A Mysterious Erupting Star

A Mysterious Erupting Star

Last winter, 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 one of the latest reports to come from the Space Telescope Science Institute in Baltimore, Maryland -- the nerve center of the Hubble Space Telescope -- reported that HST had imaged a phenomenon called a "light echo" from the blast.

"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."

The star, called V838 Monocerotis (V838 Mon) is about 20,000 light-years from Earth. Apparently the star has been quite active before HST imaged it. Specifically, the star has presumably ejected shells of dust in previous outbursts. As light from the latest stellar explosion traveled away from the star into space, it smashed into these dust shells now surrounding the star. What we see is the reflection of light from that collision. Because of this indirect path, the light arrives at Earth months after light coming directly toward Earth from the star itself. Howard Bond of the Space Telescope Science Institute says 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.

And what HST has been able to do is essentially make an 'astronomical cat-scan' of the space around the star. 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.

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