July 24, 2006

Dusty disks may slow down fast-spinning stars

WASHINGTON (Reuters) - When you're young and single, it's
easy to dance fast. But when little ones are on the way, the
dance tends to slow down. And so it seems to be with stars and
the planet-forming disks that orbit them.

Scientists have long reckoned that the disks of gas and
dust that can turn into planets might be putting the brakes on
young stars, which can spin around in half a day or less if
nothing tugs on them, researchers said on Monday.

"We knew that something must be keeping the stars' speed in
check," Luisa Rebull of NASA's Spitzer Science Center said in a
statement. "Disks were the most logical answer, but we had to
wait for Spitzer to see the disks."

The orbiting Spitzer telescope sees the cosmos through
infrared radiation, which makes it particularly good at finding
the disks that swirl around stars, because the dust in the
disks is heated by starlight and glows in infrared light.

Astronomers theorize that the disk slows the spinning star
by pulling on its magnetic fields. When these fields pass
through a dust disk, they are believed to get stuck "like a
spoon in molasses," the researchers' statement said.

Stars start out as collapsing balls of gas that spin faster
as they shrink; as they spin, excess gas and dust flattens
around them into pancake-like disks. Astronomers believe this
gas and dust eventually clumps together to form planets.

Rebull was the lead author of a paper published in the July
20 edition of the Astrophysical Journal.

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