Nebulous 'Spirograph' astounds Hubble astronomers

larger   The Spirograph Nebula

By Richard Stenger
CNN.com Writer

(CNN) -- A young nebula offers a brilliant display of textures and colors, but its shape mystifies astronomers who have used the Hubble Space Telescope to take clear pictures of the once sun-like star.

Hubble scientists snapped the picture of the Spirograph Nebula while conducting a survey of planetary nebulas, a celestial census that could shed light on the fate of our sun.

When ordinary stars like our sun enter their twilight years, they swell into red giants and then cast off their outer layers, ghostly halos of gas and matter. The death shrouds expand and glow, heated by ultraviolet radiation from the hot core of the dying stars.

A nebula will expand for several millennia. Then, over billions of years, the corpse of the interior star will gradually fade and cool into a white dwarf.

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Astronomers using ground-based telescopes thought that the nebula had an elliptical shape, said Raghvendra Sahai, the lead Hubble researcher studying the nebula. But the more powerful Hubble lens revealed that it instead exhibited a more eccentric type of symmetry.

"The central symmetry is like an 'S' shape. A point has a corresponding point on the opposite side, but not in a mirror image," said Sahai, a physicist at NASA's Jet Propulsion Laboratory in Pasadena, California.

Sahai and others theorize that bipolar jets sprinkling out material from dying stars are responsible for planetary nebulas, so called because 18th century astronomers using small telescopes thought they resembled distant planets.

In this example, 2,000 light years away in the direction of the constellation Lepus, the jets seem to fire in one direction for awhile and then change direction.

"We don't know why. It is a mystery," Sahai said.

Astronomers have enlisted Hubble to search the heavens for young nebulae, at most thousands of years old, which display greater size and shape diversity than their older brethren, Sahai said.

Hubble has spotted about 50 of them, and astronomers hope the orbiting telescope can be enlisted to find hundreds more.

The cosmic catalog could offer clues about how nebulae form, offering scientists a chance to compare theoretical models with a "mixed bag of masses and sizes" from direct observations, Sahai said.

The Spirograph image, released last week, shows a color-enhanced spectrum of heated elements. Red trace emissions from comparatively cool ionized nitrogen, green from warmer hydrogen and blue from super-hot ionized oxygen.

The sun is expected to experience a similarly nebulous fate, but not for some 5 billion years.

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Hubble images of young planetary nebulae
More planetary nebulae pictures obtained with Hubble
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