154 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1949 
four hydrogen atoms weigh 0.7 percent more than one helium atom, 
the additional mass is released as energy and can be radiated by the 
star. Even if a star is originally all hydrogen, the total mass radiated 
can evidently not exceed a very small fraction of the mass of the star. 
As a result of these findings we now know that the universe has 
apparently not lasted long enough in its present form for stars to 
radiate much of their mass, and in any case there seems to be no 
physical process by which a star could radiate away most of its mat- 
ter even if there were time enough. We are forced to conclude that 
the present variety of stars in the sky is the result of the original 
method of star formation rather than of any evolutionary process. 
And the formation of stars in general is still a closed book, since the 
explosion of the universe a few billion years ago has so far defied 
any attempts at detailed analysis. It is even possible that the basic 
laws of nature may have been quite different at that time. Thus 
our research in the direction of general stellar evolution reminds one 
of Browning’s philosopher, who had 
. written three books on the soul, 
Proving absurd all written hitherto 
And putting us to ignorance again. 
SUPERGIANT STARS 
While the origin of the universe is still beyond our understanding, 
some progress has been made in explaining the origin of a certain class 
of stars, which may have been created relatively recently. A super- 
giant star is one which radiates light and heat some ten thousand 
times as strongly as ourown sun. There are not many of these stars, 
but in a galaxy of many billions of lesser stars they stand out in the 
same way that a searchlight stands out from a swarm of fireflies. 
These stars are burning their candle at both ends and they cannot 
last very long, astronomically speaking. Within a mere hundred 
million years, such a star must burn all its hydrogen into helium. 
There is no known way in which a star can remain dark for a long 
period of time and then suddenly start shining. We conclude that 
these supergiant stars have formed within the last hundred million 
years—less than a tenth of the age of the universe. 
Of course, it is possible that nuclear physicists have overlooked 
some important process by which a star can radiate a much larger 
fraction of its mass than the hydrogen-into-helium process liberates. 
This does not seem very likely, since the energies with which the atoms 
hit each otherinsidea star average only a few thousand electron volts— 
a small fraction of the energies developed in such atom-busting devices 
as the cyclotron and synchrotron—and since the nuclear reactions 
produced at low energies have been fairly well explored in the lab- 
oratory. 
