The brown-dwarf desert is a theorized range of orbits around a star on which brown dwarfs cannot exist as a companion object.[1] This is usually up to 5 AU around solar mass stars. The paucity of brown dwarfs in close orbits was first noted between 1998–2000 when a sufficient number of extrasolar planets had been found to perform statistical studies. Astronomers discovered there is a distinct shortage of brown dwarfs within 5 AU of the stars with companions, while there was an abundance of free-floating brown dwarfs being discovered.[2] Subsequent studies have shown that brown dwarfs orbiting within 3–5 AU are found around less than 1% of star with a mass similar to the Sun.[3]
This desert occurs because if a brown dwarf were to form, it would have to do so at the same time as its companion star. If the brown dwarf formed within 5 AU of its companion star, it would begin migration towards the star and eventually become consumed by the larger star.
It has recently been observed that very-low-mass binaries could destroy the theory of brown-dwarf deserts. This is because low-mass binaries are seen to orbit within 5AU; however, due to the low mass of the larger companion, this matter is still a topic of debate.