Sirius and Procyon are two of the brightest and closest stars in the night sky. And by coincidence, they both have faint companions. These companion stars are destined to become black dwarfs -- stars that have faded to invisibility.
Today, the companions to Sirius and Procyon are classified as white dwarfs. They're only about as big as Earth, but they still shine because they're very hot.
This heat is left over from the white dwarf's earlier life, when it shone as the Sun does -- by generating energy from nuclear reactions in its core. But the star ran out of fuel and cast its outer layers into space. All that remains today is the dead core -- a star so dense that a spoonful weighs more than a ton.
As white dwarfs shine their meager light into space, they cool, so they fade even more. Countless trillions of years from now, the stars will have faded completely, so they'll be black dwarfs.
Right now, though, there's not a single black dwarf anywhere in the universe. That's because the universe isn't old enough for any white dwarfs to have had enough time to cool and fade away. Come back in the far-distant future, though, and the white dwarfs around Sirius and Procyon will have faded to black.
Look for Sirius well up in the southeast in early evening. It's the brightest star in the night sky. Procyon is far to its left, and a little higher. Their companions are visible through telescopes -- and will stay visible for a long, long time.
Script by Damond Benningfield, Copyright 2007
For more skywatching tips, astronomy news, and much more, read StarDate magazine.
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