Sunday, January 13, 2013

Weather on a Star




Astronomers using both the Hubble and the Spitzer space telescopes have gotten an indication of weather in the atmosphere of a kind of "failed star" called a brown dwarf. Stars are so far away that, in general, they look like points of light, even in our biggest telescopes -- so this is quite an achievement.

Brown dwarfs (a name coined by Jill Tarter, the scientist on whom Jodie Foster's character in the movie "Contact" was based) are large balls of hot gas that "ain't got what it takes" to be a star. They don't have the mass to continue making energy on their own, so after a brief period of glowing from how compressed they get at birth, they just fade away. (I like to compare them to all the actors that come to Hollywood with high hopes, maybe get a role as an extra in a TV show, but never make it to be real stars.)

This particular brown dwarf (which doesn't have a name, only a long catalog number) was observed not in visible light but in "infra-red" or heat rays, which allow us to see cooler glows. Both the Hubble and the Spitzer can detect and measure infra-red waves, but they "see" them from different depths in the atmosphere of the star. Daniel Apai, one of the astronomers doing the work, compared this to medical imaging, where different kinds of instruments can see different layers of your body.

As shown in the accompanying artist's interpretation (NOT a photograph!), there appear to be huge and deep clouds in the star's atmosphere, some of them as large as planet Earth! They move around in the atmosphere as the star spins every 90 minutes or so. They may somewhat resemble the largest regularly scheduled cloud we know in the solar system, the Great Red Spot of Jupiter (see the beautiful image below, from the Galileo spacecraft which orbited Jupiter.)

But the temperature in a brown dwarf is not cool like the atmosphere of Jupiter, so the clouds are likely to be made of different stuff from clouds on Earth and Jupiter. What might condense into clouds in a region which is 1100-1300 degrees Fahrenheit (600-700 degrees Celsius) in temperature? Mark Marley, another scientist on the team, suggests they are "composed of hot grains of sand, liquid drops of iron, and other exotic compounds."

Isn't it amazing that we can now do weather reports from a star?




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