Brown dwarf
Brown dwarfs are
Astronomers classify self-luminous objects by spectral type, a distinction intimately tied to the surface temperature, and brown dwarfs occupy types M, L, T, and Y.[4][5] As brown dwarfs do not undergo stable hydrogen fusion, they cool down over time, progressively passing through later spectral types as they age.
Their name comes not from the color of light they emit but from their falling between
Though their existence was initially theorized in the 1960s, it was not until the mid-1990s that the first unambiguous brown dwarfs were discovered. As brown dwarfs have relatively low surface temperatures, they are not very bright at visible wavelengths, emitting most of their light in the infrared. However, with the advent of more capable infrared detecting devices, thousands of brown dwarfs have been identified. The nearest known brown dwarfs are located in the Luhman 16 system, a binary of L- and T-type brown dwarfs about 6.5 light-years (2.0 parsecs) from the Sun. Luhman 16 is the third closest system to the Sun after Alpha Centauri and Barnard's Star.
History
Early theorizing
The objects now called "brown dwarfs" were theorized by Shiv S. Kumar in the 1960s to exist and were originally called black dwarfs,[9] 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. Because of this, alternative names for these objects were proposed, including planetar and substar. In 1975, Jill Tarter suggested the term "brown dwarf", using "brown" as an approximate color.[6][10][11]
The term "black dwarf" still refers to a white dwarf that has cooled to the point that it no longer emits significant amounts of light. However, the time required for even the lowest-mass white dwarf to cool to this temperature is calculated to be longer than the current age of the universe; hence such objects are expected to not yet exist.[12]
Early theories concerning the nature of the lowest-mass stars and the
Deuterium fusion
The discovery of
Since then, numerous searches by various methods have sought these objects. These methods included multi-color imaging surveys around field stars, imaging surveys for faint companions of
GD 165B and class L
For many years, efforts to discover brown dwarfs were fruitless. In 1988, however, a faint companion to the white dwarf star GD 165 was found 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. 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) in 1997, which 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".[16][17]
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
Gliese 229B and class T
The first class "T" brown dwarf was discovered in 1994 by
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 any temperature of a main-sequence star. 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.
Teide 1 and class M
The first confirmed class "M" brown dwarf was discovered by Spanish astrophysicists
Teide 1 was discovered in images collected by the IAC team on 6 January 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 of 55 ± 15 MJ,[22] which is below the stellar-mass limit. The object became a reference in subsequent young brown dwarf related works.
In theory, a brown dwarf below 65 MJ is unable to burn lithium by thermonuclear fusion at any time during its evolution. This fact is one of the lithium test principles used to judge the substellar nature of 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 still had the initial lithium abundance 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,[23] 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,[24] and Luhman 16, a binary system of brown dwarfs at 6.5 light-years from the Sun.
Theory
This section needs additional citations for verification. (July 2020) |
The standard mechanism for
If, however, the initial
This means that the protostar is not massive or dense enough ever to 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 brown dwarf that simply cools off by radiating away its internal thermal energy. Note that, in principle, it is possible for a brown dwarf to slowly accrete mass above the
High-mass brown dwarfs versus low-mass stars
nuclei. The temperature necessary for this reaction is just below that necessary for hydrogen fusion. Convection in low-mass stars ensures that lithium in the whole volume of the star is eventually depleted. Therefore, the presence of the lithium spectral line in a candidate brown dwarf is a strong indicator that it is indeed a substellar object.The lithium test
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 also retain lithium in their outer layers, which never get hot enough to fuse lithium, and whose convective layer does not mix with the core where the lithium would be rapidly depleted. Those larger stars are easily distinguishable from brown dwarfs by their size and luminosity.
Conversely, 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 MJ can burn their lithium by the time they are half a billion years old;[27] thus the lithium test is not perfect.
Atmospheric methane
Unlike stars, older brown dwarfs are sometimes cool enough that, over very long periods of time, their atmospheres can gather observable quantities of methane, which cannot form in hotter objects. Dwarfs confirmed in this fashion include Gliese 229B.
Iron, silicate and sulfide clouds
Main-sequence stars cool, but eventually reach a minimum
Clouds are used to explain the weakening of the iron hydride (FeH) spectral line in late L-dwarfs. Iron clouds deplete FeH in the upper atmosphere, and the cloud layer blocks the view to lower layers still containing FeH. The later strengthening of this chemical compound at cooler temperatures of mid- to late T-dwarfs is explained by disturbed clouds that allows a telescope to look into the deeper layers of the atmosphere that still contains FeH.[28] Young L/T-dwarfs (L2-T4) show high variability, which could be explained with clouds, hot spots, magnetically driven aurorae or thermochemical instabilities.[29] The clouds of these brown dwarfs are explained as either iron clouds with varying thickness or a lower thick iron cloud layer and an upper silicate cloud layer. This upper silicate cloud layer can consist out of quartz, enstatite, corundum and/or fosterite.[30][31] It is however not clear if silicate clouds are always necessary for young objects.[32] Silicate absorption can be directly observed in the mid-infrared at 8 to 12 μm. Observations with Spitzer IRS have shown that silicate absorption is common, but not ubiquitous, for L2-L8 dwarfs.[33] Additionally, MIRI has observed silicate absorption in the planetary-mass companion VHS 1256b.[34]
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, but 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 nearby Luhman 16 system.[35]
For late T-type brown dwarfs only a few variable searches were carried out. Thin cloud layers are predicted to form in late T-dwarfs from chromium and potassium chloride, as well as several sulfides. These sulfides are manganese sulfide, sodium sulfide and zinc sulfide.[36] The variable T7 dwarf 2M0050–3322 is explained to have a top layer of potassium chloride clouds, a mid layer of sodium sulfide clouds and a lower layer of manganese sulfide clouds. Patchy clouds of the top two cloud layers could explain why the methane and water vapor bands are variable.[37]
At the lowest temperatures of the Y-dwarf WISE 0855-0714 patchy cloud layers of sulfide and water ice clouds could cover 50% of the surface.[38]
Low-mass brown dwarfs versus high-mass planets
Like stars, brown dwarfs form independently, but, unlike stars, they lack sufficient mass to "ignite" hydrogen fusion. Like all stars, they can occur singly or in close proximity to other stars. Some orbit stars and can, like planets, have eccentric orbits.
