Dying star previews a vaporized Earth


Some say the world will end in ice.

University of Maryland astronomer J. Patrick Harrington says fire. He recently photographed the red-hot death throes of a "nearby" star, using the Hubble Space Telescope, and says the image looks a lot like the cataclysm in our own sun that will one day vaporize the Earth.

That blast -- billions of years from now, according to generally accepted theory -- "will be the end of our solar system as we know it," said Dr. Harrington, a professor of astronomy.

Dr. Harrington and Dr. Kazik Borkowski, a former research scientist at College Park now with the Goddard Space Flight Center, presented the photograph yesterday at the 185th meeting of the American Astronomical Society, in Tucson, Ariz.

The dying star in the picture is a favorite of amateur astronomers. It is called the "Cat's Eye Nebula" and is also known by its more formal designation, NGC 6543. Situated in our own Milky Way Galaxy, it can be found in the northern constellation Draco, the dragon.

Astronomers believe it is about 3,000 light-years from Earth, which means the light captured by the space telescope left the star 3,000 years ago. A light-year is equal to about 5.8 trillion miles.

The photo, taken in September, shows never-before-seen detail in the glowing red gas cloud ejected by the dying star. "I think this is going to become one of the standard pictures for illustrating planetary nebulae. It's going to find its way into many textbooks," Dr. Harrington said.

A "planetary nebula" has nothing to do with planets. It is actually the expanding cloud of gas blown away from a dying star after it depletes its hydrogen fuel.

Average-sized stars like our sun and NGC 6543 "live quietly for billions of years," Dr. Harrington said. "But when it finally runs out of hydrogen in the inner part of its structure, it goes through a series of changes, and the outer layers swell up, and it becomes a 'red giant.' "

When our sun becomes a red giant, perhaps 5 billion years from now, he said, the surface of the sun ultimately will expand outward, "certainly past the orbit of Venus, perhaps to Earth's. At that stage, the inner planetary system would be vaporized."

A red giant next begins to pulsate, and finally throws off its outer layers of gas, which consist mainly of lighter elements like hydrogen and helium. As those gases race away from the star, the remaining, heavier elements collapse into a hot, densely packed, Earth-sized object called a "white dwarf," composed mostly of elements like carbon, oxygen and nitrogen.

The Hubble photograph of NGC 6543 shows the gas cloud as it existed about 1,000 years after the initial explosion. In that time, it had expanded to a diameter about 200 times that of our solar system. Glowing white like an ember at the center is the remnant star. Ultraviolet radiation from the hot white dwarf is what causes the gas to glow red.

What's remarkable about the image, Dr. Harrington said, is the detail revealed in the structure of the expanding gas.

"The features we see in this one, if not the most complicated, then are among the most complicated ever seen in nebulas," he said. "We used to think of planetaries as a single bubble of gas. Now we realize there must be a whole series of ejections [of gas] to make these complicated structures."

In addition to several "shells" of expanding gas, which appear a bit like petals of a red flower, two jets of gas are visible at opposite ends of the nebula as well as strange clumps of material moving through the gas.

Given that sort of complexity, Dr. Harrington and Dr. Borkowski suspect that NGC 6543 may actually be a double star. "It's difficult to see how an isolated star can do anything like that. With two stars, there is more latitude to work with."

The interaction of gas being thrown off by the more massive, dying star, and the gravitation of a second star nearby, Dr. Harrington said, could create jets of gas that spray material through the expanding nebula like water from a loose garden hose. The jets may also compress some of the gas and form the odd "clumps" visible in the image.

"This photograph is a clue to really understanding what these things are," he said.

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