Brown dwarf

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Infrared image showing two brown dwarfs in the binary system CFBDSIR 1458+10, obtained using the Laser Guide Star (LGS) Adaptive Optics system on the Keck II Telescope in Hawaii.

Brown dwarfs are substellar objects too low in mass to sustain hydrogen-1 fusion reactions in their cores, unlike main-sequence stars. They occupy the mass range between the heaviest gas giants and the lightest stars, with an upper limit around 75[1] to 80 Jupiter masses (MJ). Brown dwarfs heavier than about 13 MJ are thought to fuse deuterium and those above ~65 MJ, fuse lithium as well.[2]

The difference between a very-low-mass brown dwarf and a giant planet (~13 Jupiter masses) has been debated in a paper presented March of 2013.[3] A similar discussion involves DENIS-P J082303.1-491201 b, the lower-mass member of an ultracool binary system with a mass of nearly 29 Jupiter masses and listed as the most massive exoplanet yet found as of March 2014. Nonetheless, one school of thought is based on formation; another, on physics in the interior.[3]

Dwarfs are categorized by spectral classification, with the major types being M, L, T, and Y.[3] Despite their name, brown dwarfs are different colours.[3] Many brown dwarfs would likely appear magenta to the human eye according to A. J. Burgasser,[3] whereas another source has noted orange/red.[4] Brown dwarfs are not very luminous at visible wavelengths and in early studies Kumar called them black dwarfs, infrared dwarfs or red dwarfs. However the term black dwarf was already in use to refer to a cold White dwarf, red dwarfs fuse hydrogen, and brown dwarfs may be detectable at visible wavelengths early in their lives so Jill Tarter suggested the name 'brown dwarf' as an intermediate color between black and red.[5]

Another debate is whether brown dwarfs should have experienced fusion at some point in their history. Some planets are known to orbit brown dwarfs: 2M1207b, MOA-2007-BLG-192Lb, and 2MASS J044144b. Brown dwarfs may have fully convective surfaces and interiors, with no chemical differentiation by depth.[6]

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.


The smaller object is Gliese 229B, about 20 to 50 times the mass of Jupiter, orbiting the star Gliese 229. It is in the constellation Lepus, about 19 light years from Earth.

What became known as brown dwarfs were theorized to exist in the 1960s.[3]

Brown dwarfs, a term coined by Jill Tarter in 1975,[4][7] were originally called black dwarfs, a classification for dark substellar objects floating freely in space that were too low in mass to sustain hydrogen fusion. The term black dwarf currently refers to a white dwarf that has cooled to the point that it no longer emits significant light. Alternative names for brown dwarfs have been proposed, including planetar and substar.

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 0.09 solar masses would never go through normal stellar evolution and would become a completely degenerate star (Kumar 1963). The discovery of deuterium-burning down to 0.012 solar masses and the impact of dust formation in the cool outer atmospheres of brown dwarfs in the late 1980s brought these theories into question. However, such objects were hard to find because they emit almost no visible light. Their strongest emissions are in the infrared (IR) spectrum, and ground-based IR detectors were too imprecise at that time to readily identify any brown dwarfs.

Since then, numerous searches by various methods have sought to find these objects. These methods included multi-color imaging surveys around field stars, imaging surveys for faint companions to main-sequence dwarfs and white dwarfs, surveys of young star clusters, and radial velocity monitoring for close companions.

For many years, efforts to discover brown dwarfs were fruitless. In 1988, however, University of California, Los Angeles professors Eric Becklin and Ben Zuckerman identified a faint companion to a star known as GD 165 in an infrared search of white dwarfs. The spectrum of the companion GD 165B was very red and enigmatic, showing none of the features expected of a low-mass red dwarf star. It became clear that GD 165B would need to be classified as a much cooler object than the latest M dwarfs then known. GD 165B remained unique for almost a decade until the advent of the Two Micron All Sky Survey (2MASS) when Davy Kirkpatrick, of the California Institute of Technology, and others discovered many objects with similar colors and spectral features.