Size and fuel-burning ambiguities
Brown dwarfs are all roughly the same radius as Jupiter. At the high end of their mass range (60–90 MJ), the volume of a brown dwarf is governed primarily by electron-degeneracy pressure,[39] as it is in white dwarfs; at the low end of the range (10 MJ), 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. Moreover, the mass–radius relationship shows no change from about one Saturn mass to the onset of hydrogen burning (0.080±0.008 M☉), suggesting that from this perspective brown dwarfs are simply high-mass Jovian planets.[40] This can make distinguishing them from planets difficult.
In addition, many brown dwarfs undergo no fusion; even those at the high end of the mass range (over 60 MJ) cool quickly enough that after 10 million years they no longer undergo
Heat spectrum
X-ray and infrared spectra are telltale signs of brown dwarfs. Some emit X-rays; and all "warm" dwarfs continue to glow tellingly in the red and infrared spectra until they cool to planet-like temperatures (under 1,000 K).
Gas giants have some of the characteristics of brown dwarfs. Like the Sun, Jupiter and Saturn are both made primarily of hydrogen and helium. 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 (up to about twice) heat than they receive from the Sun.[41][42] All four giant planets have their own "planetary" systems, in the form of extensive moon systems.
Current IAU standard
Currently, the International Astronomical Union considers an object above 13 MJ (the limiting mass for thermonuclear fusion of deuterium) to be a brown dwarf, whereas an object under that mass (and orbiting a star or stellar remnant) is considered a planet. The minimum mass required to trigger sustained hydrogen burning (about 80 MJ) forms the upper limit of the definition.[3][43]
It is also debated whether brown dwarfs would be better defined by their formation process rather than by theoretical mass limits based on nuclear fusion reactions.
The 13-Jupiter-mass cutoff is a rule of thumb rather than a quantity with 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.[44] 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.[45]
As of 2011 the Extrasolar Planets Encyclopaedia included objects up to 25 Jupiter masses, saying, "The fact that there is no special feature around 13 MJup in the observed mass spectrum reinforces the choice to forget this mass limit".[46] As of 2016, this limit was increased to 60 Jupiter masses,[47] based on a study of mass–density relationships.[48]
The Exoplanet Data Explorer includes objects up to 24 Jupiter masses with the advisory: "The 13 Jupiter-mass distinction by the IAU Working Group is physically unmotivated for planets with rocky cores, and observationally problematic due to the sin i ambiguity."[49] The NASA Exoplanet Archive includes objects with a mass (or minimum mass) equal to or less than 30 Jupiter masses.[50]
Sub-brown dwarf
Objects below 13 MJ, called sub-brown dwarfs or planetary-mass brown dwarfs, form in the same manner as stars and brown dwarfs (i.e. through the collapse of a gas cloud) but have a mass below the limiting mass for thermonuclear fusion of deuterium.[51]
Some researchers call them free-floating planets,[52] whereas others call them planetary-mass brown dwarfs.[53]
Role of other physical properties in the mass estimate
While spectroscopic features can help to distinguish between
−0.8 MJ.[58]
Observations
Classification of brown dwarfs
Spectral class M
These are brown dwarfs with a spectral class of M5.5 or later; they are also called late-M dwarfs. Some scientists regard them as red dwarfs.[citation needed] All brown dwarfs with spectral type M are young objects, such as Teide 1, which is the first M-type brown dwarf discovered, and LP 944-20, the closest M-type brown dwarf.
