with each other. As these stars grow, 
they eventually reach the stage at 
which they become unstable and ex- 
plode in supernovae outbursts that 
supply energy to the galactic nucleus. 
The problem with this theory of co- 
alescence by means of collisions is 
similar to the problem with the theory 
of disruption due to collisions. As a 
consequence of developing a concen- 
tration of stars sufficient for the nec- 
essary collisions to occur, the cluster 
or part of the cluster would have to 
shrink into a single supermassive star 
or a black hole in a period of time 
shorter than the period necessary to 
account for the frequency with which 
the active galactic nucleus is observed. 
The conclusion is that dense star 
clusters may be the precursors of qua- 
sars and Seyfert nuclei, but that the 
phenomenon of actual active galactic 
nuclei must be related to one of the 
other two forms of enormous concen- 
trated mass that have been proposed, 
namely, supermassive stars or black 
holes. 
The mass concentration that was 
first considered as a possible source 
of quasar energy was in fact the 
supermassive star. The relation be- 
tween the rate of energy emission and 
the mass of a supermassive star is 
well known and the power necessary 
for an average active galactic nucleus 
could be provided by a supermassive 
star with a mass of about ten million 
suns. (If an object of that mass were 
in the sun’s position relative to the 
earth, its radiant energy would create 
a temperature of about 50,000° F on 
the earth.) The most luminous quasars 
could be powered by a supermassive 
star with a mass of about 500 million 
suns. However, a supermassive star 
of these proportions would not be sta- 
ble. Calculations show that a super- 
massive star having a mass of more 
than about 700,000 suns would col- 
lapse irreversibly unless it were ro- 
tating so rapidly that it would become 
flattened and so fractured that it 
would probably no longer have the 
characteristics of a star. 
Thus, the concentration of mass into 
a supermassive star capable of power- 
ing an active galactic nucleus would 
apparently almost immediately result 
in collapse into a black hole. Since 
a dense star cluster of sufficient mass 
to power an active galactic nucleus 
would ultimately produce a super- 
massive star or a black hole, and since 
a supermassive star of such propor- 
tions would in a very short time col- 
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