Asri-unix.1268
net.space
utzoo!decvax!cca!mclure@SRI-UNIX@sri-unix
Wed Apr 21 02:35:22 1982
Eta Carinae
!a034 0159 21 Apr 82
PM-Super Star,550
Star Explosion May Be Visible During Daytimer new grafs and SUBS
By WARREN E. LEARY
AP Science Writer
WASHINGTON (AP) - A stellar event of the highest magnitude is
imminent, say astronomers, who are predicting that the largest star in
the Milky Way could at any moment become the next supernova
observable from Earth.
The rare phenomenon, signalling a massive explosion of the giant,
swollen star, could be sighted at any time - today or 10,000 years
from now - but astronomers say it will be ''soon'' in the cosmic scale
of time.
When it does, the star will suddenly appear to be up to 100 million
times brighter than before it exploded and could be seen even in
broad daylight for a time.
Dr. Kris Davidson of the University of Minnesota in Minneapolis said
Tuesday that the star Eta Carinae appears to be the most likely
candidate in our part of the Milky Way galaxy to become a supernova.
''It may not be the next, but we can't identify another one that
will go off in the next 100,000 years,'' Davidson said in a telephone
interview.
Scientists estimate that a supernova occurs every 50 years among the
billions of stars in our galaxy. But because only about a tenth of
the galaxy is visible from the Earth, one can be observed only every
couple of hundred years.
The last supernova recorded occurred in 1604, however, so another is
long overdue.
Eta Carinae, visible only from the Southern Hemisphere, appears to
be the only star of its kind discovered in the Milky Way. It is 100
times more massive than the sun and has a diameter of about 60 million
miles, compared with less than a million miles for the sun.
''We call it a blue super giant and it really is unique,'' Davidson
said. ''There are some stars in other galaxies that look similar, and
these are among the most luminous stars there are.''
Such a star has a typical lifetime of only 2 or 3 million years,
compared with several billion years for a slower-burning body such as
the sun. The giant stars are so bright because they burn up their
hydrogen fuel at a tremendously accelerated rate, astronomers say.
Stars become supernovas when they burn up most of their fuel, swell
and then explode in a burst of light and energy.
The explosion of Eta Carinae would cause it to give off more light
than the combined brilliance of all the other stars for a period of
weeks, Davidson said. It would be visible from Earth as a bright point
of light even in the daytime.
Eta Carinae is about 9,000 light years from Earth. A light year is
the distance light travels in space in a year at 186,000 miles per
second, about six trillion miles. That means its explosion into a
supernova actually may have occurred thousands of years ago but hasn't
yet become visible here.
The star has been known to astronomers for hundreds of years. But
because a thick mass of dust and gas it previously ejected obscures
direct observation, no one knew whether it was a new star forming or
an old star dying.
Davidson and Drs . Nolan R. Walborn and Theodore R. Gull of the
Goddard Space Flight Center in Maryland made new observations using
the Cerro Tololo Inter-American Observatory in Chile and the
International Ultraviolet Explorer Satellite orbiting the Earth.
Their work, financed by the National Science Foundation and
published in the current Astrophysical Journal, determined that the
star is nearing the end of its life.
ap-ny-04-21 0459EST
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