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Newfound neighbor to solar system is a cool slacker

Nearby brown dwarf never became a star

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3:33pm, April 9, 2010
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The solar system is surrounded by a bunch of abject failures, a new discovery suggests. Astronomers have found the nearest known brown dwarf, or failed star, residing about 9 light-years from Earth.

That places this brown dwarf among the 10 closest stellar or substellar systems to the solar system, researchers report in an article posted online April 5 (http://arxiv.org/abs/1004.0317). Its temperature, about baking temp in a home oven, makes it the coolest brown dwarf known.

“Everyone is going to want to jump on this finding,” comments brown dwarf observer J. Davy Kirkpatrick of Caltech, who was not part of the discovery team. “I wouldn’t be surprised if someone started looking at it” the night the paper came out, he adds.   

Astronomers calculate, based on the percentage of stars that fail to develop in young star clusters, that brown dwarfs should be at least as common in the Milky Way as stars. The new finding, combined with recent discoveries of other nearby brown dwarfs, suggests that the solar neighborhood is rife with these dim, hard-to-detect bodies. Indeed, the nearest body to the solar system may be a brown dwarf rather than a bona fide star, comments theorist Gibor Basri of the University of California, Berkeley.

Philip Lucas of the University of Hertfordshire in England and his colleagues discovered the dim body, dubbed UGPSJ0722-05, in a sky survey conducted with the United Kingdom Infrared Telescope atop Hawaii’s Mauna Kea. Follow-up spectra recorded by the Gemini North Telescope, also on Mauna Kea, revealed that water vapor and methane in the object absorbed light more strongly than the coolest known brown dwarfs, an indication that the newfound body is even cooler. The team estimates its temperature is 125Ë to 225Ë Celsius.

“I think this is quite an important finding,” says Basri. “There has long been speculation that a brown dwarf could be found even closer [than the nearest known star, Proxima Centauri, 4.2 light-years away]; this is another step towards that.” If such a nearby object exists, it would have to be exceptionally faint and cool, he adds.

Like all brown dwarfs, the object is a ball of gas that weighs between five and 30 times Jupiter’s mass, which is not enough to sustain the nuclear burning at its core that stars undergo. Yet brown dwarfs are thought to form in the same way that stars are born, from the gravitational collapse of a molecular cloud of gas.

Lucas declined to comment on the study because he and his colleagues have submitted their paper to Nature.  

In their online paper, Lucas and his colleagues suggest that the newly discovered brown dwarf is so cool that it might be the first member of a new class of ultralow temperature dwarfs. Although one fingerprint of such a new class, absorption of infrared light by ammonia, appears to be missing, only “time will tell” if the discovery merits a new classification, the researchers note. NASA’s recently launched WISE spacecraft (Heat-seeking WISE spacecraft to scan the skies), an infrared satellite deigned to hunt brown dwarfs and other cool objects, is likely to find the very closest brown dwarfs to Earth, says Kirkpatrick.

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