What is Brown dwarf?
[[File:Brown Dwarf Gliese 229B.jpg|thumb|250px|right|The smaller object is Gliese 229B, about 20 to 50 times the mass of Jupiter, orbiting the star [[Gliese 229]]. It is in the constellation [[Lepus (constellation)|Lepus]], about 19 light years from Earth.]] A '''brown dwarf''' is an object which is made of the same stuff as stars, but does not have enough mass for [[nuclear fusion|hydrogen fusion]] (combining [[hydrogen]] [[atoms]] into [[helium]] atoms). Hydrogen fusion is what makes [[Star|stars]] glow. Brown dwarfs are not massive enough to do this, so they are not stars. On the other hand, they are not regular giant planets, because they do glow. There are probably lots of them, but few have been found because they have only a very [[Absolute magnitude|dim glow]]. Their mass is between the heaviest [[gas giant]]s and the lightest stars, with an upper limit around 75 to 80 times the mass of [[Jupiter]] (''M<sub>J</sub>'').<ref>{{cite web|first = Alan|last = Boss|date = 2001|url = http://www.carnegieinstitution.org/News4-3,2001.html|title = Are they planets or what?|publisher = Carnegie Institution of Washington|accessdate = 2006-06-08 |archiveurl = https://web.archive.org/web/20060928065124/http://www.carnegieinstitution.org/News4-3,2001.html <!-- Bot retrieved archive --> |archivedate = 2006-09-28}}</ref> Brown dwarfs more massive than 13 ''M<sub>J</sub>'' are thought to fuse [[deuterium]] and those above ~65 ''M<sub>J</sub>'', fuse [[lithium]] as well.<ref>{{cite web|url=http://www.universetoday.com/19237/dense-exoplanet-creates-classification-calamity/|title=Dense exoplanet creates classification calamity|author=Nicholos Wethington|website=Universe Today|date=2008|accessdate=January 30, 2013}}</ref> Despite their name, most brown dwarfs would appear [[magenta]] to the human eye.<ref name=ab>{{cite web |url=http://astro.berkeley.edu/~gmarcy/astro160/papers/brown_dwarfs_failed_stars.pdf |title=Burgasser A.J. 2008. Brown dwarfs: failed stars, super Jupiters |accessdate=2013-03-16 |archive-date=2015-02-14 |