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95_27.txt
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1996-01-12
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FOR RELEASE: 2:00 PM EDT, TUESDAY, JUNE 13, 1993
PRESS RELEASE NO.: STScI-PR95-27
HEAVIEST STAR KNOWN OBSERVED FROM SPACE
Observations with the Hopkins Ultraviolet Telescope (HUT) of the most
massive star currently known have revealed new features of its hot
outer layers, which are being blown away from the star at speeds of up
to 2300 miles per second due to its extreme luminous energy output.
These features in turn provide information about physical
characteristics of the star, such as its temperature, luminosity,
chemical composition, age, and mass, or total amount of matter it
contains.
The results were presented today at the meeting of the American
Astronomical Society in Pittsburgh, PA. An international collaboration
consisting of Drs. Nolan R. Walborn and Knox S. Long from the Space
Telescope Science Institute in Baltimore, MD, and Drs. Rolf-Peter
Kudritzki and Daniel J. Lennon from Munich University, Germany, reported
observations of the stellar record holder with the Hopkins Ultraviolet
Telescope, which was operated from the space shuttle Endeavour last March.
The HUT data show previously unseen features of the "stellar wind" of
HDE 269810 in the Large Magellanic Cloud (LMC).
Analysis of earlier data from the Hubble Space Telescope (HST) and the
European Southern Observatory in Chile indicates that this star may be
190 times as massive as our Sun, the largest value to date. Its parent
stellar system or galaxy, the LMC, is a relatively small satellite of our
giant Milky Way Galaxy, at a distance of 170,000 light-years from us. (A
light-year is the distance which light travels in one year at a speed of
186,000 miles per second, or about 6 trillion miles.)
The Hopkins Ultraviolet Telescope is able to probe shorter ultraviolet
wavelengths of light than the HST, and so it can observe spectral
features not accessible to previous instruments. For instance, one of
these features is produced by oxygen atoms from which five electrons
have been removed; it is formed in very-high-temperature regions of the
star's expanding outer layers. This expansion ejects the material from
the star and it is governed by the star's mass, luminosity, and other
parameters, which can be derived from the observations. Further analysis
of the newly observed features will refine and confirm the extreme
characteristics of HDE 269810.
Massive stars have relatively short lifetimes, only a few million
years compared to ten billion years for the Sun, because they burn
their nuclear fuel more rapidly. They are very important components
of the Universe, however, because their nuclear reactions synthesize
most of the heavier chemical elements such as the iron in our bridges
and our blood. These newly made elements are blasted out into space
in the violent supernova explosions with which massive stars end their
lives, and they mix with other interstellar material which may form new
generations of stars. The material which makes up the Sun and Earth
has been enriched with heavy elements made in massive stars which lived
and died before our solar system formed.
Because of the large distance of the LMC, it is likely that some massive
stars we observe there today have already exploded, but the events are
still on the way to us across the intervening distance at the speed of
light. The nearest supernova to us seen since the invention of the
telescope was observed in the LMC in 1987; of course, the event actually
occurred there 170,000 years earlier. The initial mass of the Supernova
1987A progenitor star was only 20 times that of the Sun. Perhaps HDE
269810 will have an even more spectacular demise, although some theories
suggest that a star of such extreme mass may collapse completely into
a black hole and simply disappear from sight when its nuclear fuel is
exhausted, without any accompanying outburst of light and matter.
This work was supported by the National Aeronautics and Space
Administration.
For more information, contact Dr. Nolan R. Walborn (410-338-4915).