Sirius B

StarDate: January 9, 2009

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Imagine a star that's 200,000 times denser than lead. This star is slightly smaller than Earth, but as massive as the Sun. And because of its enormous gravity, a 200-pound man standing on the star's surface would weigh nearly 40,000 tons. And if he dropped a pebble from a height of three feet, the star's gravity would pull it so hard that it would crash into the surface at 6,000 miles an hour.

This extraordinary star isn't imaginary, though. It's just 8.6 light-years away -- a companion to Sirius, the brightest star in the night sky.

This dense companion is known as Sirius B. It's an exotic type of star called a white dwarf. It was once much like Sirius and the Sun. It generated heat and light through nuclear reactions in its core. But as it aged those reactions shut down. The star expanded and cooled, then cast its outer layers into space. All that's left of the star is the hot, dense core -- a small, faint stellar ember that's slowly cooling and fading from sight.

You can easily see Sirius at this time of year -- but not Sirius B. Sirius is the brightest star in the night sky, so it's easily visible even from light-polluted cities. It rises in the southeast not long after darkness falls, and climbs across the southern sky later on. Sirius B is far too faint to see without a telescope. But it continues to orbit its brilliant sibling -- the small, dense corpse of a star less than nine light-years away.

Script by Ken Croswell, Copyright 2008

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