Today, GD 165B is recognized as the prototype of a class of objects now called "L dwarfs".[citation needed] Although the discovery of the coolest dwarf was highly significant at the time, it was debated whether GD 165B would be classified as a brown dwarf or simply a very-low-mass star, because observationally it is very difficult to distinguish between the two.[citation needed]

Soon after the discovery of GD 165B, other brown-dwarf candidates were reported. Most failed to live up to their candidacy, however, because the absence of lithium showed them to be stellar objects. True stars burn their lithium within a little over 100 Myr, whereas brown dwarfs (which can, confusingly, have temperatures and luminosities similar to true stars) will not. In other words, the detection of lithium in the atmosphere of a candidate object ensures that, as long as it is older than the relatively young age of 100 Myr, it is a brown dwarf.

In 1995, the study of brown dwarfs changed substantially with the discovery of two incontrovertible substellar objects (Teide 1 and Gliese 229B), which were identified by the presence of the 670.8 nm lithium line. The most notable of these objects was the latter, which was found to have a temperature and luminosity well below the stellar range. Remarkably, its near-infrared spectrum clearly exhibited a methane absorption band at 2 micrometres, a feature that had previously only been observed in the atmospheres of giant planets and that of Saturn's moon Titan. Methane absorption is not expected at the temperatures of main-sequence stars. This discovery helped to establish yet another spectral class even cooler than L dwarfs, known as "T dwarfs", for which Gliese 229B is the prototype.

The first confirmed brown dwarf was discovered by Spanish astrophysicists Rafael Rebolo (head of team), Maria Rosa Zapatero Osorio, and Eduardo Martín in 1994.[8] They called this object Teide 1 and it was found in the Pleiades open cluster. The discovery article was submitted to Nature in spring 1995, and published on September 14, 1995.[9] Nature highlighted "Brown dwarfs discovered, official" in the front page of that issue.

Teide 1 was discovered in images collected by the IAC team on January 6, 1994 using the 80 cm telescope (IAC 80) at Teide Observatory and its spectrum was first recorded in December 1994 using the 4.2 m William Herschel Telescope at Roque de los Muchachos Observatory (La Palma). The distance, chemical composition, and age of Teide 1 could be established because of its membership in the young Pleiades star cluster. Using the most advanced stellar and substellar evolution models at that moment, the team estimated for Teide 1 a mass 55 times the mass of Jupiter,[citation needed] which is clearly below the stellar-mass limit. The object became a reference in subsequent young brown dwarf related works.

In theory, a brown dwarf below 65 Jupiter masses is unable to burn lithium by thermonuclear fusion at any time during its evolution. This fact is one of the lithium test principles to examine the substellar nature in low-luminosity and low-surface-temperature astronomical bodies.

High-quality spectral data acquired by the Keck 1 telescope in November 1995 showed that Teide 1 had kept the initial lithium amount of the original molecular cloud from which Pleiades stars formed, proving the lack of thermonuclear fusion in its core. These observations confirmed that Teide 1 is a brown dwarf, as well as the efficiency of the spectroscopic lithium test.

For some time, Teide 1 was the smallest known object outside the Solar System that had been identified by direct observation. Since then, over 1,800 brown dwarfs have been identified,[10] even some very close to Earth like Epsilon Indi Ba and Bb, a pair of brown dwarfs gravitationally bound to a sunlike star around 12 light-years from the Sun, and Luhman 16, a binary system of brown dwarfs about 6.5 light-years away.


