HUBBLE SURVEYS DYING SUNS IN NEARBY GALAXY
08-Mar-2000
Article courtesy of
NASA and Hubble Heritage Team
From ground-based telescopes, the glowing gaseous debris surrounding
dying, sun-like stars in a nearby galaxy, called the Large Magellanic
Cloud, appear as small, shapeless dots of light. But through the
"eyes" of NASA's Hubble Space Telescope, these bright dots take on
a variety of shapes, from round- to pinwheel-shaped clouds of gas.
Using Hubble's Space Telescope Imaging Spectrograph, scientists
probed the glowing gas surrounding 27 dying suns, called planetary
nebulae, in the Large Magellanic Cloud. The observations represent
the most detailed study of planetary nebulae outside the Milky Way.
The six objects in the picture illustrate the assortment of planetary
nebulae identified in the galaxy. SMP 16, 30, and 93 are examples of
a bipolar nebula, twin lobes of gas projecting away from a dying star.
SMP 10 has a pinwheel shape and is known as a "point-symmetric" nebula.
SMP 4 has an elliptical appearance, and SMP 27, consisting of four
lobes of gas, is called a "quadrupolar" nebula. The lines point to the
objects' locations in the Large Magellanic Cloud. A ground-based
observatory snapped the picture of this galaxy.
In the pictures of the planetary nebulae, color corresponds to
temperature. Blue represents hotter regions of the nebulae and red,
cooler.
Scientists are probing these illuminated stellar relics in our
neighboring galaxy because they are at relatively the same distance -
about 168,000 light-years -- from Earth. Knowing the distance to these
objects allows scientists to compare their shapes and sizes, and
precisely determine the brightness of their central stars. For this
reason, even though these glowing remains of dying stars are about 50
times farther away than the stunning planetary nebulae photographed
in the Milky Way, they are of invaluable importance.
By sampling this population, scientists noticed that the bipolar
nebulae are richer in some heavier elements, such as neon, than those
with a more spherical shape. At the dawn of the universe, only the
lighter elements, such as hydrogen, filled the heavens. The heavier
elements were produced later as stars died. Neon, in particular, is
produced only when massive stars die in supernova explosions. Thus,
a higher abundance of neon in "bipolar" planetary nebulae indicates
that the stars that sculpted these objects were born more recently
(i.e., in an environment that had suffered more supernova explosions)
than those that created the more symmetrically shaped clouds of gas.
On the other hand, the stars that form planetary nebulae are great
producers of carbon, the most important element for the origin of
life, as we know it. The question of how life-forming atoms were
made is at the heart of understanding how and why life evolved in
our own solar system very shortly after the Sun itself had formed
from clouds of carbon-enriched gas and dust 4.6 billion years ago.
Scientists do not know for sure how the Milky Way behaved before
the birth of the Sun. But they can look at regions in other galaxies
where conditions may be very similar to the pre-solar days of the
Milky Way. The Large Magellanic Cloud is an ideal laboratory for such
an experiment, since its chemistry mimics a pre-solar environment.
Astronomers are using the Hubble images of these planetary nebulae,
together with spectroscopic information from ground-based
observatories, to understand the important carbon-forming mechanisms
in the Large Magellanic Cloud. The progenitor stars are expected to
form some carbon and lock it deep in their interiors near the end
of their lives. In the last few thousand years of their active
lives, just before ejecting planetary nebulae, stars are able to
dredge up the carbon locked deep in their cores. They undergo a
phase as "carbon stars," then fling the carbon-rich gas into space
as they form planetary nebulae, material for new generations of
stars and planets.
The Hubble images were taken between June and September 1999.
Credits for the Hubble images: NASA; L. Stanghellini, R. Shaw,
C. Blades, and M. Mutchler, Space Telescope Science Institute,
Baltimore, Md.; and B. Balick, University of Washington, Seattle, Wash.
Credits for the copyrighted image of the Large Magellanic Cloud:
D. Malin, Anglo-Australian Observatory/Royal Observatory, Edinburgh,
Scotland
Images are available on the Internet at:
http://oposite.stsci.edu/pubinfo/pr/2000/09 and via links in
http://oposite.stsci.edu/pubinfo/latest.html and
http://oposite.stsci.edu/pubinfo/pictures.html
Higher resolution digital versions (300 dpi JPEG and TIFF) are
available at:
http://oposite.stsci.edu/pubinfo/pr/2000/09/pr-photos.html and
http://oposite.stsci.edu/pubinfo/pr/2000/09/extra-photos.html
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