This Echo is READ ONLY !   NO Un-Authorized Messages Please!
 ~~~~~~~~~~~~~~~~~~~~~~~~   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Donald Savage
NASA Headquarters, Washington                March 26, 2003
(Phone: 202/358-1547)

Lars Lindberg Christensen
Hubble European Space Agency Information Center,
Garching, Germany
(Phone: 011/49-89-3200-6306)

Ray Villard
Space Telescope Science Institute, Baltimore
(Phone: 410/338-4514)

RELEASE: 03-116

HUBBLE WATCHES LIGHT FROM MYSTERIOUS ERUPTING STAR 
REVERBERATE THROUGH SPACE

     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's Space Telescope of a 
phenomenon called a "light echo" has 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 
tomorrow 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 also do an 'astronomical catscan' 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 the Earth. Bond predicts 
that the echo will be observable for the rest of this decade.

Electronic image files and additional information are 
available at 
http://hubblesite.org/news/2003/10

The Space Telescope Science Institute (STScI) is operated by 
the Association of Universities for Research in Astronomy, 
Inc. (AURA), for NASA, under contract with the Goddard Space 
Flight Center, Greenbelt, Md. The Hubble Space Telescope is a 
project of international cooperation between NASA and the 
European Space Agency (ESA).

-end-

                            * * *

 - END OF FILE -
==========

@Message posted automagically by IMTHINGS POST 1.30
---