Brown dwarfs are substellar objects that occupy the mass range between the heaviest gas giant planets and the lightest stars.
What are brown dwarfs?
Unlike the stars in the main-sequence, they are not massive enough to sustain nuclear fusion of ordinary hydrogen to helium in their cores. They are, however, thought to fuse deuterium and to fuse lithium if their mass is above a debated threshold of 13 MJ and 65 MJ, respectively. It is also debated whether brown dwarfs would be better defined by their formation processes rather than by their supposed 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. At a distance of about 6.5 light years, the nearest known brown dwarf is Luhman 16, a binary system of brown dwarfs discovered in 2013. DENIS-P J082303.1-491201 b is listed as the most-massive known exoplanet (as of March 2014) in NASA’s exoplanet archive, despite having a mass (28.5±1.9 MJ) more than twice the 13-Jupiter-mass cutoff between planets and brown dwarfs.
The objects now called “brown dwarfs” were theorized to exist in the 1960s by Shiv S. Kumar 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. In 1975, Jill Tarter suggested the term “brown dwarf”, using brown as an approximate color.
Image: Chuck Carter & Gregg Hallinan / Caltech
Text: Wikipedia contributors. “Brown dwarf.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 26 Jul. 2017. Web. 9 Aug. 2017.