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For white dwarfs, Earths for dinner: lots of rocky debris pollutes dead stars' atmospheres.

Astronomers studying the atmospheres of planet-munching white dwarf stars have found that some stellar meals include the same ingredients as Earth.

Remains of rocky bodies that once circled the white dwarfs pepper the gas envelopes around the dead stars. The ratios of elements in the remains--called "pollution," since it mars a star's pristine atmosphere--tell astronomers what the digested bodies were made of.

"We think that most of these systems that show pollution must in some way approximate ours," says astronomer John Debes of NASA's Goddard Space Flight Center in Greenbelt, Md. "This is the first hint that despite all the oddball planetary systems we see, some of them must be more like our own."

Using the Keck I telescope in Hawaii, Ben Zuckerman of UCLA and colleagues found that each of two polluted white dwarf stars snarfed at least 10 quadrillion metric tons of rocky dust. White dwarf PG1225-079 has a mix of magnesium, iron and nickel in ratios resembling Earth's; white dwarf HS2253+8023 munched material containing more than 85 percent oxygen, magnesium, silicon and iron--very much like Earth, the team reports online August 7 at arXiv. org and in an upcoming Astrophysical Journal.

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"This means that planetlike rocky material is forming at Earthlike distances or temperatures from these stars," says Zuckerman. He notes that it's still unclear whether the material is from a planet, planetlike bodies or an asteroid.

For years, astronomers thought the dwarfs were simply catching dust during their interstellar travels. Now, scientists think the debris signals ancient orbiting planetary systems. Zuckerman says that 25 to 30 percent of white dwarfs have orbital systems containing both large planets and smaller rocky bodies. After a dwarf forms, Jupiter-mass planets can perturb the orbits of smaller bodies and bounce them toward the star.

White dwarfs are about the size of Earth but as massive as the sun. They mark the final stage of stellar evolution for most stars in the Milky Way. But before reaching that stage, stars puff up into red giants, a process that can rearrange an orbiting planetary system.

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Title Annotation:Atom & Cosmos
Author:Drake, Nadia
Publication:Science News
Geographic Code:1USA
Date:Sep 24, 2011
Words:346
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