Image of the Day: Massive Outburst at the Edge of the Milky Way

200880main_rs_image_feature_877_9_3 This stunning image of swirls of dust surrounding 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.

In January 2002, what was 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, V838 Monocerotis, has long since faded back to obscurity. But observations by NASA's Hubble Space Telescope of a phenomenon called a "light echo" around the star 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 picture above 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 (see image below). 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.


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


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