Not-Brown Dwarfs

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The language of astronomy is filled with terms that aren’t quite right. The word “planet,” for example, means “wanderer,” yet the planets don’t wander at all -- they follow well-defined paths around the Sun. And “asteroid” means “starlike,” even though an asteroid isn’t like a star -- it’s a chunk of rock and ice.

A more recent example is “brown dwarf” -- an object that’s more massive than a planet, but not massive enough to shine as a star.

The “dwarf” part of the name is correct -- brown dwarfs are smaller than true stars, and they’re even smaller than some planets.

But brown dwarfs aren’t brown. They glow because they’re hot, and there’s no way for a glowing ball of hot gas to produce brown light.

Figuring out a brown dwarf’s true color is tricky, though. In part, that’s because brown dwarfs have a wide range of surface temperatures -- from a few hundred degrees to a few thousand. But it’s also because brown dwarfs have complex atmospheres that contain a variety of compounds that aren’t found in true stars. Some may even have bands of clouds, like the planet Jupiter.

A couple of studies have taken a crack at calculating the color of brown dwarfs. One study said they should look orangey-red. Another found that a single known brown dwarf shines bright red, but many of them should trend toward purple. That would make them sound like characters from the Land of Oz: purple dwarfs.

More about these colorful objects tomorrow.

Script by Damond Benningfield, Copyright 2010

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