The Substellar Family
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Brown dwarfs are objects intermediate in mass between planets and stars, too large to have formed as planets, too small to sustain hydrogen fusion. Although they have been called “a poor excuse for a star,” they are embraced by stellar astronomers and have even found a place in the standard stellar classification system. They range in mass from 13 to 80 times the mass of Jupiter, about 8% of a solar mass, but most are about the size of Jupiter. They are completely boiling, convective objects. Brown dwarfs are difficult to detect due to their very low luminosity, which during the first hundred million years or so derives from gravitational contraction, after which they become even fainter. Their temperature of 1,000 K and less dictates that they radiate primarily in the infrared region of the spectrum and are especially amenable to detection by infrared telescopes. Brown dwarfs can undergo deuterium and lithium fusion during their first ten million years.