EVOLUTION OF STARS—ABBOT 181 
fully absorbed that they are quite unable to penetrate from within 
to the star surface. Hence the supply of energy fails to quite main- 
tain the outside temperature required to keep up the immense radia- 
tion of such a star to space. Our sun, for instance, gives out each 
year as much energy of radiation as four hundred thousand billion 
of billions of tons of anthracite coal, and it is believed that the in- 
creasing temperature of the sun’s interior more and more hinders 
the communication of energy to supply its surface loss. 
So the surfaces of the dense stars cool while they are still raging 
hot within, and from these cooling surfaces we receive the dimin- 
ished light which gives the declining spectrum series associated with 
dwarf stars. 
12. But how about the energy to support such enormous radiation ? 
Surely it can not come indefinitely from shrinkage. The study of 
radium and uranium bearing rocks has proved that our earth in its 
present stage has had a duration of quite a billion years, and the 
fossil story shows that life was well organized quite as long ago. 
Shrinkage of the sun can not account for a supply of heat to warm 
the earth for the support of life so long as that. 
As we have seen, the annihilation of an atom by the falling in 
of its two kinds of electricities must give up the energy of motion 
which the electrons possessed as an atom. It is now conceived that 
at the exalted temperature and tremendous pressure within the 
denser stars, conditions are right for the annihilation of their atoms, 
with liberation of their energy to support radiation. 
13. To recapitulate the probable course of evolution of stars: Out 
of the formless nebula, whose atoms were brought into being by 
some means of creation which we do not possess or understand, red 
giant stars, far less dense than air, were formed. Under the com- 
bined influences of gravitation and radiation, these giant stars grew 
hotter and denser. With rising surface temperatures, their colors 
advanced through yellow to white and blue, attended by the familiar 
changes of spectra, and by a great decrease in diameter, but with- 
out much change of total brightness. Arrived at temperatures so 
superlative and densities so considerable, the flow of radiation from 
within to heat the surface is hindered by absorption owing to short- 
ness of average wave length, so that the surfaces no longer maintain 
their maximum temperature or radiation. Yet the inner tempera- 
tures continue rising because the stars, though so dense, retain the 
characters of perfect gases. For their atoms are reduced by separa- 
tion of nuclei and electrons. The process of cooling at the surface 
continues until the star, born a red giant, dies a red dwarf, having 
not only attained great density by contraction but lost much mass 
by annihilation. 
20837—27-——13 
