Using Hubble's Space Telescope Imaging Spectrograph, scientists probed the glowing gas surrounding 27 dying stars, 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
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