Brown dwarf
From Conservapedia
A Brown Dwarf is a sub-stellar object that has an intermediate mass between a star and a large gas giant planet. Sometimes described as "failed stars", they lack the necessary mass to start or maintain hydrogen burning nuclear fusion reactions in their cores.
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History
The name "Brown Dwarf" was first coined by Jill Tarter in 1975 for a classification of sub-stellar objects in space which are unable to sustain hydrogen fusion.
The first located Brown Dwarf was discovered in 1988 as a companion to the star GD 165, which was too cool to be classified as an M class star. For almost a decade, GD 165B, today known as a L class brown dwarf was the only known object that could be classified as such. In 1995 this changed, using a combination of mass determination, spectroscopic studies, and direct imaging another confirmed brown dwarf was discovered as a companion to Gliese 229. The discovery would later help establish a new class of brown dwarfs known as "T dwarfs". Today hundreds of brown dwarfs are known[1].
Classification
There are three classifications of brown dwarfs today:
Spectral class L
L dwarfs are defined in the red opitcal region, much like M class stars, but have spectra defined by strong metal hydride bands (FeH, CrH, MgH, CaH) and alkali lines (Na I, K I, Cs I, Rb I)[1]. The surface temperature of of L class dwarfs typical average around 1,500K to 2,200K. Teide 1 is an example of a L dwarf.
Spectral class T
Cooler then the L class dwarfs, T class, or methane dwarfs are have a surface range of 1,500K to a mere 800K. Their spectra display strong absorption by methane (CH4), and water (H2O)[1]. If seen visually, they would appear as dark magenta. Gliese 229b is an example of a T dwarf[2].
Spectral class Y
Y dwarfs are believed to be even cooler than T dwarfs, and are considered theoretical[3]. Such dwarfs would have surface temperatures under 700K. In March 2008, a brown dwarf called CFBDS J005910.90-011401.3 was discovered, which a surface temperature of only 620K, and is believed to be the first such Y dwarf found[4].
Detecting brown dwarfs
Because of the very limited amount of light brown dwarfs give, methods other then observations in the visual spectrum are used to discover them. One method of detection is through the large amount of infrared radiation such objects emit, allowing observations using infrared equipment. They are also detected via the wobble that a brown dwarf would cause in the motion of a parent or companion star. Thus radial velocity is used to find a large amount of brown dwarfs. A telescope equipped with a coronagraph may also be used to detect brown dwarfs.