Spectral class L
The defining characteristic of
Spectral class T
As GD 165B is the prototype of the L dwarfs,
Spectral class Y
In 2009, the coolest-known brown dwarfs had estimated effective temperatures between 500 and 600 K (227–327 °C; 440–620 °F), 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.[62] The spectra of these objects have absorption peaks around 1.55 micrometres.[62] 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.[62][63] However, the feature is difficult to distinguish from absorption by water and methane,[62] and other authors have stated that the assignment of class Y0 is premature.[64]
The first JWST spectral energy distribution of a Y-dwarf was able to observe several bands of molecules in the atmosphere of the Y0-dwarf WISE 0359−5401. The observations covered spectroscopy from 1 to 12 μm and photometry at 15, 18 and 21 μm. The molecules water (H2O), methane (CH4), carbon monoxide (CO), carbon dioxide (CO2) and ammonia (NH3) were detected in WISE 0359−5401. Many of these features have been observed before in this Y-dwarf and warmer T-dwarfs by other observatories, but JWST was able to observe them in a single spectrum. Methane is the main reservoir of carbon in the atmosphere of WISE 0359−5401, but there is still enough carbon left to form detectable carbon monoxide (at 4.5–5.0 μm) and carbon dioxide (at 4.2–4.35 μm) in the Y-dwarf. Ammonia was difficult to detect before JWST, as it blends in with the absorption feature of water in the near-infrared, as well at 5.5–7.1 μm. At longer wavelengths of 8.5–12 μm the spectrum of WISE 0359−5401 is dominated by the absorption of ammonia. At 3 μm there is an additional newly detected ammonia feature.[65]
Colder lower atmosphere
Usually brown dwarfs have a pressure–temperature (P–T) profile in an adiabatic form, which means that the pressure and temperature increase with depth. JWST spectroscopy and photometry suggest that Y-dwarfs have P–T profiles that are not in the standard adiabatic form. This means that upper layers of the atmosphere have a warmer temperature and lower layers of the atmosphere have a colder temperature. This is explained with the rapid rotation of these isolated objects. The rapid rotation leads to dynamical, thermal, and chemical changes, which disrupt the convective transport of heat from the lower to the upper atmosphere. This different P–T profile influences the shape of the spectrum and influences the composition of carbon- and nitrogen-bearing molecules in the atmosphere of Y-dwarfs.[66]
Individual Y-dwarf discoveries
Timeline of Y-dwarf discoveries:
- April 2010: Two newly discovered ultracool sub-brown dwarfs (UGPS 0722-05 and SDWFS 1433+35) were proposed as prototypes for spectral class Y0.[67]
- February 2011: Luhman et al. reported the discovery of WD 0806−661 B, a brown dwarf companion to a nearby white dwarf, with a temperature of c. 300 K (27 °C; 80 °F) and mass of 7 MJ.[68] Though of planetary mass, Rodriguez et al. suggest it is unlikely to have formed in the same manner as planets.[69]
- February 2011: Shortly after that, Liu et al. published an account of a "very cold" (c. 370 K (97 °C; 206 °F)) brown dwarf orbiting another very-low-mass brown dwarf and noted, "Given its low luminosity, atypical colors and cold temperature, CFBDS J1458+10B is a promising candidate for the hypothesized Y spectral class."[70]
- August 2011: Scientists using data from NASA's Wide-field Infrared Survey Explorer (WISE) discovered six objects that they classified as Y dwarfs with temperatures as cool as 25 °C (298 K; 77 °F).[71][72] These were published in two papers.[73][74]
- July 2012: Seven new Y-dwarfs were discovered, making the total number of confirmed Y-dwarfs fourteen.[75][23] 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 a free-floating planet more than a star. WISE 1828+2650 was initially estimated to have an atmospheric temperature cooler than 300 K (27 °C; 80 °F).[76] Its temperature has since been revised, and newer estimates put it in the range of 250 to 400 K (−23 to 127 °C; −10 to 260 °F).[77]
- November 2012: WISE J1639−6847 was discovered. As of February 2024 it was the second-closest known Y-dwarf to Earth.[78]
- April 2014: WISE 0855−0714 was announced, with a temperature profile estimated around 225 to 260 K (−48 – −13 °C; −55–8 °F) and a mass of 3 to 10 MJ.[79] It was also unusual in that its observed parallax meant a distance close to 7.2 ± 0.7 light-years from the Solar System.
- May 2014: The Y-dwarf WISE J2209+2711 was published.[80]
- November 2014: The object WISEA J1141−3326 was estimated to be a Y-dwarf[81] and it was later confirmed.[82]
- April 2015: The T+Y dwarf binary WISE J0146+4234 AB was discovered.[83]
- May 2015: Three Y-dwarfs were discovered with Hubble, bringing the total number of confirmed Y-dwarfs to 21.[84]
- June 2018: WISEA J0302−5817 was published as a Y-dwarf, and WISEA J1141−3326 was confirmed as a Y-dwarf.[82]
- August 2019: A search of the CatWISE catalog revealed CWISEP J1935-1546, one of the coldest brown dwarfs with an estimated temperature of 270 to 360 K (−3–87 °C; 26–188 °F).[85] In 2023 it was announced that CWISEP J1935-1546 had methane emission due to an aurora.[86]
- January 2020: In January 2020 the discovery of WISE J0830+2837, initially discovered by citizen scientists of the Backyard Worlds project, was presented at the 235th meeting of the American Astronomical Society. This Y dwarf is 36.5 light-years distant from the Solar System and has a temperature of about 350 K (77 °C; 170 °F).[87]
- February 2020: The CatWISE catalog combined NASA's WISE and NEOWISE surveys.[88] It expanded the number of faint sources and has therefore been used to find the faintest brown dwarfs, including Y dwarfs. Seventeen candidate Y dwarfs were discovered by the CatWISE researchers. Initial color with the Spitzer Space Telescope indicated that CW1446 is one of the reddest and coldest Y dwarfs.[89] Additional data with Spitzer showed that CW1446 is the fifth-reddest brown dwarf, with a temperature of about 310 to 360 K (37–87 °C; 98–188 °F) and a distance of about 10 parsecs.[55]
- August 2020: Five candidate Y-dwarfs were discovered via the Backyard Worlds project.[90]
- April 2021: New Y-dwarf candidates were published by the CatWISE and Backyard Worlds teams in a collaborative paper.[91]
- August 2021: Ross 19B, an old object near the T/Y-boundary orbiting an M-dwarf, was discovered by the Backyard Worlds team.[92]
- April 2023: WISE J0336−0143 was confirmed as a Y-dwarf binary with JWST.[93] The B secondary is likely one of the coldest confirmed Y-dwarfs as of December 2023, with an estimated temperature of 246 to 404 K (−27–131 °C; −17–268 °F).[94]
- November 2023: CWISE J1055+5443, an object previously classified as a T-dwarf, was confirmed as a nearby Y-dwarf.[95]
- December 2023: Three new Y-dwarf candidates were published.[94] The total number of confirmed Y-dwarfs was 27, and 30 additional Y-dwarf candidates existed as of February 2024.
