Re: News: Puzzle of Hot Young Stars Solved.

Ye Old One wrote:
Puzzle of Hot Young Stars Solved

http://news.yahoo.com/s/space/20070814/sc_space/puzzleofhotyoungstarssolved;_ylt=At0z_AolvTJNHn1Vw.wr65OFDvII
Dave Mosher
Staff Writer
SPACE.com Tue Aug 14, 6:15 AM ET

Most newborn stars are gluttons, feeding on afterbirth of dust and gas
long after igniting.

Although this accreting activity doubles stellar surface temperatures
by burning up the material, it mysteriously softens the emission of
high-energy X-rays.

"Accreting stars have three times less X-ray emission than
non-accreting stars, which seems unusual," said Kevin Briggs, an
astrophysicist at the Swiss Federal Institute of Technology in Zurich,
Switzerland.

Now Briggs and several teams of researchers have discovered why some
stars' X-ray profiles are so thin: The nebulous surroundings of a
young star absorb the extra energy produced by falling into it.

The discovery gives astronomers a better glimpse into the early stages
of stellar life.

Burning filters

Briggs explained that dust and gas surrounding young stars act like
light filters on a camera, where gas absorbs X-rays and dust absorbs
visible light.

Yet if both materials surrounding energetic young stars are very
dense-and soak up most of the energy they create-Briggs said the team
wondered why the stars weren't fainter.

The filters, it turns out, burn.

"The dust is heated so much by the radiation from the star, that it is
vaporized before it can fall on the star," said Manuel Guedel, also an
astrophysicist at the Swiss Federal Institute of Technology.

As the dust and gas still waiting to be eaten by the young stars
vaporizes, Briggs explained, they glow like hot plasma and mimic the
appearance of a star's surface.

Shocking creation

Briggs said repetitive "shocks" of energy create young stars' X-rays,
and that there are two recipes to make them.

The first type of shock is produced when gas and dust falls into a
star and slams into its surface at nearly one-tenth the speed of
light, or about 671,000 mph (1,080,000 kph). "The impact against the
star's surface can produce the high-energy shock," Briggs said.

The second type of X-ray shock in young stars is produced by gas and
dust jettisoned away from a star's poles.

"It happens when fast-moving material catches up to slow-moving
material and collides," Briggs said. But nature leans toward variety
with its shocking young stars. "What we actually see is both types in
these stars," he said.

Because stellar meals of gas and dust absorb most young stars' X-ray
outputs, the teams think the few X-rays that can be detected originate
from shocks emitted from the stars' jets.

"This emission must come from outside the accretion streams," Guedel
said. The teams looked at 400 young stars in the constellation Taurus
to uncover their findings, which are detailed in a recent issue of the
journal Astronomy and Astrophysics.

It's good to see this wasn't spam about Paris Hilton.

--Jeff

--
"Every gun that is made, every warship launched,
every rocket fired, signifies in the final sense
a theft from those who hunger and are not fed,
those who are cold and are not clothed."
--Dwight Eisenhower

.

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