StarDate: May 31, 2009

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A star that's moving into the final stages of life arcs high across the south tonight. Although the star is bigger and heavier than the Sun, its fate is the same: It'll end its life as a superhot cosmic cinder called a white dwarf.

The star is Rasalhague, the brightest star in Ophiuchus, the serpent bearer. It's low in the east as darkness falls, and climbs high across the south during the night.

Like many stars, Rasalhague is actually a binary -- two stars that are bound to each other by gravity. But only one of the stars is visible to the unaided eye. This star is more than twice as massive as the Sun, and about 25 times brighter. Its surface is much hotter than the Sun's, too.

From its size, its brightness, and its temperature, astronomers deduce that the star is moving into the penultimate phase of its life: It's becoming a giant. The star has consumed the hydrogen fuel in its core, so the core is shrinking and getting hotter. That will allow it to begin burning heavier helium atoms. At the same time, the star's outer layers are puffing up, making the star much bigger.

Rasalhague will undergo a series of changes during its giant phase. Eventually, it'll cast its outer layers into space, leaving only its dense core -- a white dwarf. It will no longer produce energy, but it'll continue to shine because it's extremely hot.

The Sun is destined to undergo this same series of changes -- in several billion years.

Script by Damond Benningfield, Copyright 2003, 2009

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