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Moon and Spica

May 8, 2017

Different stars face different fates. The smallest will shine feebly for trillions of years — many times longer than the current age of the universe — then simply fade away. The heaviest, on the other hand, will blast themselves to bits, briefly shining brighter than billions of normal stars.

A bright star that faces such a violent end is in good view tonight. Spica stands close to the right of the Moon as night falls, with the brilliant planet Jupiter above them.

Spica actually consists of two stars.

The heavier star, Spica A, is about 10 times the mass of the Sun. Such stars burn through their nuclear fuel in a hurry. That makes them extremely bright. But it also means they won’t live long. Spica A, for example, will live a “normal” lifetime of less than 30 million years, compared to about 10 billion years for the Sun. When it can no longer produce nuclear reactions in its core, the core will collapse. The star’s outer layers will fall inward, then rebound violently, blasting the star apart as a supernova.

Its companion, Spica B, is about six times the Sun’s mass. Assuming it’s not destroyed by the nearby supernova, it’ll live more than a hundred million years. At the end of its lifetime, it’ll swell up to many times its current size, just as Spica A will. But it’s not massive enough to explode. Instead, it’ll lose its outer layers in a less-violent process. That’ll leave only its dead core, shining feebly through the long cosmic night.


Script by Damond Benningfield

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