Brown dwarf

brown dwarfsbrown dwarvesPlanetarT-typeL-typevery low-mass brown dwarfBDblack dwarfbrown brown dwarf star
Brown dwarfs are substellar objects that occupy the mass range between the heaviest gas giant planets and the lightest stars, having masses between approximately 13 to 75–80 times that of Jupiter, or approximately 2.5 kg to about 1.5 kg.wikipedia
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Sub-brown dwarf

subfree planetsub-brown
Brown dwarfs are substellar objects that occupy the mass range between the heaviest gas giant planets and the lightest stars, having masses between approximately 13 to 75–80 times that of Jupiter, or approximately 2.5 kg to about 1.5 kg. Below this range are the sub-brown dwarfs (sometimes referred to as rogue planets), and above it are the lightest red dwarfs (M9 V).
A sub-brown dwarf or planetary-mass brown dwarf is an astronomical object that formed in the same manner as stars and brown dwarfs (i.e. through the collapse of a gas cloud) but that has a mass below the limiting mass for thermonuclear fusion of deuterium (about ).

Rogue planet

free-floating planetsfree-floating planetfree-floating planetary-mass object
Brown dwarfs are substellar objects that occupy the mass range between the heaviest gas giant planets and the lightest stars, having masses between approximately 13 to 75–80 times that of Jupiter, or approximately 2.5 kg to about 1.5 kg. Below this range are the sub-brown dwarfs (sometimes referred to as rogue planets), and above it are the lightest red dwarfs (M9 V).
Such objects have been ejected from the planetary system in which they formed or have never been gravitationally bound to any star or brown dwarf.

Substellar object

substellarsmaller solid objectssub-stellar object
Brown dwarfs are substellar objects that occupy the mass range between the heaviest gas giant planets and the lightest stars, having masses between approximately 13 to 75–80 times that of Jupiter, or approximately 2.5 kg to about 1.5 kg. Below this range are the sub-brown dwarfs (sometimes referred to as rogue planets), and above it are the lightest red dwarfs (M9 V).
This definition includes brown dwarfs and former stars similar to EF Eridani B, and can also include objects of planetary mass, regardless of their formation mechanism and whether or not they are associated with a primary star.

Luhman 16

Luhman 16 (WISE 1049-5319)Luhman 16B
At a distance of about 6.5 light years, the nearest known brown dwarf is Luhman 16, a binary system of brown dwarfs discovered in 2013. Since then, over 1,800 brown dwarfs have been identified, even some very close to Earth like Epsilon Indi Ba and Bb, a pair of brown dwarfs gravitationally bound to a Sun-like star 12 light-years from the Sun, and Luhman 16, a binary system of brown dwarfs at 6.5 light-years from the Sun.
Luhman 16 (WISE 1049−5319, WISE J104915.57−531906.1) is a binary brown-dwarf system in the southern constellation Vela at a distance of approximately 6.5 ly from the Sun.

2M1207b

2M1207 b
There are planets known to orbit brown dwarfs: 2M1207b, MOA-2007-BLG-192Lb, and 2MASS J044144b.
2M1207b is a planetary-mass object orbiting the brown dwarf 2M1207, in the constellation Centaurus, approximately 170 light-years from Earth.

Jupiter mass

M J mass of Jupitermass
Brown dwarfs are substellar objects that occupy the mass range between the heaviest gas giant planets and the lightest stars, having masses between approximately 13 to 75–80 times that of Jupiter, or approximately 2.5 kg to about 1.5 kg. Below this range are the sub-brown dwarfs (sometimes referred to as rogue planets), and above it are the lightest red dwarfs (M9 V).
It may also be used to describe the masses of brown dwarfs, as this unit provides a convenient scale for comparison.

Lithium burning

burnedfuse lithiumlithium-6 fusion
They are, however, thought to fuse deuterium ( 2 H) and to fuse lithium ( 7 Li) if their mass is above a debated threshold of and, respectively.
Lithium is generally present in brown dwarfs and not in low-mass stars.

MOA-2007-BLG-192Lb

b
There are planets known to orbit brown dwarfs: 2M1207b, MOA-2007-BLG-192Lb, and 2MASS J044144b.
The planet was discovered orbiting the brown dwarf or low-mass star MOA-2007-BLG-192L.

Jill Tarter

Dr. Jill TarterJill Cornell Tarter
In 1975, Jill Tarter suggested the term "brown dwarf", using "brown" as an approximate color.
It was in her PhD thesis where she coined the term "brown dwarf" while researching small-mass objects that fail to stably fuse hydrogen.

Teide 1

In 1995, the study of brown dwarfs changed substantially with the discovery of two indisputable substellar objects – Teide 1 and Gliese 229B – which were identified by the presence of the 670.8 nm lithium line.
Teide 1 was the first brown dwarf to be verified, in 1995.

Black dwarf

Sun will have cooled
The objects now called "brown dwarfs" were theorized to exist in the 1960s by Shiv S. Kumar and were originally called black dwarfs, a classification for dark substellar objects floating freely in space that were not massive enough to sustain hydrogen fusion. However: (a) the term black dwarf was already in use to refer to a cold white dwarf; (b) red dwarfs fuse hydrogen; and (c) these objects may be luminous at visible wavelengths early in their lives.
These objects are now generally called brown dwarfs, a term coined in the 1970s.

