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jueves, 10 de marzo de 2011

'Very Cold' Brown Dwarf Discovered

A brown dwarf, about 75 light-years from Earth, has hit a new low. In fact, its temperature is so low that it is about the same temperature as the cup of tea sitting at my desk. Ladies and gentlemen, meet "CFBDSIR J1458+1013B," the sub-100 degree Celsius (212 F) failed star.*

A group of astronomers headed by Michael Liu, of the University of Hawaii, used the awesome power of adaptive optics on the 10-meter Keck II Telescope on Mauna Kea to probe the very faint infrared signature of this brown dwarf -- which exists as a brown dwarf binary, orbiting with its partner, CFBDSIR J1458+1013A -- revealing that the object may belong to a notoriously rare type of brown dwarf. This object is the faintest brown dwarf spotted by far and it is estimated to be only 6-15 times the mass of Jupiter.

You may have heard brown dwarfs being referred to as "failed stars" as they are not massive enough to support nuclear fusion in their cores, and yet they can't be called "planets" as they don't exhibit chemical differentiation with depth and have convective flows -- a very star-like quality. Therefore, they exist in a stellar hinterland, where they are neither a star or a planet, and yet exhibit characteristics of both.

But astronomers still classify brown dwarfs by their spectral type (a scale of letters assigned to the luminosity of stars), which relates to their temperature. At the lowest, coolest end of the scale, radiating in infrared wavelengths, are the oddball brown dwarfs.

So far, the coolest brown dwarfs observed exist at the lowest end of the scale, with a spectral class of "T." However, there is a theoretical class "Y" that is even cooler than the T-class brown dwarfs -- they are predicted to have a temperature less than 225 degrees Celsius (440 F).

More Like a Planet? More Like a Star?

Although Y-class candidates have been spotted by other instruments, the Keck telescope has put a very tight constraint on the temperature of CFBDSIR J1458+1013B and it looks as if this brown dwarf has more "planet-like" qualities than "star-like" qualities, with a temperature of 97 degrees Celsius (give or take 40 degrees C).

Could CFBDSIR J1458+1013B be the missing link between stars and planets? How can we work out if this object is more like Jupiter, say, or more like the sun?

Usually, water will exist in a gaseous state in brown dwarf atmospheres. But at such low temperatures, it is expected that water in the brown dwarf's atmosphere will condense to form clouds. Although it is hard to detect condensing water in this brown dwarf's atmosphere, it is certainly a prime "Y" class candidate.

Regardless, CFBDSIR J1458+1013B is the coolest brown dwarf in the cosmic neighborhood and it could help us understand the point at which a star becomes a star and a planet becomes a planet.

*Although brown dwarfs are known as "failed stars," I like to refer to them as "overachieving planets." Whoever said that becoming a star was the pinnacle of stellar living anyway?

Image credit: NASA, ESA and G. Bacon (STScI)

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