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FREE CATALOG 
Wallace is without 
question one of the best 
nature writers of our 
day.” — Country Journal 
The author of the acclaimed The 
Dark Range takes us on a fascin- 
ating year’s visit to an Ohio ridge 
teeming with a remarkable variety 
of life. “Delightful!' — Toledo Blade 
53 pencil drawings. $12.95 
A SIERRA CLUB BOOK 
for active galactic nuclei have been 
based are: (1) a dense star cluster, 
(2) a supermassive star, and (3) the 
accretion of material onto the perim- 
eter of a black hole — a black hole 
being a concentration of mass with 
a gravity so strong as to prevent the 
escape of anything, including light. 
There are two ways in which energy 
might be generated by a dense star 
cluster at a rate far in excess of the 
rate at which energy is produced by 
the normal nuclear processes that oc- 
cur in the member stars of normal 
clusters. If the cluster is dense enough, 
collisions between its member stars 
could take place, causing the stars 
to break apart and thereby release 
energy at a rate in excess of the rate 
at which the stars normally shine. In 
such a case, the rate of energy pro- 
duction could even be far in excess 
of the rate of energy production of 
an entire galaxy of stars. 
However, a sufficiently high rate 
of energy production is not the only 
criterion that must be met in order 
to explain the activity in a quasar 
or the nucleus of a Seyfert galaxy. 
The concentration of mass must also 
be able to provide the necessary power 
for the estimated lifetime of the active 
stage. If the extreme activity that oc- 
curs in the nuclei of Seyfert galaxies 
occurs in all spiral galaxies sometime 
during the lifetime of the galaxy, then 
the percentage of Seyfert galaxies 
would be the same as the percentage 
of the time that any spiral galaxy 
spends in the active stage. Present es- 
timates indicate that about one per- 
cent of spiral galaxies are Seyfert gal- 
axies. That means that if a spiral 
galaxy does in fact live for about ten 
billion years, as we believe, the active 
stage of the galaxy lasts about one 
percent of that time, or for one hun- 
dred million years. 
In the case of dense star clusters, 
the necessary rate of energy produc- 
tion apparently would not be sustained 
for the necessary length of time. The 
cluster, continually losing energy 
through star collisions, would con- 
dense into a supermassive star or a 
black hole in a period of time shorter 
than that required to account for the 
frequency with which the galactic ac- 
tivity is observed. 
Another possibility involving dense 
star clusters that has also been ex- 
plored is the coalescence of stars due 
to collisions. In this picture, the more 
massive stars of the cluster merge into 
bigger and bigger stars by colliding 
University of California, Santa Cruz 
JOIN A WILDLANDS 
RESEARCH TEAM 
IN THE MOUNTAIN WEST 
OR CANADA 
• Wildlife Research 
• Wildlands Research 
• Wild River Research 
SUMMER, 1981 
Field Courses, 5 Units 
Phone (408) 429-2822 or write: 
WILDLANDS RESEARCH 
INSTITUTE 
University of California, Santa Cruz 
Santa Cruz, CA 95064 
Treasures 
From The Earth 
Color Portfolio of Natural 
Specimens and Catalog 
of Minerals, Display 
Stands, Books and 
Natural Jewelry, $3.00 
Dover Scientific 
Box 601 1 C Long Island City, NY 1 1 106 
^“STflRSTRUCKTTi 
Stars, moons, planets, and UFOs are pre-cut 
luminous, and will stick anywhere. 
GLOWSTARS 
Almost 100 Glowstars can turn your ceiling into 
a glittering night sky Only 10 seconds of light 
sets stars shining Stars glow for over Vi hour 
Glowstars work over and over again— time after 
time 
Educational and Fun Set up the constellations 
over your head Add moons and satellites as dis- 
covered Use rockets and space ships to create 
your own mtergalactic wars 
Twinkling Stars gradually fade as you or your 
children fall asleep Rest under your own astro- 
logical sign every night. 
Free Zodiac Star Chart with each purchase! 
Graphicus Design Studio Suite 1716 
531 Main St. Roosevelt Island NY 10044 
Check or money order enclosed for sets of 
Glowstars at $4 95 each plus 504 postage and 
handling NY residents add 8% sales tax. Allow 4 
weeks for delivery. 
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