Stellar evolution

evolvedevolvingevolution
Early theories concerning the nature of the lowest-mass stars and the hydrogen-burning limit suggested that a population I object with a mass less than 0.07 solar masses or a population II object less than would never go through normal stellar evolution and would become a completely degenerate star.
These are known as brown dwarfs.

Epsilon Indi

ε IndEpsilon Indi Ba, Bbε Indi
Since then, over 1,800 brown dwarfs have been identified, even some very close to Earth like Epsilon Indi Ba and Bb, a pair of brown dwarfs gravitationally bound to a Sun-like star 12 light-years from the Sun, and Luhman 16, a binary system of brown dwarfs at 6.5 light-years from the Sun.
Epsilon Indi (ε Indi, ε Ind) is a star system approximately 12 light-years from Earth in the constellation of Indus consisting of a K-type main-sequence star, ε Indi A, and two brown dwarfs, ε Indi Ba and ε Indi Bb, in a wide orbit around it. The brown dwarfs were discovered in 2003.

List of exoplanet extremes

least massive planetlowest metallicity planet-bearing starmost distant known planet
HR 2562 b is listed as the most-massive known exoplanet (as of December 2017) in NASA's exoplanet archive, despite having a mass more than twice the 13-Jupiter-mass cutoff between planets and brown dwarfs.

Gas giant

gas giantsgiant planetJovian
Brown dwarfs are substellar objects that occupy the mass range between the heaviest gas giant planets and the lightest stars, having masses between approximately 13 to 75–80 times that of Jupiter, or approximately 2.5 kg to about 1.5 kg. Below this range are the sub-brown dwarfs (sometimes referred to as rogue planets), and above it are the lightest red dwarfs (M9 V).
The defining differences between a very low-mass brown dwarf and a gas giant (estimated at about 13 Jupiter masses) are debated.

HR 2562 b

HR 2562 b is listed as the most-massive known exoplanet (as of December 2017) in NASA's exoplanet archive, despite having a mass more than twice the 13-Jupiter-mass cutoff between planets and brown dwarfs.
Initially categorised as brown dwarf, its exact mass is unknown, and is thought to be 30 ± 15 Jupiter masses, and its luminosity is about two one-thousandths of a percent of a solar luminosity.

2MASS

2MASXTwo Micron All-Sky SurveyTwo Micron All-Sky Survey (2MASS)
GD 165B remained unique for almost a decade until the advent of the Two Micron All-Sky Survey (2MASS) which discovered many objects with similar colors and spectral features.
2MASS produced an astronomical catalog with over 300 million observed objects, including minor planets of the Solar System, brown dwarfs, low-mass stars, nebulae, star clusters and galaxies.

Kelvin–Helmholtz mechanism

gravitational contractionKelvin–Helmholtz heatingKelvin–Helmholtz timescale
As the cloud contracts it heats due to the Kelvin–Helmholtz mechanism.
This mechanism is evident on Jupiter and Saturn and on brown dwarfs whose central temperatures are not high enough to undergo nuclear fusion.

Stellar classification

spectral typeK-typeG-type
Stars are categorized by spectral class, with brown dwarfs designated as types M, L, T, and Y. Despite their name, brown dwarfs are of different colors.
Red dwarfs are a deep shade of orange, and brown dwarfs do not literally appear brown, but hypothetically would appear dim grey to a nearby observer.

White dwarf

white dwarfswhite dwarf starcentral star
However: (a) the term black dwarf was already in use to refer to a cold white dwarf; (b) red dwarfs fuse hydrogen; and (c) these objects may be luminous at visible wavelengths early in their lives.
They should not be confused with low-luminosity objects at the low-mass end of the main sequence, such as the hydrogen-fusing red dwarfs, whose cores are supported in part by thermal pressure, or the even lower-temperature brown dwarfs.

GD 165

In 1988, however, a faint companion to a star known as GD 165 was found in an infrared search of white dwarfs.
GD 165 is a system of a white dwarf and a brown dwarf of spectral types DA4 + L4, located in constellation Boötes at approximately 103 light-years from Earth.

Jupiter

Jovianplanet JupiterGiove
Like the Sun, Jupiter and Saturn are both made primarily of hydrogen and helium.
A "Jupiter mass" ( or ) is often used as a unit to describe masses of other objects, particularly extrasolar planets and brown dwarfs.

Thermonuclear fusion

thermonuclearfusingfusion
For most stars, gas and radiation pressure generated by the thermonuclear fusion reactions within the core of the star will support it against any further gravitational contraction.
The mass needed, however, is so great that gravitational confinement is only found in stars—the least massive stars capable of sustained fusion are red dwarfs, while brown dwarfs are able to fuse deuterium and lithium if they are of sufficient mass. In stars heavy enough, after the supply of hydrogen is exhausted in their cores, their cores (or a shell around the core) start fusing helium to carbon.

Lithium

Lilithium ionLi +
Lithium is generally present in brown dwarfs and not in low-mass stars.
Lithium is also found in brown dwarf substellar objects and certain anomalous orange stars.

WISE J031624.35+430709.1

T-class brown dwarfs, such as WISE 0316+4307, have been detected over 100 light-years from the Sun.
WISE J031624.35+430709.1 is a brown dwarf of spectral class T8, located in constellation Perseus at approximately 106 light-years from Earth.