The standard mechanism for star birth is through the gravitational collapse of a cold interstellar cloud of gas and dust. As the cloud contracts it heats up from the release of gravitational potential energy. Early in the process the contracting gas quickly radiates away much of the energy, allowing the collapse to continue. Eventually, the central region becomes sufficiently dense to trap radiation. Consequently, the central temperature and density of the collapsed cloud increases dramatically with time, slowing the contraction, until the conditions are hot and dense enough for thermonuclear reactions to occur in the core of the protostar. 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. Hydrostatic equilibrium is reached and the star will spend most of its lifetime fusing hydrogen into helium as a main-sequence star.


  • 10\,\mathrm{g/cm^3} \,\lesssim\, \rho_c \,\lesssim\, 10^3\,\mathrm{{g}/{cm^{3}}}
  • T_c \lesssim 3 \times 10^6\,\mathrm{K}
  • P_c \sim 10^5\,\mathrm{Mbar}.

This means that the protostar is not massive enough and not dense enough to ever reach the conditions needed to sustain hydrogen fusion. The infalling matter is prevented, by electron degeneracy pressure, from reaching the densities and pressures needed.

Further gravitational contraction is prevented and the result is a "failed star", or brown dwarf that simply cools off by radiating away its internal thermal energy.

High-mass brown dwarfs vs low-mass stars[edit]

  • Lithium is generally present in brown dwarfs and not in low-mass stars. Stars, which achieve the high temperature necessary for fusing hydrogen, rapidly deplete their lithium. This occurs by a collision of lithium-7 and a proton producing two helium-4 nuclei. The temperature necessary for this reaction is just below the temperature necessary for hydrogen fusion. Convection in low-mass stars ensures that lithium in the whole volume of the star is depleted. Therefore, the presence of the lithium line in a candidate brown dwarf's spectrum is a strong indicator that it is indeed substellar. The use of lithium to distinguish candidate brown dwarfs from low-mass stars is commonly referred to as the lithium test, and was pioneered by Rafael Rebolo, Eduardo Martín and Antonio Magazzu. However, lithium is also seen in very young stars, which have not yet had enough time to burn it all. Heavier stars, like the Sun, can retain lithium in their outer atmospheres, which never get hot enough for lithium depletion, but those are distinguishable from brown dwarfs by their size. On the contrary, brown dwarfs at the high end of their mass range can be hot enough to deplete their lithium when they are young. Dwarfs of mass greater than 65 Jupiter masses can burn off their lithium by the time they are half a billion years old,[11] thus this test is not perfect.
  • Unlike stars, older brown dwarfs are sometimes cool enough that, over very long periods of time, their atmospheres can gather observable quantities of methane. Dwarfs confirmed in this fashion include Gliese 229B.
  • Main-sequence stars cool, but eventually reach a minimum bolometric luminosity that they can sustain through steady fusion. This varies from star to star, but is generally at least 0.01% that of the Sun.[citation needed] Brown dwarfs cool and darken steadily over their lifetimes: sufficiently old brown dwarfs will be too faint to be detectable.
  • Iron rain as part of atmospheric convection processes is possible only in brown dwarfs, and not in small stars. The spectroscopy research into iron rain is still ongoing—and not all brown dwarfs will always have this atmospheric anomaly. In 2013, a heterogeneous iron-containing atmosphere was imaged around the B component in the close Luhman 16 system.[12]

Low-mass brown dwarfs vs high-mass planets[edit]

An artistic concept of the brown dwarf around the star HD 29587, a companion known as HD 29587 B, and estimated to be about 55 Jupiter masses.

A remarkable property of brown dwarfs is that they are all roughly the same radius as Jupiter. At the high end of their mass range (60–90 Jupiter masses), the volume of a brown dwarf is governed primarily by electron-degeneracy pressure,[13] as it is in white dwarfs; at the low end of the range (10 Jupiter masses), their volume is governed primarily by Coulomb pressure, as it is in planets. The net result is that the radii of brown dwarfs vary by only 10–15% over the range of possible masses. This can make distinguishing them from planets difficult.