- January 2024: Two candidate planets orbiting white dwarfs were discovered with JWST. If spectroscopically confirmed they would likely be Y-dwarfs due to their cold estimated temperature (Teff<200 K).[96]
Role of vertical mixing
In the hydrogen-dominated atmosphere of brown dwarfs a chemical equilibrium between carbon monoxide and methane exists. Carbon monoxide reacts with hydrogen molecules and forms methane and hydroxyl in this reaction. The hydroxyl radical might later react with hydrogen and form water molecules. In the other direction of the reaction, methane reacts with hydroxyl and forms carbon monoxide and hydrogen. The chemical reaction is tilted towards carbon monoxide at higher temperatures (L-dwarfs) and lower pressure. At lower temperatures (T-dwarfs) and higher pressure the reaction is tilted towards methane, and methane predominates at the T/Y-boundary. However, vertical mixing of the atmosphere can cause methane to sink into lower layers of the atmosphere and carbon monoxide to rise from these lower and hotter layers. The carbon monoxide is slow to react back into methane because of an energy barrier that prevents the breakdown of the C-O bonds. This forces the observable atmosphere of a brown dwarf to be in a chemical disequilibrium. The L/T transition is mainly defined with the transition from a carbon-monoxide-dominated atmosphere in L-dwarfs to a methane-dominated atmosphere in T-dwarfs. The amount of vertical mixing can therefore push the L/T-transition to lower or higher temperatures. This becomes important for objects with modest surface gravity and extended atmospheres, such as giant exoplanets. This pushes the L/T transition to lower temperatures for giant exoplanets. For brown dwarfs this transition occurs at around 1200 K. The exoplanet HR 8799c, on the other hand, does not show any methane, while having a temperature of 1100K.[97]
The transition between T- and Y-dwarfs is often defined as 500 K because of the lack of spectral observations of these cold and faint objects.[98] Future observations with JWST and the ELTs might improve the sample of Y-dwarfs with observed spectra. Y-dwarfs are dominated by deep spectral features of methane, water vapor and possibly absorption features of ammonia and water ice.[98] Vertical mixing, clouds, metallicity, photochemistry, lightning, impact shocks and metallic catalysts might influence the temperature at which the L/T and T/Y transition occurs.[97]
Secondary features
Secondary features | |
---|---|
pec | This suffix (e.g. L2pec) stands for "peculiar".[99] |
sd | This prefix (e.g. sdL0) stands for subdwarf and indicates a low metallicity and blue color[100] |
β | Objects with the beta (β) suffix (e.g. L4β) have an intermediate surface gravity.[101] |
γ | Objects with the gamma (γ) suffix (e.g. L5γ) have a low surface gravity.[101] |
red | The red suffix (e.g. L0red) indicates objects without signs of youth, but high dust content[102] |
blue | The blue suffix (e.g. L3blue) indicates unusual blue near-infrared colors for L dwarfs without obvious low metallicity[103] |
Young brown dwarfs have low
Spectral and atmospheric properties of brown dwarfs
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 2,200 down to 750 K.[60] Compared to stars, which warm themselves with steady internal fusion, brown dwarfs cool quickly over time; more massive dwarfs cool more slowly than less massive ones. There is some evidence that the cooling of brown dwarfs slows down at the transition between spectral classes L and T (about 1000 K).[107]
Observations of known brown dwarf candidates have revealed a pattern of brightening and dimming of infrared emissions that suggests relatively cool, opaque cloud patterns obscuring a hot interior that is stirred by extreme winds. The weather on such bodies is thought to be extremely strong, comparable to but far exceeding Jupiter's famous storms.
On January 8, 2013, astronomers using NASA's Hubble and Spitzer space telescopes probed the stormy atmosphere of a brown dwarf named 2MASS J22282889–4310262, 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.[108]
In April 2020 scientists reported clocking wind speeds of +650 ± 310 metres per second (up to 1,450 miles per hour) on the nearby brown dwarf 2MASS J10475385+2124234. To calculate the measurements, scientists compared the rotational movement of atmospheric features, as ascertained by brightness changes, against the electromagnetic rotation generated by the brown dwarf's interior. The results confirmed previous predictions that brown dwarfs would have high winds. Scientists are hopeful that this comparison method can be used to explore the atmospheric dynamics of other brown dwarfs and extrasolar planets.[109]
Observational techniques
Coronagraphs have recently been used to detect faint objects orbiting bright visible stars, including Gliese 229B.
Sensitive telescopes equipped with charge-coupled devices (CCDs) have been used to search distant star clusters for faint objects, including Teide 1.
Wide-field searches have identified individual faint objects, such as Kelu-1 (30 light-years away).
Brown dwarfs are often discovered in surveys to discover exoplanets. Methods of detecting exoplanets work for brown dwarfs as well, although brown dwarfs are much easier to detect.
Brown dwarfs can be powerful emitters of radio emission due to their strong magnetic fields. Observing programs at the Arecibo Observatory and the Very Large Array have detected over a dozen such objects, which are also called ultracool dwarfs because they share common magnetic properties with other objects in this class.[110] The detection of radio emission from brown dwarfs permits their magnetic field strengths to be measured directly.
Milestones
- 1995: First brown dwarf verified. Teide 1, an M8 object in the Pleiades cluster, is picked out with a CCD in the Spanish Observatory of Roque de los Muchachos of the Instituto de Astrofísica de Canarias.
