the stellar atoms must have atomic numbers in the neighbourhood of 95. 
If the stars were made of terrestrial atoms, the high interior temperatures 
of the stars would strip most of the atoms bare down to their nuclei. The com 
pletely broken up atoms would now behave almost like a perfect gas, and this 
would make the star unstable, since we have found that a perfectly gaseous 
star generating its energy spontaneously cannot be in stable equilibrium. To 
keep the stars stable two separate conditions are necessary. The first, already 
mentioned, is that the stellar atoms must liberate their energy spontaneously, 
as the radioactive elements do; the second requires that they must have 
atomic numbers somewhere in the neighbourhood of 95 which is just higher 
than the atomic numbers (84—92) of the radioactive elements. 
The atomic number of any atom is the number of electrons which revolve 
round the nucleus when the atom is complete, and this gives a measure of the 
complexity of structure of the atom. Our conclusion, then, is that stellar 
atoms are rather more complex than the most complex of terrestrial atoms, 
namely, the radioactive atoms. We may regard the stellar atoms, in a sense, 
as super-radioactive atoms. The sequence from these through the ordinary