Editing Brown dwarf (section)

==== Spectral class T ====
{{main|T dwarf}}
[[Image:T-dwarf-nasa-hurt.png|thumb|left|Artist's concept of a T dwarf]]

As GD 165B is the prototype of the L dwarfs, [[Gliese 229]]B is the prototype of a second new spectral class, the '''T dwarfs'''. T&nbsp;dwarfs are pinkish-magenta. Whereas [[near-infrared]] (NIR) spectra of L dwarfs show strong absorption bands of H<sub>2</sub>O and [[carbon monoxide]] (CO), the NIR spectrum of Gliese 229B is dominated by absorption bands from [[methane]] (CH<sub>4</sub>), a feature which in the Solar System is found only in the giant planets and [[Titan (moon)|Titan]]. CH<sub>4</sub>, H<sub>2</sub>O, and molecular [[hydrogen]] (H<sub>2</sub>) 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 [[sodium|Na]] and [[potassium|K]]. These differences led [[J. Davy Kirkpatrick]] to propose the T spectral class for objects exhibiting H- and K-band CH<sub>4</sub> absorption. {{As of|2013}}, 355 T&nbsp;dwarfs were known.<ref name="DwarfArchives"/> 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]].<ref name=burrows>{{cite journal |last1=Burrows |first1=Adam |last2=Hubbard |first2=William B. |last3=Lunine |first3=Jonathan I. |last4=Liebert |first4=James |year=2001 |title=The theory of brown dwarfs and extrasolar giant planets |journal=[[Reviews of Modern Physics]] |volume=73 |issue=3 |pages=719–765 |doi=10.1103/RevModPhys.73.719 |bibcode=2001RvMP...73..719B |arxiv=astro-ph/0103383 |s2cid=204927572 }}</ref><ref>[http://spider.ipac.caltech.edu/staff/davy/2mass/science/comparison.html "An Artist's View of Brown Dwarf Types"] {{Webarchive |first=Robert |last=Hurt |newspaper=Infrared Processing and Analysis Center |url=https://web.archive.org/web/20111117180311/http://spider.ipac.caltech.edu/staff/davy/2mass/science/comparison.html |date=2011-11-17 }}</ref> Early observations limited how distant T-dwarfs could be observed. T-class brown dwarfs, such as [[WISE 0316+4307]], have been detected more than 100 light-years from the Sun. Observations with JWST have detected T-dwarfs such as [[UNCOVER-BD-1]] up to 4500 parsec distant from the sun.