Using the
largest telescopes available, astronomers have dissected the dusty, gassy layers
of the red giant S Orionis--a star that pulsates in size from a diameter roughly
equal to the orbit of Mars to halfway between Mars and Jupiter every 410 days.
The
information provides a glimpse at the future
of our own sun, which will puff into a red giant like S Orionis in about 5
billion years, said astronomer David Boboltz of the U.S. Naval Observatory.
"No study
of a red giant has been done to this level, looking at infrared and radio-wave
views simultaneously," Boboltz said. "This really show us where the layers
are."
Giant
mystery
Red
giants are older versions of the sun that, once they have burned off most
of their hydrogen fuel, begin to burn helium. This creates intense "flashes" of
radiation that puff the star up to more than 100 times its original size as it
pushes stellar gas and dust out into space. S Orionis sheds about the mass of
Earth each year.
"A lot of
material escapes from the star's gravity, and begins to form beautiful planetary
nebulas," Boboltz said. "But gravity overcomes a lot of gas and dust that
gets pulled back into the star, starting the cycle all over again and forming a
kind of pulse."
Where those
layers are located and exactly what they're made of, however, was a mystery
until Boboltz and his colleagues' investigation, which is detailed in a July issue
of the journal Astronomy & Astrophysics.
The team
measured the shells of gas and dust surrounding the star to most detailed level
to date, discovering that the star's dusty shell of corundum--a compound used in
sandpaper--was twice as large as previously thought. They also showed dusty
corundum mixing heavily with gaseous silicon monoxide, a compound
astrophysicists thought existed as a dust outside of red giants.
"We've
essentially mapped the envelopes of material around these stars, which has
never really been done before," Boboltz said.
Big
investigation
The
researchers aimed two of Earth's biggest interferometer
telescopes at the star to peer at its layers: the Very Long Baseline Array
(VLBA), a series of 10 telescopes spread over 5,350 miles that can see radio
waves, and the infrared-seeing Very Large Telescope Interferometer (VLTI) in Chile.
If the
telescopes were in New York, Boboltz noted, they would allow someone to read a
newspaper in California. But regular sources of radio and infrared waves would
make S Orionis look more like "a blob of emissions," so his team recorded its "masers,"
or naturally occurring lasers.
Astrophysicists
aren't entirely sure how they form, but the basic principles of a laser apply:
Some process evenly energizes one kind of molecule to produce a "synchronized"
wave of light.
"Stuff like
corundum and silicon monoxide, which we detected in S Orionis, emit their own
unique masers," Boboltz said. By watching the masers move over the period of a
few months, they recorded an extremely detailed picture of the red giant's
pulsating behavior.
A video
exists of another pulsating red giant star, call TX Cam, but Boboltz
expects to surpass it's a visualization of only radio images.
"Soon we'll
be able to create even better views of the pulsating cocoon around S Orionis by looking at water masers," Boboltz said, which exist at the farthest reaches of
the cocoon. "We also hope to explain how a planetary
nebula forms from a red giant near the end of its life as a white
dwarf star."
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