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April 24, 2011

Neighbors can be messy. Not only can they clutter up their own yards, sometimes they dump stuff in yours, too.

That's what happened with a star named Alphard. It's the brightest star of Hydra, the water snake, which wriggles most of the way across the southern sky as darkness falls on spring evenings.

The star is nearing the end of its life, so it's puffed up to many times the size of the Sun. Eventually, it'll shed its outer layers of gas, leaving behind only its hot, dense core -- a white dwarf.

A companion to Alphard has already done just that. The star was more massive than Alphard, so it lived a shorter life. It's already lost its outer layers, so only the white dwarf survives.

As the star was dying, it dumped some of its gas onto the surface of Alphard. This gas was "polluted" with the products of several hundred million years of nuclear reactions -- heavier elements forged from the original hydrogen in the star's core.

Today, astronomers see those elements in the puffy outer layers of Alphard -- elements dumped there by a messy neighbor.

Look for Alphard well up in the south as the sky gets good and dark. There are no other bright stars close to it -- in fact, "Alphard" is from an Arabic name that means "the solitary one." But it does form a wide triangle with two bright but distant stars: Procyon, which is well to the right of Alphard, and Regulus, a little closer to the star's upper left.

Script by Damond Benningfield, Copyright 2011


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