| definition |
A star-like object whose mass is too small to sustain hydrogen fusion in its interior
and become a star. Brown dwarfs are substellar objects and occupy an intermediate
regime between those of stars and giant planets. With a mass less than 0.08 times
that of the Sun (about 80 Jupiter masses), nuclear reactions in the core of brown
dwarfs are limited to the transformation of deuterium into Helium-3. The reason is
that the cores of these objects are supported against gravitational collapse by electron
degeneracy pressure (at early spectral types) and Coulomb pressure (at later spectral
types). Brown dwarfs, as ever cooling objects, will have late M dwarf spectral types
within a few Myrs of their formation and gradually evolve as L, T and Y dwarfs brown
dwarf cooling. As late-M and early-L dwarfs, they overlap in temperature with the
cool end of the stellar main sequence (M dwarf, L dwarf, T dwarf, Y dwarf). In contrast
to the OBAFGKM sequence, the M-L-T-Y sequence is an evolutionary one.
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