A planet (right) orbits close to Alpha Centauri B, the second-largest star of the triple Alpha Centauri system, in this artist's concept. The most massive star of the system, Alpha Centauri A, is at lower left. (The third star, Proxima Centauri, is out of view.) The bright star at top right is the Sun. Alpha Centauri is the closest star system to our own, at a distance of just 4.3 light-years. [ESO/L. Calçada/Nick Risinger]
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The key to a star’s appearance and lifespan is its mass. Heavier stars shine brighter but live shorter lives than less-massive ones.
An example can be seen in the two bright stars of Alpha Centauri, the leading light of the constellation Centaurus. It’s the closest star system to our own, at a distance of four light-years.
One of the stars is about 10 percent more massive than the Sun, while the other is about 10 percent less massive than the Sun. With so little difference, you might expect them to be almost identical, but they’re not.
The heavier star, Alpha Centauri A, burns through the nuclear fuel in its core faster than its companion, Alpha Centauri B. As a result, it shines three times brighter. The surface of Alpha Centauri A is also hundreds of degrees hotter, so it looks yellow-white versus the yellow-orange of Alpha Centauri B.
While “A” is far brighter, “B” has a much longer future to look forward to. Its “normal” lifetime should last about half again as long as that of its flashier companion.
There’s actually a third star in the Alpha Centauri system — Proxima Centauri — that’s a long way from the other two. It’s a more extreme example of what a difference mass can make. It’s only 15 percent as massive as the Sun. As a result, it’s only about one thousandth as bright as the Sun. Yet it will still be shining more than a trillion years after the other two stars have faded into the cosmic night.
More about Centaurus tomorrow.
Script by Damond Benningfield, Copyright 2015