Brown dwarf

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Brown dwarfs are sub-stellar objects which are too low in mass to sustain stable hydrogen fusion. Their mass is below that necessary to maintain hydrogen-burning nuclear fusion reactions in their cores, as do stars on the main sequence, but which have fully convective surfaces and interiors, with no chemical differentiation by depth. Brown dwarfs occupy the mass range between that of large gas giant planets and the lowest mass stars; this upper limit is between 75 and 80 Jupiter masses (MJ). Currently there is some debate as to what criterion to use to define the separation between a brown dwarf from a giant planet at very low brown dwarf masses (~13 MJ ), and whether brown dwarfs are required to have experienced fusion at some point in their history. In any event, brown dwarfs heavier than 13 MJ do fuse deuterium and those above ~65 MJ also fuse lithium. Some planets are known to orbit brown dwarfs: 2M1207b, MOA-2007-BLG-192Lb, and 2MASS J044144‎.

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