Gas giants have some of the characteristics of brown dwarfs. For example, Jupiter and Saturn are both made primarily of hydrogen and helium, like the Sun. Saturn is nearly as large as Jupiter, despite having only 30% the mass. Three of the giant planets in the Solar System (Jupiter, Saturn, and Neptune) emit much more heat than they receive from the Sun.[14] And all four giant planets have their own "planetary systems"—their moons. Brown dwarfs form independently, like stars, but lack sufficient mass to "ignite" as stars do. Like all stars, they can occur singly or in close proximity to other stars. Some orbit stars and can, like planets, have eccentric orbits.

Currently, the International Astronomical Union considers an object with a mass above the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) to be a brown dwarf, whereas an object under that mass (and orbiting a star or stellar remnant) is considered a planet.[15]

The 13 Jupiter-mass cutoff is a rule of thumb rather than something of precise physical significance. Larger objects will burn most of their deuterium and smaller ones will burn only a little, and the 13 Jupiter mass value is somewhere in between. The amount of deuterium burnt also depends to some extent on the composition of the object, specifically on the amount of helium and deuterium present and on the fraction of heavier elements, which determines the atmospheric opacity and thus the radiative cooling rate.[16]


A size comparison between our Sun, a young sub-brown dwarf, and Jupiter. As the sub-brown dwarf ages, it will gradually cool and shrink.

A sub-brown dwarf or planetary-mass brown dwarf is an astronomical object 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 13 Jupiter masses).[17] Some researchers call them free floating planets[18] while others call them planetary-mass brown dwarfs.[19]

Sub-brown dwarfs are formed in the manner of stars, 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.[20] Free-floating sub-brown dwarfs can be observationally indistinguishable from rogue planets that originally formed around a star and were ejected from orbit, and on the other hand a sub-brown dwarf formed free-floating in a star cluster may get captured into orbit around a star. 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.[21]

Lower mass limit[edit]

The smallest mass of gas cloud that could collapse to form a sub-brown dwarf is about 1 MJ.[22] This is because to collapse by gravitational contraction requires radiating away energy as heat and this is limited by the opacity of the gas.[23] A 3 MJ candidate is described in the paper.[24]

List of possible planetary-mass brown dwarfs[edit]

Orbiting one or more stars

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

Orbiting a brown dwarf

There is no consensus whether these companions of brown dwarfs should be considered sub-brown dwarfs or planets.



Classification of brown dwarfs[edit]

Spectral class M[edit]

Artist's vision of a late-M dwarf

There are brown dwarfs with a spectral class of M6.5 or later. They are also called late-M dwarfs.

Spectral class L[edit]

Artist's vision of an L-dwarf

The defining characteristic of spectral class M, the coolest type in the long-standing classical stellar sequence, is an optical spectrum dominated by absorption bands of titanium(II) oxide (TiO) and vanadium(II) oxide (VO) molecules. However, GD 165B, the cool companion to the white dwarf GD 165, had none of the hallmark TiO features of M dwarfs. The subsequent identification of many field counterparts to GD 165B ultimately led Kirkpatrick and others to the definition of a new spectral class, the L dwarfs, defined in the red optical region not by weakening metal-oxide bands (TiO, VO), but strong metal hydride bands (FeH, CrH, MgH, CaH) and prominent alkali metal lines (Na I, K I, Cs I, Rb I). As of 2013, over 900 L dwarfs have been identified,[10] most by wide-field surveys: the Two Micron All Sky Survey (2MASS), the Deep Near Infrared Survey of the Southern Sky (DENIS), and the Sloan Digital Sky Survey (SDSS).

