Sub-brown dwarf


A sub-brown dwarf or planetary-mass brown dwarf is an astronomical object that formed in the same manner as stars and brown dwarfs but that has a mass below the limiting mass for thermonuclear fusion of deuterium.
Some researchers call them free-floating planets whereas others call them planetary-mass brown dwarfs.

Description

Sub-brown dwarfs are formed in the manner of stars, through the collapse of a gas cloud but there is no consensus amongst astronomers on whether the formation process should be taken into account when classifying an object as a planet. Free-floating sub-brown dwarfs can be observationally indistinguishable from rogue planets, which originally formed around a star and were ejected from orbit. Similarly, a sub-brown dwarf formed free-floating in a star cluster may be captured into orbit around a star, making distinguishing sub-brown dwarfs and large planets also difficult. A definition for the term "sub-brown dwarf" was put forward by the IAU Working Group on Extra-Solar Planets, which defined it as a free-floating body found in young star clusters below the lower mass cut-off of brown dwarfs.

Lower mass limit

The smallest mass of gas cloud that could collapse to form a sub-brown dwarf is about 1 Jupiter mass. This is because to collapse by gravitational contraction requires radiating away energy as heat and this is limited by the opacity of the gas. A 3 MJ candidate is described in a 2007 paper.

List of possible sub-brown dwarfs

Orbiting one or more stars

There is no consensus whether these companions of stars should be considered sub-brown dwarfs or planets.
There is no consensus whether these companions of brown dwarfs should be considered sub-brown dwarfs or planets.
Also called Rogue planets: