Sirius B

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Today, the Sun is big and bright. But it will end its days as a white dwarf -- a dense ball that's only about as big as Earth, and a tiny fraction as bright as the present-day Sun. That won't happen for several billion years. But many other stars have already suffered this fate. And the nearest one is less than nine light-years away.

The star is a companion to Sirius, the brightest star in the night sky. Sirius is well up in the southeast at nightfall, and rolls across the south during the night.

In 1844, astronomers noticed that Sirius wasn't moving through space in a straight line. Instead, it was wobbling, as if something were tugging it from side to side. Astronomers found this mysterious "something" in 1862 -- a faint companion known as Sirius B.

Sirius B is as massive as the Sun, but less than one percent as bright. It was once the core of a star that was bigger and more massive than the Sun. But the star used up its nuclear fuel and shed its outer layers. All that remains is the shrunken corpse -- a white dwarf. It shines simply because it's still hot.

Even though Sirius is quite close, Sirius B is so faint that you need a telescope to see it. And its future is even darker. Over billions of years, it'll cool and fade more -- eventually becoming a black dwarf. We'll have more about that tomorrow.

Script by Ken Croswell, Copyright 2007

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