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Not-Brown Dwarfs

November 23, 2010

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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