HUBBLE PHOTOS CAPTURE LIFE CYCLE OF STARS.

Byline: Robert S. Boyd Knight-Ridder Tribune News Wire

With stunning new images from the Hubble Space Telescope, astronomers are witnessing the death and rebirth of stars - foreshadowing the inevitable doom of our own sun 5 billion years from now.

They also are learning that the universe may be littered with the corpses of burned-out stars, perhaps solving the mystery of the missing "dark matter" that has baffled scientists for decades.

Pictures presented in San Antonio on Tuesday to the American Astronomical Society reveal never-before-seen details of four "planetary nebulae," enormous shells of hot gas thrown off during a star's death throes.

Each image is strikingly different. One looks like a delicate hourglass, another a brilliant searchlight, the third a red rectangle, and the fourth a fiery coal glowing on a pale blue cushion.

"These planetary nebulae are a warning that we have 5 billion years to get out of town," quipped Howard Bond, a Hubble astronomer.

Astronomers have known for years that the sun, like most ordinary stars, has an expected life span of about 10 billion years. "We've now squandered the first half of that," Bond said.

What is new from the Hubble photographs is the astonishing detail of the actual process of star death.

Scientists can determine the age of stars by the rate at which they burn their fuel. When the sun has burned up most of its nuclear fuel, astronomers say, its inner core will collapse and its outer layer will expand 50 to 100 times. It will become a red giant, looming as far as the orbit of Jupiter and swallowing everything in its path, including the Earth.

"You wouldn't want to be around at that time," said Stephen Maran, the society's spokesman.

A red giant's end comes fast, according to Bond. After only a few thousand years, the outer layer of the dying star is blasted out into space, carrying with it iron, carbon, oxygen, nitrogen and other elements - some of them essential to life - that were created in the star's nuclear furnace.

"The star is being recycled back into space, where it may be reincorporated in a new star, a new planet and perhaps new life," Bond said.

Meanwhile, the core cools and contracts to a "white dwarf," a burned-out star about the size of the Earth. And finally, the white dwarf dwindles into a frozen cinder.

Intriguingly, this scientific story of stellar degeneration and regeneration recapitulates the cycles of birth and death contained in myth and religion.

"Like human beings, stars are born, live and die," said Raghvendra Sahai, an astronomer at the Jet Propulsion Laboratory in Pasadena, Calif.

John Trauger, an astronomer at JPL, explained, "The death of stars is how a galaxy renews itself. If that didn't happen, we wouldn't be here."

Humans will not be around to see the death of our sun, which probably will not be as spectacular as the new Hubble images would indicate.

Instead, the sun will form a "run-of-the-mill nebula, something like a beach ball," predicted Patrick Huggins, a New York University astronomer.

That is because the sun is a solitary star, lacking a nearby companion that twisted the nebulae displayed Tuesday into their fantastic shapes.