In astronomy, a brown dwarf is a celestial body with a
starlike composition but a
mass between that of a giant
planet and the smallest possible stars. Too small to initiate the nuclear reactions by which stars shine, it glows feebly in the
infrared. The largest solar-system planet, Jupiter, has a starlike composition and radiates some energy, but it is probably about 50 times smaller than the smallest brown
dwarfs.
Astronomers use advanced infrared imaging techniques to search for brown dwarfs, and in 1994, Palomar astronomers photographed one orbiting a small star, Gliese 229B, 19 light-years away in the constellation Lepus. Several others have since been detected. Brown dwarfs might help to account for the supposed "missing mass" of the universe (see mass, missing) that cosmology theories incorporate as an unexplained problem.
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