18:11 09 April 2010 by Ken Croswell
A dim object less than 10 light years from Earth appears to be the closest brown dwarf yet found. The "star" is so cold that any residents on an orbiting planet would see a dark sun in their starry "daytime" sky.
The discovery suggests that brown dwarfs are common and that the objects could exist even closer to Earth.
Brown dwarfs have so little mass that they never get hot enough to sustain the nuclear fusion reactions that power stars like the sun. Still, they do shine, because they glow from the heat of their formation, then cool and fade.
Philip Lucas of the University of Hertfordshire in Hatfield, UK, and his colleagues discovered the brown dwarf, named UGPS 0722-05, from the infrared radiation it gives off. It is only about 9.6 light years from Earth, a bit more than twice as far as Proxima Centauri, our nearest star after the sun.
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http://www.newscientist.com/article/dn18757-dark-sun-is-one-of-our-nearest-neighbours.html