Sub-brown dwarf

A sub-brown dwarf is an astronomical object below the usual brown-dwarf mass range, often defined as less than about 13 Jupiter masses. It may form like a star through gravitational collapse or like a planet within a disk.

Brown dwarf: A substellar object too low in mass to sustain hydrogen fusion in its core. The broader object class supplies the upper-mass comparison for sub-brown dwarfs.
Molecular cloud: A cold, dense interstellar cloud of gas and dust where stars can form. Gravitational collapse of cloud fragments can produce isolated sub-brown dwarfs.
OTS 44: A free-floating object in the Chamaeleon I star-forming region, with a mass of roughly 12 Jupiter masses. It is a prominent young example near the conventional deuterium-burning boundary.
Exoplanet: A planet orbiting a star other than the Sun, or a remnant of such a planet after ejection. Unlike a sub-brown dwarf label, exoplanet status conventionally depends on an object's formation or orbital history.
Planetary-mass object: An astronomical object with a mass comparable to that of a planet, regardless of how it formed or what it orbits. This mass-based category includes many objects called sub-brown dwarfs.
Gravitational collapse: The contraction of matter under its own gravity when internal support cannot resist its weight. This star-like formation route can create free-floating objects below the brown-dwarf range.
PSO J318.5−22: A young, free-floating planetary-mass object in the Beta Pictoris moving group. Its isolated status and planetary-scale mass make it a well-studied sub-brown-dwarf candidate.
Rogue planet: A planetary-mass object that is not gravitationally bound to a star. The term emphasizes isolation, while sub-brown dwarf emphasizes mass and possible star-like formation.
Deuterium fusion: The fusion of deuterium nuclei, which can occur temporarily in sufficiently massive young substellar objects. Its approximate ignition threshold near 13 Jupiter masses often marks the brown-dwarf boundary.
Protostellar disk: A rotating disk of gas and dust surrounding a newly forming star. A disk can form low-mass companions that later become isolated through ejection.

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