Brown dwarf

A substellar object more massive than a planet but too light to sustain hydrogen fusion. It forms like a star and cools over time, radiating mostly infrared light.

Deuterium burning: Nuclear fusion in which deuterium nuclei combine, releasing energy. The most massive brown dwarfs can briefly fuse deuterium, unlike ordinary planets.
Hydrogen-burning limit: The minimum mass at which an object can sustain hydrogen fusion in its core. Objects below this threshold cannot become ordinary hydrogen-burning stars.
Star formation: The formation of stars through the gravitational collapse of dense regions in molecular clouds. Many brown dwarfs appear to originate through the same cloud-collapse process.
Teide 1: A brown dwarf in the Pleiades cluster, identified in 1995 as one of the first confirmed examples. Its confirmation established that objects below the hydrogen-burning limit exist.
Brown dwarf desert: The observed scarcity of brown dwarf companions at certain close orbital distances from stars. Its cause may reveal how brown dwarfs form and migrate in stellar systems.
Hydrogen fusion: Nuclear fusion that combines hydrogen nuclei into helium and powers ordinary stars. Brown dwarfs fall below the mass needed to sustain this process.
Deuterium-burning limit: The approximate mass above which an object can fuse deuterium early in its evolution. This threshold helps distinguish massive brown dwarfs from lower-mass planetary objects.
Molecular cloud: A cold, dense interstellar cloud composed mainly of molecular hydrogen and dust. Brown dwarfs can form when small regions of such clouds collapse under gravity.
Gliese 229B: A methane-rich brown dwarf orbiting the nearby star Gliese 229. Its spectrum provided early evidence for cool, methane-bearing brown dwarf atmospheres.
Free-floating planet: A planetary-mass object that does not orbit a star. Some isolated objects resemble brown dwarfs, making their formation history difficult to classify.

Linked from 34 pages