- First methane brown dwarf verified. Gliese 229B is discovered orbiting red dwarf Mount Palomar; follow-up infrared spectroscopy made with their 200-inch (5.1 m) Hale Telescopeshows an abundance of methane.
- 1998: First X-ray-emitting brown dwarf found. Cha Helpha 1, an M8 object in the Chamaeleon I dark cloud, is determined to be an X-ray source, similar to convective late-type stars.
- 15 December 1999: First X-ray flare detected from a brown dwarf. A team at the University of California monitoring LP 944-20 (60 MJ, 16 ly away) via the Chandra X-ray Observatory, catches a 2-hour flare.[111]
- 27 July 2000: First radio emission (in flare and quiescence) detected from a brown dwarf. A team of students at the Very Large Array detected emission from LP 944–20.[112]
- 30 April 2004: First detection of a candidate exoplanet around a brown dwarf: 2M1207b discovered with the VLT and the first directly imaged exoplanet.[113]
- 20 March 2013: Discovery of the closest brown dwarf system: Luhman 16.[114]
- 25 April 2014: Coldest-known brown dwarf discovered. WISE 0855−0714 is 7.2 light-years away (seventh-closest system to the Sun) and has a temperature between −48 and −13 °C.[79]
Brown dwarf as an X-ray source
X-ray flares detected from brown dwarfs since 1999 suggest changing
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, and shows that coronas cease to exist as the surface temperature of a brown dwarf cools below about 2,800 K 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.[115] 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.[115] "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.[115] "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.[115] "This observation, thus, raises the possibility that even massive planets might emit X-rays by themselves during their youth!"[115]
Brown dwarfs as radio sources
The first brown dwarf that was discovered to emit radio signals was LP 944-20, which was observed based on its X-ray emission. Approximately 5–10% of brown dwarfs appear to have strong magnetic fields and emit radio waves, and there may be as many as 40 magnetic brown dwarfs within 25 pc of the Sun based on Monte Carlo modeling and their average spatial density.[116] The power of the radio emissions of brown dwarfs is roughly constant despite variations in their temperatures.[110] Brown dwarfs may maintain magnetic fields of up to 6 kG in strength.[117] Astronomers have estimated brown dwarf magnetospheres to span an altitude of approximately 107 m given properties of their radio emissions.[118] It is unknown whether the radio emissions from brown dwarfs more closely resemble those from planets or stars. Some brown dwarfs emit regular radio pulses, which are sometimes interpreted as radio emission beamed from the poles, but may also be beamed from active regions. The regular, periodic reversal of radio wave orientation may indicate that brown dwarf magnetic fields periodically reverse polarity. These reversals may be the result of a brown dwarf magnetic activity cycle, similar to the solar cycle.[119]
Recent developments
Estimates of brown dwarf populations in the solar neighbourhood suggest that there may be as many as six stars for every brown dwarf.[121] A more recent estimate from 2017 using the young massive star cluster RCW 38 concluded that the Milky Way galaxy contains between 25 and 100 billion brown dwarfs.[122] (Compare these numbers to the estimates of the number of stars in the Milky Way; 100 to 400 billion.)
In a study published in Aug 2017 NASA's Spitzer Space Telescope monitored infrared brightness variations in brown dwarfs caused by cloud cover of variable thickness. The observations revealed large-scale waves propagating in the atmospheres of brown dwarfs (similarly to the atmosphere of Neptune and other Solar System giant planets). These atmospheric waves modulate the thickness of the clouds and propagate with different velocities (probably due to differential rotation).[123]
In August 2020, astronomers discovered 95 brown dwarfs near the Sun through the project Backyard Worlds: Planet 9.[124]
Binary brown dwarfs
Brown dwarf-Brown dwarf binaries
Brown dwarfs binaries of type M, L, and T are less common with a lower mass of the primary.[125] L-dwarfs have a binary fraction of about 24+6
−2% and the binary fraction for late T, early Y-dwarfs (T5-Y0) is about 8±6%.[126]
Brown dwarf binaries have a higher companion-to-host ratio for lower mass binaries. Binaries with a M-type star as a primary have for example a broad distribution of q with a preference of q≥0.4. Brown dwarfs on the other hand show a strong preference for q≥0.7. The separation is decreasing with mass: M-type stars have a separation peaking at 3-30 astronomical units (au), M-L-type brown dwarfs have a projected separation peaking at 5-8 au and T5-Y0 objects have a projected separation that follows a lognormal distribution with a peak separation of about 2.9 au.[126]
An example is the closest brown dwarf binary Luhman 16 AB with a primary L7.5 dwarf and a separation of 3.5 au and q=0.85. The separation is on the lower end of the expected separation for M-L-type brown dwarfs, but the mass ratio is typical.
