Image of the Day: Source of a Mysterious Outburst from the Edge of the Milky Way

Hs-2003-10-i-webThis image of the variable star V838 Monocerotis near the edge of our Milky Way Galaxy, about 20,000 light-years from our sun, was recorded by the Hubble Space Telescope in September 2006.

The picture spans about 14 light-years. Ever since a sudden outburst was detected in January 2002, this enigmatic star has fascinated astronomers, who expect the expanding echoes to continue to light up the dusty environs of V838 Mon for at least the rest of the current decade. Researchers have now found that V838 Mon is likely a young binary star, but the cause of its extraordinary outburst remains a mystery.

V838 Monocerotis did not expel its outer layers. Instead, it grew enormously in size. Its surface temperature dropped to temperatures that were not much hotter than a light bulb. This behavior of ballooning to an enormous size, but not losing its outer layers, is very unusual and completely unlike an ordinary nova explosion.


The outburst 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.

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Posted by Casey Kazan. Image credit: NASA, ESA, and H. Bond (STScI)
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