Brown dwarfs

Brown dwarfs are sub-stellar objects with a mass 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 (). 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 ), and whether brown dwarfs are required to have experienced fusion at some point in their history. In any event, brown dwarfs heavier than 13 do fuse deuterium and those above ~65 also fuse lithium. The only planet known to orbit a brown dwarf is 2M1207b.
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[Picture] Celestial objects, formed via gravitational collapse, which are less than 0.08 solar masses . Below this mass limit, the temperature and pressure in the central regions of the body are insufficient to ignite the nuclear fusion of hydrogen into helium at its core. Brown dwarfs do radiate energy into space but it is in the infra red region of the electromagnetic spectrum. The radiation carries away the residual energy left over from the formation of the brown dwarf. In appearance and composition, brown dwarfs may be very similar to Jupiter. They are theorised to exist in vast numbers throughout the galaxy and yet, because of their small size and meagre energy output, they are very difficult to detect. Nevertheless, searches for brown dwarfs are carried out all the time and several candidate objects have been reported.