Spectral class T[edit]

Artist's vision of a T-dwarf

As GD 165B is the prototype of the L dwarfs, Gliese 229B is the prototype of a second new spectral class, the T dwarfs. Whereas near-infrared (NIR) spectra of L dwarfs show strong absorption bands of H2O and carbon monoxide (CO), the NIR spectrum of Gliese 229B is dominated by absorption bands from methane (CH4), features that were only found in the giant planets of the Solar System and Titan. CH4, H2O, and molecular hydrogen (H2) collision-induced absorption (CIA) give Gliese 229B blue near-infrared colors. Its steeply sloped red optical spectrum also lacks the FeH and CrH bands that characterize L dwarfs and instead is influenced by exceptionally broad absorption features from the alkali metals Na and K. These differences led Kirkpatrick to propose the T spectral class for objects exhibiting H- and K-band CH4 absorption. As of 2013, 355 T dwarfs are known.[10] NIR classification schemes for T dwarfs have recently been developed by Adam Burgasser and Tom Geballe. Theory suggests that L dwarfs are a mixture of very-low-mass stars and sub-stellar objects (brown dwarfs), whereas the T dwarf class is composed entirely of brown dwarfs. Because of the absorption of sodium and potassium in the green part of the spectrum of T dwarfs, the actual appearance of T dwarfs to human visual perception is estimated to be not brown, but the color of magenta coal tar dye.[25][26] T-class brown dwarfs, such as WISE 0316+4307, have been detected over 100 light-years from the Sun.

Spectral class Y[edit]

Artist's vision of a Y-dwarf

There is some doubt as to what, if anything, should be included in the class Y dwarfs.[27][28] They are expected to be much cooler than T-dwarfs. They have been modelled,[29] though there is no well-defined spectral sequence yet with prototypes.

In 2009, the coolest known brown dwarfs had estimated effective temperatures between 500 and 600 K, and have been assigned the spectral class T9. Three examples are the brown dwarfs CFBDS J005910.90-011401.3, ULAS J133553.45+113005.2, and ULAS J003402.77−005206.7.[30] The spectra of these objects display absorption around 1.55 micrometers.[30] Delorme et al. have suggested that this feature is due to absorption from ammonia and that this should be taken as indicating the T–Y transition, making these objects of type Y0.[30][31] However, the feature is difficult to distinguish from absorption by water and methane,[30] and other authors have stated that the assignment of class Y0 is premature.[27]

In April 2010, two newly discovered ultracool sub-brown dwarfs (UGPS 0722-05 and SDWFS 1433+35[32]) were proposed as prototypes for spectral class Y0.

In February 2011, Luhman et al. reported the discovery of a ~300 K, 7-Jupiter-mass 'brown-dwarf' companion to a nearby white dwarf.[28] Though of 'planetary' mass, Rodriguez et al. suggest it is unlikely to have formed in the same manner as planets.[33]

Shortly after that, Liu et al. published an account of a "very cold" (~370 K) brown dwarf orbiting another very-low-mass brown dwarf and noted that "Given its low luminosity, atypical colors and cold temperature, CFBDS J1458+10B is a promising candidate for the hypothesized Y spectral class."[34]

In August 2011, scientists using data from NASA's Wide-field Infrared Survey Explorer (WISE) discovered six "Y dwarfs"—star-like bodies with temperatures as cool as the human body.[35][36]

WISE 0458+6434 is the first ultra-cool brown dwarf (green dot) discovered by WISE. The green and blue comes from infrared wavelengths mapped to visible colors.

WISE data has revealed hundreds of new brown dwarfs. Of these, fourteen are classified as cool Ys.[10] One of the Y dwarfs, called WISE 1828+2650, was, as of August 2011, the record holder for the coldest brown dwarf – emitting no visible light at all, this type of object resembles free-floating planets more than stars. WISE 1828+2650 was initially estimated to have an atmospheric temperature cooler than 300 K[37]—for comparison the upper end of room temperature is 298 K (25 °C, 80 °F). Its temperature has since been revised and newer estimates put it in the range of 250 to 400 K (−23–127 °C, −10–260 °F).[38]

In April 2014 WISE 0855–0714 was announced with a temperature profile estimated around 225 to 260 K and a mass of 3 to 10 MJ.[39] It was also unusual in that its observed parallax meant a distance close to 7.2±0.7 light years from the solar system.

