Hubble Watches Light From Mysterious Star Reverberate
http://www.spacedaily.com/news/spaceart-03a.html
Baltimore - Mar 28, 2003
In January 2002, a dull star in an obscure
constellation suddenly became 600,000 times more
luminous than our Sun, temporarily making it the
brightest star in our Milky Way galaxy.
The mysterious star has long since faded back to
obscurity, but observations by NASA's Hubble Space
Telescope of a phenomenon called a "light echo" have
uncovered remarkable new features. These details
promise to provide astronomers with a CAT-scan-like
probe of the three-dimensional structure of shells of
dust surrounding an aging star.
The results appear this week in the journal Nature.
"Like some past celebrities, this star had its 15
minutes of fame," says Anne Kinney, director of NASA's
Astronomy and Physics program, Headquarters,
Washington. "But its legacy continues as it unveils an
eerie light show in space. Thankfully, NASA's Hubble
has a front row seat to this unique event in our
galaxy."
Light from a stellar explosion echoing off
circumstellar dust in our Milky Way galaxy was last
seen in 1936, long before Hubble was available to
study the tidal wave of light and reveal the
netherworld of dusty black interstellar space.
"As light from the outburst continues to reflect off
the dust surrounding the star, we view continuously
changing cross-sections of the dust envelope. Hubble's
view is so sharp that we can do an 'astronomical
cat-scan' of the space around the star," says the lead
observer, astronomer Howard Bond of the Space
Telescope Science Institute in Baltimore.
Bond and his team used the Hubble images to determine
that the petulant star, called V838 Monocerotis (V838
Mon) is about 20,000 light-years from Earth. The star
put out enough energy in a brief flash to illuminate
surrounding dust, like a spelunker taking a flash
picture of the walls of an undiscovered cavern.
The star presumably ejected the illuminated dust
shells in previous outbursts. Light from the latest
outburst travels to the dust and then is reflected to
Earth. Because of this indirect path, the light
arrives at Earth months after light coming directly
toward Earth from the star itself.
The outburst of V838 Mon was somewhat similar to that
of a nova, a more common stellar outburst. A typical
nova is a normal star that dumps hydrogen onto a
compact white-dwarf companion star.
The hydrogen piles up until it spontaneously explodes
by nuclear fusion -- like a titanic hydrogen bomb.
This exposes a searing stellar core, which has a
temperature of hundreds of thousands of degrees
Fahrenheit.
By contrast, however, V838 Mon did not expel its outer
layers. Instead, it grew enormously in size, with its
surface temperature dropping to temperatures not much
hotter than a light bulb. This behavior of ballooning
to an immense size, but not losing its outer layers,
is very unusual and completely unlike an ordinary nova
explosion.
"We are having a hard time understanding this
outburst, which has shown a behavior that is not
predicted by present theories of nova outbursts," says
Bond. "It may represent a rare combination of stellar
properties that we have not seen before."
The star is so unique it may represent a transitory
stage in a star's evolution that is rarely seen. The
star has some similarities to highly unstable aging
stars called eruptive variables, which suddenly and
unpredictably increase in brightness.
The circular light-echo feature has now expanded to
twice the angular size of Jupiter on the sky.
Astronomers expect it to continue expanding as
reflected light from farther out in the dust envelope
finally arrives at Earth. Bond predicts that the echo
will be observable for the rest of this decade.
The research team included investigators from the
Space Telescope Institute in Baltimore; the
Universities Space Research Association at the U.S.
Naval Observatory in Flagstaff, Ariz.; the European
Space Agency; Arizona State University; the Large
Binocular Telescope Observatory at the University of
Arizona at Tucson; the Isaac Newton Group of
Telescopes in Spain's Canary Islands; and the
INAF-Osservatorio Astronomico di Padova in Asiago,
Italy.
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John D. Giorgis - [EMAIL PROTECTED]
Tonight I have a message for the brave and oppressed people of Iraq:
Your enemy is not surrounding your country — your enemy is ruling your
country. And the day he and his regime are removed from power will be
the day of your liberation." -George W. Bush 1/29/03
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