ROANOKE TIMES
Copyright (c) 1996, Roanoke Times
DATE: Thursday, February 1, 1996 TAG: 9602010095
SECTION: NATIONAL/INTERNATIONAL PAGE: A-9 EDITION: METRO
DATELINE: SAN ANTONIO
SOURCE: GUY WEBSTER THE ARIZONA REPUBLIC
IT WILL SWELL to 50 times its size and scorch Earth. But it shouldn't happen for another 5 billion years.
In case you missed the long-term forecast: The sun's death throes will fry all life on Earth and boil away the oceans about 5 billion years from now.
Astronomers recently reaffirmed that fate and gleaned new details from the best-yet pictures of how a star like the sun goes poof.
Two of the new images from the Hubble Space Telescope are the first to show concentric shells of gas blown out by dying stars.
``These are almost like tree rings,'' said John Trauger of the Jet Propulsion Laboratory in Pasadena, Calif., one of the astronomers who took the pictures.
``The last 10,000 years of the star's history are written out with clarity we have not seen before,'' said John Trauger of the Jet Propulsion Laboratory in Pasadena, Calif.
The concentric shells and other details revealed in the images are clues to what makes stars balloon into misleadingly named ``planetary nebulae,'' said astronomer Howard Bond of the Space Telescope Science Institute in Baltimore.
Bond heads one of several research groups at the annual meeting of the American Astronomical Society reporting new findings about planetary nebulae.
They got their name more than 100 years ago when astronomers thought their roundish shapes resembled distant planets.
It takes a star much bigger than the sun to perish as a more dramatic supernova explosion, rather than a planetary nebula.
When a star the size of the sun is about 10 billion years old, it has used most of its fuel and goes through dramatic changes, said astronomer George Jacoby of Kitt Peak National Observatory.
First, it swells to about 50 to 100 times its earlier diameter, becoming a red giant for about 100 million years.
For the sun, that expansion likely will swallow Mercury and Venus entirely, but leave a scorched, lifeless Earth still orbiting, according to the most-accepted calculations.
Then, for a relative blink of about 1,000 years or less, the star becomes a planetary nebula.
The cloud expands faster than 100,000 mph, reaching thousands of times farther than the distance from the sun to the Earth, then shrinks into a slowly fading and cooling white dwarf, Jacoby said.
``These planetary nebulae are warning that we have 5 billion years to get out of town,'' Bond said.
LENGTH: Medium: 54 linesby CNB