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 us ...

that formed in the same manner as

star A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make ...

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 (hydrogen-1, 1H) into helium in their cores, unlike a main sequence, main-sequence star. Instead, they have ...

s (i.e. through the collapse of a gas cloud) but that has a planetary mass, 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 isotope ratio, stable isotopes of hydrogen (the other being Hydrogen atom, protium, or hydrogen-1). The atomic nucleus, nucleus of a deuterium ato ...

(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 Photo-erosion is the dispersion of the outer layers of a prestellar core by the ionizing radiation of a nearby star. This erosion prevents the accretion of these outer layers around the protostar at the centre of the core; and this, in turn, prev ...

) 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 planet A rogue planet (also termed a free-floating planet (FFP), interstellar, nomad, orphan, starless, unbound or wandering planet) is an interstellar object of planetary-mass, therefore smaller than fusors (stars and brown dwarfs) and without a ...

s, 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 The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach ...

(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 Jupiter mass, also called Jovian mass, is the unit of mass equal to the total mass of the planet Jupiter. This value may refer to the mass of the planet alone, or the mass of the entire Jovian system to include the moons of Jupiter. Jupiter is b ...

(M_J). 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 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. * WD 0806-661 B *

DT Virginis c DT Virginis, also known as Ross 458, is a binary star system in the constellation of Virgo. It has an apparent visual magnitude of 9.79 and is located at a distance of 37.6 light-years from the Sun. Both of the stars are low-mass re ...

* 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 AU ...

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 Cu ...

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 *

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

s: *

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 *Web ...

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''. History ...

* 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 Doradu ...

4–7 M_J 130 light years away * OTS 44 11.5 M_J 550 light years away

References

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