Download From the Everett and Seattle Astronomical Societies, this is IT

February 18, 2004 - 040218.doc
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From Celestial North, this is IT'S OVER YOUR HEAD for the week of
February 18, 2004, a look at what's up in the sky over Puget Sound.
Venus grows higher and brighter this month and remains up for three hours
after sunset. Mars is steadily fading while Saturn remains a glorious sight, high
up at nightfall and reaching its nightly apex nearly overhead around 9:00 p.m.
Jupiter rises at 7:00 p.m. at midmonth and is prominent all night. The light at the
end of the tunnel is in sight. By month's end, daylight increases by three to four
minutes a day in most of the United States and four to five minutes a day in
Canada. The year's most outstanding array of stars, centered in Orion, are now
high in the sky soon after nightfall. The moon is new on February 20th.
A team of astronomers from the University of Florida may have discovered
the brightest star yet seen in the universe. This fiery behemoth could be as much
as seven times brighter than the Pistol Star, the current record holder. The Pistol
Star is named for the pistol shaped nebula surrounding it. The Pistol Star is
between 5 million and 6 million times as bright as the sun. The new brightest
star, LBV 1806-20, may be as much as 40 million times the sun's brightness.
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You won't see the star in the night sky because dust particles between the
Earth and the star block out all of its visible light. The bright star is 45,000 light
years away, on the other side of the galaxy, while our sun is a mere 8.3 light
minutes from Earth. The bright star is detectable only with instruments that
measure infrared light, which has longer wavelengths that can better penetrate
the dust.
One big problem with gauging the brightness of stars at great distances, is
that what seems at first to be one very bright star turns out on closer examination
to be a cluster of nearby stars. Astronomers have known about the LBV 1806-20
star since the 1990s. It was identified as a "luminous blue variable star" - a
relatively rare, massive and short-lived star. Such stars get their names from their
propensity to display light and color variability in the infrared spectrum.
According to Steve Eikenberry, an astronomer at the University of Florida,
luminous blue variable stars are extremely large, with LBV 1806-20 probably at
least 150 times larger than the sun. Such stars are also extremely young by
stellar time. LBV 1806-20 is estimated to be less than 2 million years old. Our
sun, by contrast, is 5 billion years old. Typical stars, such as the sun, live 10
billion years. LBVs have "short and troubled lives," as Eikenberry put it, because
"the more mass you have, the more nuclear fuel you have, the faster you burn it
up. They start blowing themselves to bits."
No one knows how LBV 1806-20 got so big. Current theories suggest such
large stars should be limited to about 120 solar masses, or 120 times as large as
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the sun, because the heat and pressure from such big stars' cores forces matter
away from the surface. Eikenberry said one possibility is that the big star was
formed in a process called shock-induced star formation, which occurs when a
supernova blows up and slams the gaseous material in a molecular cloud
together into a massive star.
The bright star is located in a small cluster of highly unusual or extremely
rare stars, including a so-called "soft gamma ray repeater," a freakishly magnetic
neutron star that is one of only four identified in the entire galaxy of 100 billion
stars. This type of star gets its name from its periodic bursts of gamma rays and
has a magnetic field hundreds of trillions of times more powerful than Earth's
magnetic field. The cluster also includes an infant or newly formed star. "We've
got this zoo of freak stars, all crammed together, really nearby, and they're all
part of the same cluster of stars," Eikenberry said. "It's really kind of weird."
Also buried within the cluster is an extremely young infant star, Eikenberry
said. The presence of the infant star, the luminous blue variable and the soft
gamma ray repeater are vivid examples of an important emerging fact about
stellar evolution: All stars in a single cluster don't form at the same time, he said.
"We're seeing what I think is going to become a textbook example of the fact that
stars aren't all born in an instant, even in a small cluster," he said.
Don Figer, an astronomer at the Baltimore-based Space Telescope Science
Institute, who was the discoverer of the Pistol Star, said the research makes an
important contribution to astronomers' understanding of the star formation
process. "The findings are significant because such massive stars are very rare
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and define the upper limits of the star formation process," he said. "The team has
made a remarkable contribution to our understanding of the most extreme stars."
We're on the web at celestialnorth.org. Until next time, this is
____________ and ____________, with a reminder that the night is very large
and full of wonders!
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February 18, 2004 - 040218.doc
REFERENCES:
http://spaceflightnow.com/news/n0401/12brighteststar/
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