Editing Brown dwarf (section)

=== Early theorizing ===
[[File:PIA23685-Planets-BrownDwarfs-Stars.jpg|thumb|left|200px|Planets, brown dwarfs, stars (not to scale)]]
The objects now called "brown dwarfs" were theorized by Shiv S. Kumar in the 1960s to exist and were originally called [[black dwarf]]s,<ref>{{cite journal |last=Kumar |first=Shiv S. |title=Study of Degeneracy in Very Light Stars |journal=Astronomical Journal |volume=67 |page=579 |date=1962 |doi=10.1086/108658 |bibcode=1962AJ.....67S.579K|doi-access=free }}</ref> a classification for dark substellar objects floating freely in space that were not massive enough to sustain hydrogen fusion. However, (a)&nbsp;the term black dwarf was already in use to refer to a cold [[white dwarf]]; (b)&nbsp;[[red dwarf]]s fuse hydrogen; and (c)&nbsp;these objects may be luminous at visible wavelengths early in their lives. Because of this, alternative names for these objects were proposed, including {{not a typo|planetar}} and [[Substellar object|substar]]. In 1975, [[Jill Tarter]] suggested the term "brown dwarf", using "brown" as an approximate color.<ref name="Cain"/><ref name="JillTarter2014">{{citation |last=Tarter |first=Jill |author-link=Jill Tarter |chapter=Brown is Not a Color: Introduction of the Term 'Brown Dwarf' |pages=19–24 |editor-last=Joergens |editor-first=Viki |title=50 Years of Brown Dwarfs – From Prediction to Discovery to Forefront of Research |series=Astrophysics and Space Science Library |volume=401 |publisher=Springer |publication-date=2014 |isbn=978-3-319-01162-2 |chapter-url=https://www.springer.com/astronomy/book/978-3-319-01161-5|doi=10.1007/978-3-319-01162-2_3 |year=2014 }}</ref><ref>{{cite book |last1=Croswell |first1=Ken |title=Planet Quest: The Epic Discovery of Alien Solar Systems |date=1999 |publisher=Oxford University Press |isbn=978-0-192-88083-3 |pages=118–119 }}</ref>

The term "black dwarf" still refers to a [[white dwarf]] that has cooled to the point that it no longer emits significant amounts of light. However, the time required for even the lowest-mass white dwarf [[White dwarf#Radiation and cooling|to cool to this temperature]] is calculated to be longer than the current age of the universe; hence such objects are expected to not yet exist.<ref>{{cite web |date=April 10, 2020 |title=When will the Sun become a black dwarf? |url=https://astronomy.com/magazine/ask-astro/2020/04/when-will-the-sun-become-a-black-dwarf |access-date=2022-05-02 |website=Astronomy.com }}</ref>

Early theories concerning the nature of the lowest-mass stars and the [[hydrogen-burning limit]] suggested that a [[population I]] object with a mass less than 0.07&nbsp;[[solar mass]]es ({{Solar mass|link=y}}) or a [[population II]] object less than {{Solar mass|0.09}} would never go through normal [[stellar evolution]] and would become a completely [[degenerate star]].<ref name="Kumar1963">{{cite journal |last=Kumar |first=Shiv S. |date=1963 |title=The Structure of Stars of Very Low Mass |journal=Astrophysical Journal |volume=137 |page=1121 |bibcode=1963ApJ...137.1121K |doi=10.1086/147589 }}</ref> The resulting brown dwarf star is sometimes called a '''failed star'''.<ref>{{cite journal |last=Burgasser |first=Adam J. |date=2008-06-01 |title=Brown dwarfs: Failed stars, super jupiters |url=https://pubs.aip.org/physicstoday/article-abstract/61/6/70/931935/Brown-dwarfs-Failed-stars-super-jupitersThe?redirectedFrom=fulltext |journal=Physics Today |volume=61 |issue=6 |pages=70–71 |doi=10.1063/1.2947658 |bibcode=2008PhT....61f..70B |issn=0031-9228}}</ref> The first self-consistent calculation of the hydrogen-burning minimum mass confirmed a value between 0.07 and 0.08&nbsp;solar masses for population I objects.<ref name="Hayashi1963">{{cite journal |last1=Hayashi |first1=Chushiro |author-link1=Chushiro Hayashi |last2=Nakano |first2=Takenori |date=1963 |title=Evolution of Stars of Small Masses in the Pre-Main-Sequence Stages |journal=Progress of Theoretical Physics |volume=30 |pages=460–474 |bibcode=1963PThPh..30..460H |doi=10.1143/PTP.30.460 |number=4 |doi-access=free }}</ref><ref name=Nakano2014>{{citation |last=Nakano |first=Takenori |chapter=Pre-main Sequence Evolution and the Hydrogen-Burning Minimum Mass |pages=5–17 |editor-last=Joergens |editor-first=Viki |title=50 Years of Brown Dwarfs – From Prediction to Discovery to Forefront of Research |series=Astrophysics and Space Science Library |volume=401 |publisher=Springer |publication-date=2014 |isbn=978-3-319-01162-2 |chapter-url=https://www.springer.com/astronomy/book/978-3-319-01161-5|doi=10.1007/978-3-319-01162-2_2 |year=2014 |s2cid=73521636 }}</ref>