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 (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 dwarfs (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 of
deuterium (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
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, 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 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
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 (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
*
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
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:
*
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Education
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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
See also
*
Brown dwarf
*
Fusor (astronomy)
*
Giant planet
*
Hot Jupiter
*
Red dwarf
''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. T ...
*
Rogue planet
*
Substellar object
A substellar object, sometimes called a substar, is an astronomical object the mass of which is smaller than the smallest mass at which hydrogen fusion can be sustained (approximately 0.08 solar masses). This definition includes brown dwarfs and fo ...
*
List of planet types
*
Lists of astronomical objects
References
{{DEFAULTSORT:Sub-Brown Dwarf
+
Types of planet
Planemos
Free-floating substellar objects