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Moon, Saturn, and Spica

March 9, 2012

Most people tend to add a little weight as they age. But the opposite is true for stars. They tend to lose weight -- gradually for most of their lives, then in a big puff as they near the end.

Consider Spica, the brightest star of Virgo. It rises to the lower left of the Moon late this evening, with the planet Saturn about the same distance to the lower left of Spica.

Spica actually consists of two stars, both of which are much bigger, brighter, and heavier than the Sun.

Today, both stars are losing mass through strong “winds” -- a steady flow of hot gas from their surfaces. The winds are much denser than those from the Sun; over millions of years, the total amount of material lost will add up to the equivalent of a small star.

As they near the ends of their lives, though, both of Spica’s stars will lose much more of their mass. Over a few thousand years, the lighter of the two will shed the equivalent of about five times the mass of the Sun. For a while, this material will form a glowing cloud around all that remains of the star -- its hot, dense core.

Spica’s heavier star will create its own cloud. At the end, though, it’ll probably blast most of its remaining gas into space all at once -- in a titanic explosion known as a supernova. The leftover core will be smaller but heavier than that of its sister star. Even so, the star will have lost more than three-quarters of its original mass -- a weight-loss program seen only in the stars.


Script by Damond Benningfield, Copyright 2012


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