A sub-brown dwarf is an astronomical object of planetary mass that is not orbiting a star and is not considered to be a brown dwarf because its mass is below the limiting mass for thermonuclear fusion of deuterium (about 13 Jupiter masses).[1]
Contents |
Sub-brown dwarfs are formed in the manner of stars, through the collapse of a gas cloud (perhaps with the help of photo-erosion), and not through accretion or core collapse from a circumstellar disc. This formation distinction between a sub-brown dwarf and a planet is not universally agreed upon; astronomers are divided into two camps as whether to consider the formation process of a planet as part of its division in classification.[2] One reason for the dissent is that oftentimes it may not be possible to determine the formation process: for example an accretion-formed planet around a star may get ejected from the system to become free-floating, and likewise a cloud-collapse-formed sub-brown dwarf formed on its own in a star cluster may get captured into orbit around a star.
The smallest mass of gas cloud that could collapse to form a sub-brown dwarf is about 1 MJ.[3] This is because to collapse by gravitational contraction requires radiating away energy as heat and this is limited by the opacity of the gas.[4] A 3 MJ candidate is described in the paper Dusty Disks at Bottom of IMF.
|
||||||||||||||||||||||||||||||||||||||||||||