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 3He. 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.
These objects were first postulated by Kumar (1963, ApJ 137, 1121
& 1126) and Hayashi & Nakano (1963, Prog. Theor.Phys. 30, 460).
See also: The term brown dwarf was first used by Jill Tarter in her 1975 PhD thesis;
→ brown; → dwarf.
