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Bright Merger

February 11, 2015

For a star system in the constellation Monoceros, everything changed in a flash.

V838 Monocerotis is about 20,000 light-years away, on the rim of the Milky Way galaxy. In January of 2002, it staged a dramatic outburst — it flared a million times brighter than the Sun. It faded for a few weeks, then flared twice more.

This wasn’t like most stellar outbursts, though. It was brighter than a nova — an eruption on the surface of a small star — but not bright enough to be a supernova, which blasts a star to bits. And while novae and supernovae happen at the end of a star’s life, V838 appears to be at the start of its life.

The most popular explanation for the outburst says that a star about eight times as massive as the Sun merged with a star that was lighter than the Sun. The merger caused the outer layers of the combined stars to swell to enormous proportions — perhaps 1200 times the diameter of the Sun.

Since then, the star has been shrinking. As seen today, it’s only about 750 times the Sun’s diameter. At that size, if it took the Sun’s place in our own solar system, it would reach most of the way to the orbit of Jupiter, the fifth planet out.

The fireworks may not be over yet. V838 Monocerotis is near the lower limit of the mass required to become a supernova. If that’s the case, then millions of years from now it may blast itself apart — another dramatic change that’ll happen in a flash.


Script by Damond Benningfield, Copyright 2014

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