ROANOKE TIMES
Copyright (c) 1996, Roanoke Times
DATE: Sunday, January 21, 1996 TAG: 9601190026
SECTION: HORIZON PAGE: F-1 EDITION: METRO
DATELINE: SAN ANTONIO
SOURCE: PAUL RECER ASSOCIATED PRESS
Stars like the sun live 10 billion years and then die in a violent eruption, leaving behind an Earth-sized ember and heavenly etchings in bizarre shapes, according to astronomers who released the most detailed photos ever of this stellar process.
The sun is halfway to this final phase of its life and astronomer Howard Bond noted at a news conference last Tuesday: ``We've only got 5 billion years to get out of town.''
Bond, of the Space Telescope Science Institute, said that stars roughly the size of the sun exhaust their nuclear fuel after about 10 billion years and burst into red giants, 50 times their original size.
A core of the star then collapses, cools and becomes a white dwarf. Eventually, that fades into a black dwarf, a mere ember of its former self.
But at the beginning of its death throes, the star explosively ejects outer layers in a series of rings, rather like the concentric growth rings of a tree. These are called planetary nebulae, a name adopted centuries ago by astronomers who thought the rings resembled planets.
Some nebulae, from stars slightly larger than the sun, develop bizarre shapes, such as two overlapping circles that resemble an hour glass or lighted jets that spear the universe like the beams of a searchlight.
New photos from the Hubble Space Telescope show for the first time details of the concentric rings, and astronomers believe these rings may allow them to plot the life cycle of stars the size of the sun.
Bond said the rings were not formed in a single burst, but spewed out in episodes thousands of years apart. In the Hubble pictures, they resemble frozen ripples on a pond.
One stellar nebula, called NGC7027, is seen as a boxlike structure, with temperatures raging at 360,000 degrees at the center. Beyond, gas clouds have formed a four-pointed crest.
Another object, called the Egg Nebula, resembles a burst of light reflecting through a crystal. Concentric rings are split down the middle with a dark line and from opposite sides are bright streamers of light, which puzzled astronomers called searchlight beams.
Raghvendra Sahai of the Jet Propulsion Laboratory said the rings from the Egg Nebula are moving outward at more than 115,000 miles per hour and that a dense cloud of dust makes the dark line.
``These pictures will enable us to trace the life of these stars with fantastic accuracy,'' said Sahai. ``That has never been done before.''
``The final 10,000 years of a star's life can be studied with a clarity that we have never had before,'' said John Trauger of JPL.
Another nebula, called MyCn18, is shaped like an hourglass. Bright red overlapping rings meet at a bluish core, with a dark spot in the middle, resembling the pupil of an eye.
The violent end of life for these solar-like stars, also mark the beginning of a process that reshapes the heavens, said Trauger.
As the stars explode, they create basic elements that are recycled into new stars, planets and even life.
``This is also the rebirth of a galaxy,'' said Trauger. ``If things like this didn't happen, then the Earth wouldn't form and we wouldn't be here.''
Among the elements formed, said Bond, is carbon, the basic element of life on the Earth.
``The carbon created gets recycled back into space, and in perhaps a billion years that carbon will be recycled again, perhaps into a new planet, or into a new life,'' said Bond.
The astronomers presented studies of the new pictures at the national meeting of the American Astronomical Society.
LENGTH: Medium: 74 lines ILLUSTRATION: PHOTO: One stellar nebula, called NGC7027 (above), is seen as aby CNBboxlike structure, with temperatures raging at 360,000 degrees at
the center. Beyond, gas clouds have formed a four-pointed crest.
color.