a large concentration of mass that sup- 
plies the energy for active galactic 
nuclei. Supermassive stars with 
masses of between about 500,000 suns 
and masses of about 700,000 suns have 
just that property. They are unstable, 
but instead of collapsing into black 
holes, as do supermassive stars having 
masses greater than 700,000 suns, 
they suffer violent nuclear explosions. 
In each explosion, enough energy 
would be released to power a luminous 
Seyfert galaxy for about 30,000 years. 
Not all the energy of the explosion 
would be expected to be converted 
to radiant energy, but even if only 
10 percent were, there would be 
enough energy to power a Seyfert gal- 
axy for 3,000 years. Since the activity 
in the nucleus must go on for a total 
of 100 million years, then 30,000 rep- 
etitions of a supermassive star out- 
burst would have to occur. The ma- 
terial at the center of spiral galaxies 
would have to grow into a super- 
massive star with a mass of about 
500,000 suns in order to cause a vio- 
lent explosion. Therefore the total 
amount of material that would have 
to be processed in order to power a 
luminous Seyfert galaxy would be 
equal to the mass of ten billion suns. 
A mass of ten billion suns is about 
5 percent of the mass of a normal 
spiral galaxy such as our Milky Way. 
In order to power a luminous quasar, 
all the mass of a normal galaxy would 
have to be processed, a quite unlikely 
situation. 
There are many ifs and maybes, 
however. Maybe the parent galaxies 
of quasars are much larger than nor- 
mal spiral galaxies. Maybe the quasars 
are not as long-lived as the Seyfert 
galaxies and don’t have to process as 
much material as it seems. Whatever 
the case, the mechanism by which the 
energy of the active nuclei of galaxies 
is generated is not at this time well 
understood and our theories regarding 
the accretion of black holes and the 
explosions of supermassive stars must 
be classified as speculation. 
Astronomers studying quasars and 
Seyfert galaxies continue to provide 
observational data. As these data are 
analyzed, we hope to come closer to 
a true understanding of how the nuclei 
of these objects really work. 
Eugene R. Capriotti is chairman of 
the Department of Astronomy at Ohio 
State University and director of the 
Perkins Observatory of Ohio State 
and Ohio Wesleyan Universities. 
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