Wednesday, April 16, 2008

Stargeek Atlantis, Episode Four

It's so cool it's hot. Except it's not hot, which is why it's cool. Well, it is hot but it's not hot by what's actually hot, so it's actually cool, which is what makes it cool. Or so told us a few days ago.
An international team of astronomers has discovered the coldest brown dwarf star ever observed. This finding is a new step toward filling the gap between stars and planets. ...

The brown dwarf is named CFBDS J005910.83-011401.3 (it will be called CFBDS0059 in the following). Its temperature is about 350 degrees C and its mass about 15-30 times the mass of Jupiter, the largest planet of our solar system. Located about 40 light-years from our solar system, it is an isolated object, meaning that it doesn't orbit another star.
To give you an idea of how small and cool that is for a star, the Sun is well over 30 times as massive and its surface temperature is more than 17 times hotter. Indeed, the dwarf's surface temperature is only moderately above the ignition temperature of a safety match and is about one-fifth of that of a blast furnace.
Brown dwarfs are intermediate bodies between stars and giant planets (like Jupiter). The mass of brown dwarfs is usually less than 70 Jupiter masses. Because of their low mass, their central temperature is not high enough to maintain thermonuclear fusion reactions over a long time. In contrast to a star like our Sun, which spends most of its lifetime burning hydrogen hence keeping a constant internal temperature, a brown dwarf spends its lifetime getting colder and colder after having been formed. ...

To date, two classes of brown dwarfs have been known: the L dwarfs (temperature of 1200-2000 degrees C), which have clouds of dust and aerosols in their high atmosphere, and the T dwarfs (temperature lower than 1200 degrees C), which have a very different spectrum because of methane forming in their atmosphere. Because it contains ammonia and has a much lower temperature than do L and T dwarfs, CFBDS0059 might be the protoype of a new class of brown dwarfs to be called the Y dwarfs. This new class would become the coldest stellar objects, hence the missing link toward giant planets. Astronomers could then fill in the domain from the hottest stars to the giant planets of less than -100 degrees C.
"There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy." There is a whole lotta crap out there still to be discovered. I just said it but I'll say it again: That's what makes science so cool.

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