page_title: Brown dwarf
section_title: Spectral class T
hierarchical_section_title: Brown dwarf / Observations / Classification of brown dwarfs / Spectral class T
caption_attribution_description: Snapshot and fix of an artists impression of a late M-star, L-star and a T-star.
context_page_description: A brown dwarf is a type of substellar object that has a mass between those of the heaviest gas giant planets and the least massive stars, i.e. about 13 to 75–80 times that of Jupiter, or about 2.5×10²⁸ kg to 1.5×10²⁹ kg. Below this range are the sub-brown dwarfs, and above it are the red dwarfs. Brown dwarfs may be fully convective, with no layers or chemical differentiation by depth.
  Unlike the stars in the main sequence, brown dwarfs are not massive enough to sustain nuclear fusion of ordinary hydrogen to helium in their cores. They are, however, thought to fuse deuterium. If their mass is > 65 MJ they may also fuse lithium. It is also debated whether brown dwarfs would be better defined by their formation processes rather than by their nuclear fusion reactions.
  Stars are categorized by spectral class, with brown dwarfs designated as types M, L, T, and Y. Despite their name, brown dwarfs are of different colors. Many brown dwarfs would likely appear magenta to the human eye, or possibly orange/red. Brown dwarfs are not very luminous at visible wavelengths.
  There are planets known to orbit brown dwarfs, such as 2M1207b, MOA-2007-BLG-192Lb, and 2MASS J044144b.
context_section_description: As GD 165B is the prototype of the L dwarfs, Gliese 229B is the prototype of a second new spectral class, the T dwarfs. Whereas near-infrared (NIR) spectra of L dwarfs show strong absorption bands of H₂O and carbon monoxide (CO), the NIR spectrum of Gliese 229B is dominated by absorption bands from methane (CH₄), features that were only found in the giant planets of the Solar System and Titan. CH₄, H₂O, and molecular hydrogen (H₂) collision-induced absorption (CIA) give Gliese 229B blue near-infrared colors. Its steeply sloped red optical spectrum also lacks the FeH and CrH bands that characterize L dwarfs and instead is influenced by exceptionally broad absorption features from the alkali metals Na and K. These differences led Kirkpatrick to propose the T spectral class for objects exhibiting H- and K-band CH₄ absorption. As of 2013, 355 T dwarfs are known. NIR classification schemes for T dwarfs have recently been developed by Adam Burgasser and Tom Geballe. Theory suggests that L dwarfs are a mixture of very-low-mass stars and sub-stellar objects (brown dwarfs), whereas the T dwarf class is composed entirely of brown dwarfs. Because of the absorption of sodium and potassium in the green part of the spectrum of T dwarfs, the actual appearance of T dwarfs to human visual perception is estimated to be not brown, but magenta. T-class brown dwarfs, such as WISE 0316+4307, have been detected over 100 light-years from the Sun.
caption: Artist's vision of a T-dwarf
exif: {}