A sub-brown dwarf or planetary-mass brown dwarf is an

astronomical object An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''body'' are often u ...

that formed in the same manner as

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

s and

brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...

s (i.e. through the collapse of a gas cloud) but that has a

planetary mass In astronomy, planetary mass is a measure of the mass of a planet-like astronomical object. Within the Solar System, planets are usually measured in the astronomical system of units, where the unit of mass is the solar mass (), the mass of the Su ...

, therefore by definition below the limiting mass for

thermonuclear fusion Thermonuclear fusion is the process of atomic nuclei combining or “fusing” using high temperatures to drive them close enough together for this to become possible. There are two forms of thermonuclear fusion: ''uncontrolled'', in which the re ...

deuterium Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two stable isotopes of hydrogen (the other being protium, or hydrogen-1). The nucleus of a deuterium atom, called a deuteron, contains one proton and one ...

(about ). Some researchers call them free-floating planets whereas others call them planetary-mass brown dwarfs. They are sometimes categorized as Y spectral class brown dwarfs.

Description

Sub-brown dwarfs are formed in the manner of

s, through the collapse of a gas cloud (perhaps with the help of photo-erosion) 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 (WGESP), 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 (M_J). This is because to collapse by

gravitational In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the str ...

contraction requires radiating away energy as heat and this is limited by the opacity of the gas. A 3 M_J 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. *

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B * DT Virginis c * FW Tauri b *

HD 106906 b HD 106906 b is a directly imaged planetary-mass companion and candidate exoplanet orbiting the star , in the constellation Crux at about from Earth. It is estimated to be about eleven times the mass of Jupiter and is located about 738 ...

ROXs 42Bb ROXs 42Bb is a directly imaged planetary-mass companion to the binary M star ROXs 42B, a likely member of the Rho Ophiuchi cloud complex. The companion was announced/discovered on October 17, 2013 by University of Toronto astronomer Thayne Cur ...

Orbiting a brown dwarf

There is no consensus whether these companions of brown dwarfs should be considered sub-brown dwarfs or planets. * The 5–10M_J companion of

2MASS J04414489+2301513 2MASS J04414489+2301513 (often abbreviated as 2M J044144) is a young star system hosting a planet and a couple of brown dwarfs, approximately 470 light years (145 parsecs) away. The 2MASS J04414489+2301513 primary (a brown dwarf) has a la ...

2M1207b 2M1207b is a planetary-mass object orbiting the brown dwarf 2M1207, in the constellation Centaurus, approximately 170 light-years from Earth.

Free-floating

Also called rogue planets: *

WISE 0855–0714 WISE may refer to: Arts, entertainment, and media *WISE (AM), a radio station licensed to Asheville, North Carolina * WISE-FM, a radio station licensed to Wise, Virginia *WISE-TV, a television station licensed to Fort Wayne, Indiana Education *We ...

3–10 M_J about 7 light years away *

S Ori 52 S, or s, is the nineteenth letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''ess'' (pronounced ), plural ''esses''. Histor ...

* UGPS 0722-05 10–25 M_J 13 light years away * Cha 110913-773444 5–15 M_J 163 light years away *

CFBDSIR 2149−0403 CFBDSIR 2149-0403 (full designation CFBDSIR J214947.2-040308.9) is a free-floating planetary-mass object or possibly a high-metallicity, low-mass brown dwarf in the constellation Aquarius. Originally, it was thought to be part of the AB Doradus ...

4–7 M_J 130 light years away *

OTS 44 OTS 44 is a free-floating planetary-mass object or brown dwarf located at in the constellation Chamaeleon near the reflection nebula IC 2631. It is among the lowest-mass free-floating substellar objects, with approximately 11.5 times ...

11.5 M_J 550 light years away

References

{{DEFAULTSORT:Sub-Brown Dwarf + Types of planet Planemos Free-floating substellar objects