It is not known if the same trend continues with Y-dwarfs, because their sample size is so small. The Y+Y dwarf binaries should have a high mass ratio q and a low separation, reaching scales of less than one au.[127] The Y+Y dwarf WISE J0336-0143 was recently confirmed as a binary with JWST and it has a mass ratio of q=0.62±0.05 and a separation of 0.97 astronomical units. The researchers point out that the sample size of low-mass binary brown dwarfs is too small to determine if WISE J0336-0143 is a typical representative of low-mass binaries or a peculiar system.[93]
Observations of the orbit of binary systems containing brown dwarfs can be used to measure the mass of the brown dwarf. In the case of 2MASSW J0746425+2000321, the secondary weighs 6% of the solar mass. This measurement is called a dynamical mass.[128][129] The brown dwarf system closest to the Solar System is the binary Luhman 16. It was attempted to search for planets around this system with a similar method, but none were found.[130]
Unusual brown dwarf binaries
The wide binary system
More recently the wide binary
There are other interesting binary systems such as the
Brown dwarfs around stars
Brown dwarfs and massive planets in a close orbit (less than 5 au) around stars are rare and this is sometimes described as the brown dwarf desert. Less than 1% of stars with the mass of the sun have a brown dwarf within 3-5 au.[136]
An example for a star-brown dwarf binary is the first discovered T-dwarf Gliese 229 B, which orbits around the main-sequence star Gliese 229 A, a red dwarf. Brown dwarfs orbiting subgiants are also known, such as TOI-1994b which orbits its star every 4.03 days.[137]
There is also disagreement if some low-mass brown dwarfs should be considered planets. The NASA Exoplanet archive includes brown dwarfs with a minimum mass less or equal to 30 Jupiter masses as planets as long as there are other criteria fulfilled (e.g. orbiting a star).[138] The Working Group on Extrasolar Planets (WGESP) of the IAU on the other hand only considers planets with a mass below 13 Jupiter masses.[139]
White dwarf–brown dwarf binaries
Brown dwarfs around white dwarfs are quite rare. GD 165 B, the prototype of the L dwarfs, is one such system.[140] Such systems can be useful in determining the age of the system and the mass of the brown dwarf. Other white dwarf-brown dwarf binaries are COCONUTS-1 AB (7 billion years old),[58] and LSPM J0055+5948 AB (10 billion years old),[90] SDSS J22255+0016 AB (2 billion years old)[141] WD 0806−661 AB (1.5–2.7 billion years old).[142]
Systems with close, tidally locked brown dwarfs orbiting around white dwarfs belong to the post common envelope binaries or PCEBs. Only eight confirmed PCEBs containing a white dwarf with a brown dwarf companion are known, including WD 0137-349 AB. In the past history of these close white dwarf-brown dwarf binaries, the brown dwarf is engulfed by the star in the red giant phase. Brown dwarfs with a mass lower than 20 Jupiter masses would evaporate during the engulfment.[143][144] The dearth of brown dwarfs orbiting close to white dwarfs can be compared with similar observations of brown dwarfs around main-sequence stars, described as the brown-dwarf desert.[145][146] The PCEB might evolve into a cataclysmic variable star (CV*) with the brown dwarf as the donor.[147] Simulations have shown that highly evolved CV* are mostly associated with substellar donors (up to 80%).[148] A type of CV*, called WZ Sge-type dwarf nova often show donors with a mass near the borderline of low-mass stars and brown dwarfs.[149] The binary BW Sculptoris is such a dwarf nova with a brown dwarf donor. This brown dwarf likely formed when a donor star lost enough mass to become a brown dwarf. The mass loss comes with a loss of the orbital period until it reaches a minimum of 70–80 minutes at which the period increases again. This gives this evolutionary stage the name period bouncer.[148] There could also exist brown dwarfs that merged with white dwarfs. The nova CK Vulpeculae might be a result of such a white dwarf–brown dwarf merger.[150][151]
Brown dwarfs around neutron stars
Substellar objects around neutron stars are known. An example are black widow pulsars, which are named after the original black widow pulsar PSR B1957+20. About 41 such black widows are known. A black widow pulsar is characterized by a millisecond pulsar with a substellar companion that is ablated by the strong stellar wind of the pulsar. If the companion has a mass below 0.1 M☉, it is called black widow, above this mass it is called redback pulsar.[152]
Formation and evolution
Brown dwarfs form similarly to stars and are surrounded by protoplanetary disks,[153] such as Cha 110913−773444. As of 2017 there is only one known proto-brown dwarf that is connected with a large Herbig–Haro object. This is the brown dwarf Mayrit 1701117, which is surrounded by a pseudo-disk and a Keplerian disk.[154] Mayrit 1701117 launches the 0.7-light-year-long jet HH 1165, mostly seen in ionized sulfur.[155][156]
In 2020, the closest brown dwarf with an associated primordial disk—
