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The Dog’s Tail

January 12, 2016

The hindquarters of the big celestial dog face a painful future. The stars that outline the tail and back legs of Canis Major, the big dog, are destined to explode within the next few million years.

Canis Major clears the southeastern horizon by about 9 o’clock. It contains the brightest star in all the night sky, Sirius, at the front of the dog. The hindquarters are outlined by a triangle of three moderately bright stars well below Sirius: Wezen at the top of the triangle, Adhara to its right or lower right, and Aludra, the faintest of the three, at the bottom.

The three stars are quite similar. They’re all much bigger, brighter, and hotter than the Sun, and more than 10 times heavier. And they’re all in about the same stage of life. They’ve used up the hydrogen fuel in their cores, so the nuclear reactions in their cores have stopped. Now, the cores are shrinking and getting hotter, so they’re about to ignite the next round of reactions, fusing helium to make carbon and oxygen. When that happens, the stars will get even bigger and brighter.

And all three stars likely face the same fate. Within a few million years, they’ll all reach a point where they can no longer sustain nuclear reactions. When that happens, each star’s core will collapse, and its outer layers probably will explode as a supernova.

Although it looks fainter than the other two, the most impressive of the three stars appears to be Aludra, at the tip of the dog’s tail. More about that tomorrow.


Script by Damond Benningfield, Copyright 2015

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