Early theorizing 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 dwarfs, a classification for dark substellar objects floating freely in space that were not massive enough to sustain hydrogen fusion. However, (a) the term black dwarf was already in use to refer to a cold white dwarf; (b) red dwarfs fuse hydrogen; and (c) these objects may be luminous at visible wavelengths early in their lives. Because of this, alternative names for these objects were proposed, including and substar. In 1975, Jill Tarter suggested the term "brown dwarf", using "brown" as an approximate color.
Early theorizing 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 dwarfs, a classification for dark substellar objects floating freely in space that were not massive enough to sustain hydrogen fusion. However, (a) the term black dwarf was already in use to refer to a cold white dwarf; (b) red dwarfs fuse hydrogen; and (c) these objects may be luminous at visible wavelengths early in their lives. Because of this, alternative names for these objects were proposed, including and substar. In 1975, Jill Tarter suggested the term "brown dwarf", using "brown" as an approximate color.