Spectral and atmospheric properties of brown dwarfs[edit]

The majority of flux emitted by L and T dwarfs is in the 1 to 2.5 micrometre near-infrared range. Low and decreasing temperatures through the late M-, L-, and T-dwarf sequence result in a rich near-infrared spectrum containing a wide variety of features, from relatively narrow lines of neutral atomic species to broad molecular bands, all of which have different dependencies on temperature, gravity, and metallicity. Furthermore, these low temperature conditions favor condensation out of the gas state and the formation of grains.

Typical atmospheres of known brown dwarfs range in temperature from 2200 down to 750 K.[25] Compared to stars, which warm themselves with steady internal fusion, brown dwarfs cool quickly over time; more massive dwarfs cool slower than less massive ones.

Observational techniques[edit]

Estimated relative size of the planet Jupiter and brown dwarfs Gliese 229B and Teide 1




Brown dwarfs are often discovered in surveys to discover extrasolar planets. Methods of detecting extrasolar planets work for brown dwarfs as well, although brown dwarfs are much easier to detect.


First methane brown dwarf verified. Gliese 229B is discovered orbiting red dwarf Gliese 229A (20 ly away) using an adaptive optics coronagraph to sharpen images from the 60-inch (1.5 m) reflecting telescope at Palomar Observatory on Southern California's Mt. Palomar; follow-up infrared spectroscopy made with their 200-inch (5 m) Hale telescope shows an abundance of methane.
  • December 15, 1999: First X-ray flare detected from a brown dwarf. A team at the University of California monitoring LP 944-20 (60 Jupiter masses, 16 ly away) via the Chandra X-ray Observatory, catches a 2-hour flare.
  • 27 July 2000: First radio emission (in flare and quiescence) detected from a brown dwarf. A team of students at the Very Large Array reported their observations of LP 944-20 in the 15 March 2001 issue of the journal Nature.
  • 25 April 2014: Coldest known brown dwarf discovered. WISE J085510.83-071442.5 is 7.2 light-years away and has a temperature between -48 to -13 degrees Celsius, making the dwarf the 7th closest star to the sun. [NASA][40]

Brown dwarf as an X-ray source[edit]

Chandra image of LP 944-20 before flare and during flare

X-ray flares detected from brown dwarfs since 1999 suggest changing magnetic fields within them, similar to those in very-low-mass stars.

With no strong central nuclear energy source, the interior of a brown dwarf is in a rapid boiling, or convective state. When combined with the rapid rotation that most brown dwarfs exhibit, convection sets up conditions for the development of a strong, tangled magnetic field near the surface. The flare observed by Chandra from LP 944-20 could have its origin in the turbulent magnetized hot material beneath the brown dwarf's surface. A sub-surface flare could conduct heat to the atmosphere, allowing electric currents to flow and produce an X-ray flare, like a stroke of lightning. The absence of X-rays from LP 944-20 during the non-flaring period is also a significant result. It sets the lowest observational limit on steady X-ray power produced by a brown dwarf star, and shows that coronas cease to exist as the surface temperature of a brown dwarf cools below about 2800K and becomes electrically neutral.

Using NASA's Chandra X-ray Observatory, scientists have detected X-rays from a low-mass brown dwarf in a multiple star system.[41] This is the first time that a brown dwarf this close to its parent star(s) (Sun-like stars TWA 5A) has been resolved in X-rays.[41] "Our Chandra data show that the X-rays originate from the brown dwarf's coronal plasma which is some 3 million degrees Celsius", said Yohko Tsuboi of Chuo University in Tokyo.[41] "This brown dwarf is as bright as the Sun today in X-ray light, while it is fifty times less massive than the Sun", said Tsuboi.[41] "This observation, thus, raises the possibility that even massive planets might emit X-rays by themselves during their youth!"[41]

