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Brown
Brown dwarfs are substellar objects too low in mass to sustain hydrogen-1 fusion reactions in their cores, unlike main-sequence stars, which can. They occupy the mass range between the heaviest gas giants and the lightest stars, with an upper limit around 75[1] to 80 Jupiter masses(MJ). Brown dwarfs heavier than about 13 MJ are thought to fuse deuterium and those above ~65 MJfuse lithium as well.[2]

The difference between a very-low-mass brown dwarf and a giant planet (~13 Jupiter masses) has been recently debated.[3] One school of thought is based on formation; another, interior physics.[3]

Dwarfs are categorized by spectral classification, with the major types being M, L, T, and Y.[3] Despite their name, brown dwarfs are different colours.[3] Many brown dwarfs would likely appear magenta to the human eye according to A. J. Burgasser,[3] whereas another source has noted orange/red.[4] The term brown dwarf was not chosen to indicate their colour.[3]

Another debate is whether brown dwarfs should have experienced fusion at some point in their history. Some planets are known to orbit brown dwarfs: 2M1207bMOA-2007-BLG-192Lb, and 2MASS J044144b. Brown dwarfs may have fully convective surfaces and interiors, with no chemical differentiation by depth.[5]

At a distance of about 6.5 light years, the nearest known brown dwarf is Luhman 16Luhman 16, a binary system of brown dwarfs discovered in 2013.

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