A paper from 2021 studied circumstellar discs around brown dwarfs in stellar associations that are a few million years old and 140 to 200 parsecs away. The researchers found that these disks are not massive enough to form planets in the future. There is evidence in these disks that might indicate that planet formation begins at earlier stages and that planets are already present in these disks. The evidence for disk evolution includes a decreasing disk mass over time, dust grain growth and dust settling.[161] Disks around brown dwarfs usually have a radius smaller than 40 astronomical units, but three disks in the more distant Taurus molecular cloud have a radius larger than 70 au and were resolved with ALMA. These larger disks are able to form rocky planets with a mass >1 ME.[162] There are also brown dwarfs with disks in associations older than a few million years,[163] which might be evidence that disks around brown dwarfs need more time to dissipate. Especially old disks (>20 Myrs) are sometimes called Peter Pan disks. Currently 2MASS J02265658-5327032 is the only known brown dwarf that has a Peter Pan disk.[164]
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 MJ), and if it formed a planetary system, it would be the smallest-known object to have one.[165]
Planets around brown dwarfs
According to the IAU working definition (from August 2018) an exoplanet can orbit a brown dwarf. It requires a mass below 13 MJ and a mass ratio of M/Mcentral<2/(25+√621). This means that an object with a mass up to 3.2 MJ around a brown dwarf with a mass of 80 MJ is considered a planet. It also means that an object with a mass up to 0.52 MJ around a brown dwarf with a mass of 13 MJ is considered a planet.[167]
The
Planets around brown dwarfs are likely to be carbon planets depleted of water.[171]
A 2017 study, based upon observations with Spitzer estimates that 175 brown dwarfs need to be monitored in order to guarantee (95%) at least one detection of a below earth-sized planet via the transiting method.[172] JWST could potentially detect smaller planets. The orbits of planets and moons in the solar system often align with the orientation of the host star/planet they orbit. Assuming the orbit of a planet is aligned with the rotational axis of a brown dwarf or planetary-mass object, the geometric transit probability of an object similar to Io can be calculated with the formula cos(79.5°)/cos(inclination).[173] The inclination was estimated for several brown dwarfs and planetary-mass objects. SIMP 0136 for example has an estimated inclination of 80°±12.[174] Assuming the lower bound of i≥68° for SIMP 0136, this results in a transit probability of ≥48.6% for close-in planets. It is however not known how common close-in planets are around brown dwarfs and they might be more common for lower-mass objects, as disk sizes seem to decrease with mass.[161]
Habitability
Habitability for hypothetical planets
Superlative brown dwarfs
In 1984, it was postulated by some astronomers that the Sun may be orbited by an undetected brown dwarf (sometimes referred to as
Table of firsts
Record | 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 | 2M1207 | M8 | 12h07m33.47s −39°32'54.0" | Centaurus | Planet discovered in 2004 |
First with a circumstellar disk | ChaHα1 | M7.5 | 11h07m17.0s -77°35'54" | Chamaeleon | Disk discovered in 2000, first disk around a bona fide brown dwarf, also first x-ray emitting[177] |
First with bipolar outflow | Rho-Oph 102 (SIMBAD: [GY92] 102) | 16 26 42.758 -24 41 22.24 | Ophiuchus | partly resolved outflow[178] | |
First with large-scale Herbig-Haro object | Mayrit 1701117
(Herbig-Haro object: HH 1165) |
proto-BD | 05 40 25.799 -02 48 55.42 | Orion | projected length of the Herbig-Haro object: 0.8 light-years (0.26 pc)[156] |
First field type (solitary) | Teide 1 | M8 | 3h47m18.0s +24°22'31" | Taurus | 1995 |
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[179] | M6.5 | 03h 48m 4.659s +23° 39' 30.32″ | Taurus | Basri and Martín 1999 |
First eclipsing binary brown dwarf | M6.5 | Orion | Stassun 2006, 2007 (distance ~450 pc) | ||
First binary brown dwarf of T Type | Epsilon Indi Ba, Bb[180] | T1 + T6 | 22h 03m 21.65363s −56° 47′ 09.5228″ | Indus | Distance: 3.626pc |
First binary brown dwarf of Y Type | WISE J0336−0143 | Y+Y | 03h 36m 05.052s −01° 43′ 50.48″ | Eridanus | 2023[93] |
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[181] |
First halo brown dwarf | 2MASS J05325346+8246465 | sdL7 | 05h32m53.46s +82°46'46.5" | Gemini | Burgasser et al. 2003[182] |
First with late-M spectrum | Teide 1 | M8 | 3h47m18.0s +24°22'31" | Taurus | 1995 |
First with L spectrum | GD 165B | L4 | 14h 24m 39.144s 09° 17′ 13.98″ | Boötes | 1988 |
First with T spectrum | Gliese 229 B | T6.5 | 06h10m34.62s −21°51'52.1" | Lepus | 1995 |
Latest-T spectrum | ULAS J003402.77−005206.7 | T9[64] | Cetus | 2007 | |
First with Y spectrum | CFBDS0059[63] | ~Y0 | 00h 59m 10.83s −01° 14′ 01.3″ | Cetus | 2008; this is also classified as a T9 dwarf, due to its close resemblance to other T dwarfs.[64] |
First X-ray-emitting | ChaHα1 | 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[112] |
First potential brown dwarf auroras discovered | LSR J1835+3259 | M8.5 | Lyra | 2015 | |
First detection of differential rotation in a brown dwarf | TVLM 513-46546 | M9 | 15h01m08.3s +22°50'02" | Boötes | Equator rotates faster than poles by 0.022 radians / day[183] |