Recent developments[edit]

The brown dwarf Cha 110913-773444, located 500 light years away in the constellation Chamaeleon, may be in the process of forming a miniature planetary system. Astronomers from Pennsylvania State University have detected what they believe to be a disk of gas and dust similar to the one hypothesized to have formed the Solar System. Cha 110913-773444 is the smallest brown dwarf found to date (8 Jupiter masses), and if it formed a planetary system, it would be the smallest known object to have one. Their findings were published in the December 10, 2005 issue of Astrophysical Journal Letters.[42]


On January 8, 2013 astronomers using NASA's Hubble and Spitzer space telescopes probed the stormy atmosphere of a brown dwarf named 2MASS J22282889-431026, creating the most detailed "weather map" of a brown dwarf thus far. It shows wind-driven, planet-sized clouds. The new research is a stepping stone toward a better understanding not only brown dwarfs, but also of the atmospheres of planets beyond the Solar System.[43]

NASA's WISE mission has detected 200 new brown dwarfs.[44] There are actually fewer brown dwarfs in our cosmic neighborhood than previously thought. Rather than one star for every brown dwarf, there may be as many as six stars for every brown dwarf.[44]

Planets around brown dwarfs[edit]

Artist’s impression of the disc of dust and gas around a brown dwarf.[45]

The planetary-mass objects 2M1207b, GQ Lupi b and 2MASS J044144 that are orbiting brown dwarfs may have formed by cloud collapse rather than accretion and so may be sub-brown dwarfs rather than planets, which is inferred from relatively large masses and large orbits. However, in 2013, the first low-mass companion (OGLE-2012-BLG-0358L b) in a relatively small orbit was discovered orbiting a brown dwarf.[46]

Disks around brown dwarfs have been found to have many of the same features as disks around stars; therefore, it is expected that there will be accretion-formed planets around brown dwarfs.[47] Given the small mass of brown dwarf disks, most planets will be terrestrial planets rather than gas giants.[48] If a giant planet orbits a brown dwarf across our line of sight, then, because they have approximately the same diameter, this would give a large signal for detection by transit.[49] The accretion zone for planets around a brown dwarf is very close to the brown dwarf itself, so tidal forces would have a strong effect.[48]

Planets around brown dwarfs are likely to be carbon planets depleted of water.[50]

Superlative brown dwarfs[edit]

Main article: List of brown dwarfs
  • WD 0137-349 B: first confirmed brown dwarf to have survived the primary's red giant phase.[51]
  • In 1984, it was postulated by some astronomers that the Sun may be orbited by an undetected brown dwarf (sometimes referred to as Nemesis) that could interact with the Oort cloud just as passing stars can. But this theory has fallen out of favor.[52]
Table of Firsts
Brown Dwarfs
Title Brown Dwarf Name Spectral Type RA/Dec Constellation Notes
First discovered Teide 1 (Pleiades Open Star Cluster) M8 3h47m18.0s +24°22'31" Taurus Imaged in 1989 and 1994
First imaged with coronography Gliese 229 B T6.5 06h10m34.62s −21°51'52.1" Lepus Discovered 1994
First with planemo 2MASSW J1207334-393254 M8 12h07m33.47s −39°32'54.0" Centaurus
First with a planetary mass in orbit about it 2M1207 Planet discovered in 2004
First with a dust disk
First with bipolar outflow
First as a companion to a normal star Gliese 229 B T6.5 06h10m34.62s −21°51'52.1" Lepus 1995
First spectroscopic binary brown dwarf PPL 15 A, B [53] M6.5 Taurus Basri and Martin 1999
First eclipsing binary brown dwarf 2M0535-05 [54]


