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Stages of a star's death

The planetary nebula He 2-47 has six glowing lobes of gas, at left, leading

astronomers to nickname it the "Starfish." The nebula at right, NGC 5315, has an

X-shaped structure. Click on the images for a video about planetary nebulae.

The Hubble Space Telescope documents the beautiful stages of death for stars like our sun in a newly released series of four images.

In the first images, stars can be seen blowing away dense clouds of gas – and in the last images, those clouds have blossomed into colorful cosmic butterflies.

It wouldn't be such a pretty sight if you were right on the scene, of course. Toward the end of a sunlike star's 10 billion-year life, the hydrogen at the core runs out – and as a result, the core shrinks and heats up, while the outer layers of the star expand and cool off. The star becomes a red giant, potentially engulfing planets in its path. That's what's likely to happen to our own Earth as the sun enters its last years.

Clouds of gas puff away from the central star and are set aglow by the star's radiation. Through the small telescopes of the 18th century, the star and its surroundings would look like a fuzzy planet, leading astronomers to call the phenomenon a "planetary nebula."

The first two Hubble pictures, seen above, show young planetary nebulae just at the start of the show. The pictures aren't exactly what you'd see with the naked eye. Rather, they've been color-coded to reflect the different elements present in the gas cloud. Red stands for nitrogen, green for hydrogen, blue for oxygen.

He 2-47, at left, is youngest and has the smallest cloud, dominated by relatively cool nitrogen gas. In today's photo advisory, the Hubble team says the nebula has been nicknamed "the Starfish" because of its six-lobed shape. The shape suggests that the star puffed out gas and dust at least three times in three different directions.

NGC 5315, at right, has been percolating for a longer time. As a result, the cloud is spread out wider, with hydrogen and oxygen starting to come to the fore. The nebula's X-shaped structure suggests that the star ejected gas and dust in two opposing directions during two separate outbursts, the scientists say.

The images below show planetary nebulae at a stage perhaps thousands of years more advanced than the nebulae above.

NGC 5307 displays a spiral pattern, at left. IC 4593 has strange-looking "bullets"

stretching out from its shell, at right. Click on the image to watch a video about

planetary nebulae from the Space Telescope Science Institute.

The dynamics of the gas blown out by the central star shape extended shells – and in the process, strange-looking tails and spirals may crop up. NGC 5307, at left, displays a spiral pattern that may be due to the wobbling motion of the central star as it spewed gas like a cosmic lawn sprinkler. The enigmatic "bullets" of glowing gas that show up in the nebula IC 4593, at right, have been the subject of more than oneresearch paper over the years.

All these nebulae are in our own Milky Way galaxy, at distances of about 7,000 light-years from Earth. The snapshots were taken in February using Hubble's Wide Field and Planetary Camera 2 and presented as part of the Space Telescope Science Institute's Hubble Heritage program.

Planetary nebulae are thought to be fleeting phenomena, lasting for only 10,000 years or so before they fizzle out. Click on either of the images to launch a video from the Space Telescope Science Institute that explains more of the science behind dying stars, or click through our slide show of planetary nebulae.