Star Death, With Style

Stellar example. The planetary nebula M2-9 is a type of nebula called a "bipolar" nebula, with twin jets of material ejected from both sides of the parent star.

Striking new photos from the Hubble Space Telescope are giving astronomers insights into the deaths of ordinary stars like our sun. The images, released yesterday at a news conference at NASA headquarters, depict a star's demise as unexpectedly complex and beautiful. They also foretell, more vividly than ever before, the fate of our own solar system some 5 billion years from now.

The Hubble snapped portraits of several elegant glowing objects called "planetary nebulae," so named because their discoverers in the 18th century thought they resembled planets. The nebulae form when midsized stars run out of fuel and belch their outer layers, leaving behind superheated white dwarfs. Ultraviolet radiation from the dwarf's surface ionizes the expanding shells of gas, creating colorful "sculptures in the sky," says astronomer Mario Livio of the Space Telescope Science Institute in Baltimore.

When Livio and his colleagues zoomed in on several planetary nebulae with the Hubble--whose images have 10 times more resolution than earlier ones--they were startled to find such intricate patterns. Several nebulae had "jets" of material streaming away at high speeds, a far cry from the leisurely expanding globes of gas that astronomers had expected. Other nebulae were rounder, but contained symmetrical patterns of dense knots and blobs of gas. Livio suggests that stellar companions--such as other stars in close orbit, brown dwarfs, or large planets--can speed up the rotation of the dying stars, forcing them to eject their outer layers in certain directions.

The new details may also help scientists better understand the other end of the stellar life cycle: star birth. Elements shed from dying stars give rise to new stars, planets, and--perhaps--life. Planetary nebulae, which, along with supernovae, provide the raw stuff of future star formation, are "fantastic laboratories in space for atomic physics research," says astronomer Yervant Terzian of Cornell University. He points out that in the distant future, our sun--the archetypal regular star--is expected to cast off its own planetary nebula after engulfing and incinerating Earth. Since the sun is a cosmic loner, its nebula probably will be spherical.

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