M6.5 Orion Stassun et al. 2006, 2007 (Distance ~450 pc)
First binary brown dwarf of T Type Epsilon Indi Ba, Bb [56] T1 + T6 Indus Distance: 3.626pc
First trinary brown dwarf DENIS-P J020529.0-115925 A/B/C L5, L8 and T0 02h05m29.40s −11°59'29.7" Cetus Delfosse et al. 1997, mentions
First L spectra
First T spectra Gliese 229 B T6.5 06h10m34.62s −21°51'52.1" Lepus 1995
Latest T spectrum ULAS J0034-00 T9[57] Cetus 2007
First Y spectrum CFBDS0059 – pending.[31] This is also classified as a T9 dwarf, due to its close resemblance to other T dwarfs[57] ~Y0 2008
First X-ray-emitting Cha Halpha 1 M8 Chamaeleon 1998
First X-ray flare LP 944-20 M9V 03h39m35.22s −35°25'44.1" Fornax 1999
First radio emission (in flare and quiescence) LP 944-20 M9V 03h39m35.22s −35°25'44.1" Fornax 2000

Table of Extremes
Brown Dwarfs
Title Brown Dwarf Name Spectral Type RA/Dec Constellation Notes
Metal-poor 2MASS J05325346+8246465 sdL7 05h32m53.46s +82°46'46.5" Gemini distance is ~10–30pc, metallicity is 0.1–0.01ZSol
Farthest WISP 0307-7243[58] T4.5 03h07m45.12s −72°43'57.5" Distance: 400pc
Nearest Luhman 16 Distance: ~6.5 ly
Brightest Teegarden's star M6.5 jmag=8.4
Dimmest WISE 1828+2650 Y2 jmag=23
Coolest WISE J085510.83-071442.5[59] Temperature -48 to -13 C
Most dense COROT-3b[60] Transiting brown dwarf COROT-3b has 22 MJ with a diameter 1.01±0.07 times that of Jupiter. It is slightly denser than osmium at standard conditions.
Least dense

See also[edit]


  2. ^ Nicholos Wethington (October 6, 2008). "Dense Exoplanet Creates Classification Calamity". Retrieved January 30, 2013. 
  3. ^ a b c d e f "A. J. Burgasser - Brown dwarfs: Failed stars, super Jupiters (2008)" (PDF). Retrieved 2013-03-16. 
  4. ^ a b Cain, Fraser (January 6, 2009). "If Brown Isn’t a Color, What Color are Brown Dwarfs?". Retrieved 24 September 2013. 
  5. ^ Brown Is Not a Color: Introduction of the Term ‘Brown Dwarf’, Chapter in "50 Years of Brown Dwarfs", Springer, 2013, ISBN 3319011626, Jill Tarter
  6. ^ Ian O'Neill (Sep 13, 2011). "Violent Storms Rage on Nearby Brown Dwarf". Retrieved January 30, 3013. 
  7. ^ Planet Quest: The Epic Discovery of Alien Solar Systems, Ken Croswell, Oxford University Press, 1999, ISBN 9780192880833, pages 118–119
  8. ^ "Instituto de Astrofísica de Canarias, IAC". Retrieved 2013-03-16. 
  9. ^ "Discovery of a brown dwarf in the Pleiades star cluster". 1995-09-14. Retrieved 2013-03-16. 
  10. ^ a b c d Davy Kirkpatrick; Adam Burgasser (6 November 2012). " Photometry, spectroscopy, and astrometry of M, L, and T dwarfs". Retrieved 2012-12-28.  (M=536, L=918, T=355, Y=14)
  11. ^ Kulkarni, S. R. (30 May 1997). "Brown Dwarfs: A Possible Missing Link Between Stars and Planets". Vol. 276. Science Magazine. Retrieved 25 April 2013. 
  12. ^ [1]
  13. ^ Gibor Basri; Brown (2006-08-20). "Planetesimals to Brown Dwarfs: What is a Planet?". Ann.Rev.Earth Planet.Sci. 34: 193–216. arXiv:astro-ph/0608417. Bibcode:2006AREPS..34..193B. doi:10.1146/ 
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