First confirmed brown dwarf to have survived the primary's red giant phase | WD 0137−349 B[184] | L8 | 01h 39m 42.847s −34° 42′ 39.32″ | Sculptor (constellation) |
Table of extremes
Record | Name | Spectral type | RA/Dec | Constellation | Notes |
---|---|---|---|---|---|
Oldest |
T8 sdT8 L8 |
00h 55m 58.300s +59° 48′ 02.53″ or 20h 05m 02.1951s +54° 26′ 03.234″ or 06h 02m 02.17s −46° 24′ 47.8″ |
Cassiopeia, Cygnus or Pictor | three of the few examples with a good age estimate:
LSPM J0055B: 10±3 Wolf 1130C: >10 billion years[185] CWISE J0602-4624: 10.9+2.6 | |
Youngest | 2MASS J05413280-0151272 | M8.5 | 05h 41m 32.801s −01° 51′ 27.20″ | Orion | One brown dwarf member of the about 0.5 Myr-old Flame Nebula. 20.9 MJ object[187] |
Most massive | SDSS J010448.46+153501.8[188] | usdL1.5 | 01h04m48.46s +15°35'01.8" | Pisces | distance is ~180–290 pc, mass is ~88.5–91.7 MJ. Transitional brown dwarfs. |
Metal-rich | |||||
Metal-poor | SDSS J010448.46+153501.8[188] | usdL1.5 | 01h04m48.46s +15°35'01.8" | Pisces | distance is ~180–290 pc, metallicity is ~0.004 ZSol. Transitional brown dwarfs. |
Least massive | OTS 44 | M9.5 | 11h 10m 11.5s −76° 32′ 13″ | Chamaeleon | Has a mass range of 11.5–15 MJ, distance is ~550 ly |
Largest | |||||
Smallest | WISEA 1810−1010 | esdT | 18h 10m 06.18s−10° 10′ 00.5″ | Serpens | Radius is 0.65+0.31 −0.19 RJ (~92,400 km)[189] |
Fastest rotating | 2MASS J03480772−6022270 | T7 | 03h48m07.72s –60°22'27.1" | Reticulum | Rotational period of 1.080+0.004 −0.005 hours[190] |
Farthest | KMT-2016-BLG-2142 b | 17h 52m 27.0s –29° 23′ 04″ | Sagittarius | (microlensing)[191] has a distance of 5,850 to 8,020 parsec. Could also be massive gas giant.[192] | |
Nearest | Luhman 16 AB | L7.5 + T0.5 ± 1 | 10h 49m 18.723s −53° 19′ 09.86″ | Vela | Distance: ~6.5 ly |
Brightest | LP 944-20 | opt: M9beta,
IR: L0: |
03h 39m 35.220s −35° 25′ 44.09″ | Fornax | According to the ultracool fundamental properties[193] this object shows signs of youth and could therefore be a brown dwarf with 19.85±13.02 MJ and JMKO=10.68±0.03 mag |
Dimmest | L 97-3B
|
Y1 | 08h 06m 53.736s −66° 18′ 16.74″ | Volans | jmag=25.42, planetary-mass object |
Hottest | |||||
Coolest | WISE 0855−0714[79] | Y4 | 08h 55m 10.83s −07° 14′ 42.5″ | Hydra | Temperature: −48 to −13 °C (225 to 260 K; −54 to 9 °F) |
Coolest radio-flaring | WISE J062309.94-045624.6 | T8 | 06h23m09.28s −04°56'22.8" | Monoceros
|
699 K (426 °C; 799 °F) brown dwarf with 4.17 mJy bursts[194] |
Most dense | TOI-569b[195] | 07h 40m 24.658s -42° 09′ 16.74″ | Puppis | Transiting, has 64.1 MJ with a diameter 0.79 ± 0.02 times that of Jupiter. Density is 171.3g/cm3.
| |
Least dense |
Gallery
-
Brown dwarf illustration[196]
See also
- Fusor (astronomy)
- Brown-dwarf desert – Theorized range of orbits around a star within which brown dwarfs cannot exist as companion objects
- Blue dwarf (red-dwarf stage) – Hypothetical class of star that develops from a red dwarf
- Dark matter – Concept in cosmology
- Exoplanet – Planet outside the Solar System
- Stellification
- WD 0032-317 b
- List of brown dwarfs
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We find that the brown dwarf radius ranges between 0.64–1.13 RJ with an average radius of 0.83 RJ.
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- ISSN 0004-637X.
- ISSN 0004-637X.
- ^
Barnes, Rory; Heller, René (2011). "Habitable Planets Around White and Brown Dwarfs: The Perils of a Cooling Primary". Astrobiology. 13 (3): 279–291. PMID 23537137.
- ^ Morrison, David (2 August 2011). "Scientists today no longer think an object like Nemesis could exist". NASA Ask An Astrobiologist. Archived from the original on 13 December 2012. Retrieved 2011-10-22.
- ISSN 0004-6361.
- S2CID 4415442.
- S2CID 17662168.
- ^ Scholz, Ralf-Dieter; McCaughrean, Mark (2003-01-13). "eso0303 – Discovery of Nearest Known Brown Dwarf" (Press release). European Southern Observatory. Archived from the original on October 13, 2008. Retrieved 2013-03-16.
- S2CID 119336794.
- S2CID 11895472.
- S2CID 119114679.
- S2CID 4368344. Archived from the originalon 2021-04-27.
- S2CID 56431008.
- .
- S2CID 118955538.
Table 3: FLMN_J0541328-0151271
- ^ S2CID 54847595.
- .
- S2CID 232105126.
- ^ "The Extrasolar Planet Encyclopaedia — KMT-2016-BLG-2142 b". Extrasolar Planets Encyclopaedia. Retrieved 2021-01-12.
- ISSN 0004-6256.
- .
- S2CID 259262475.
- ^ Astrobites (24 June 2020). "Transiting Brown Dwarfs from TESS 2". AAS Nova. Retrieved 2013-03-16.
- ^ Tannock, Megan; Metchev, Stanimir; Kocz, Amanda (7 April 2021). "Caught Speeding: Clocking the Fastest-Spinning Brown Dwarfs". NOIRLab. Retrieved 9 April 2021.
External links
- HubbleSite newscenter – Weather patterns on a brown dwarf
- Allard, France; Homeier, Derek (2007). "Brown dwarfs". .
History
- Kumar, Shiv S.; Low-Luminosity Stars. Gordon and Breach, London, 1969—an early overview paper on brown dwarfs
- The Columbia Encyclopedia: "Brown Dwarfs"
Details
- A current list of L and T dwarfs
- A geological definition of brown dwarfs, contrasted with stars and planets (via Berkeley)
- I. Neill Reid's pages at the Space Telescope Science Institute:
- On spectral analysis of T dwarfs
- Temperature and mass characteristics of low-temperature dwarfs
- On spectral analysis of
- First X-ray from brown dwarf observed, Spaceref.com, 2000
- Montes, David; "Brown Dwarfs and ultracool dwarfs (late-M, L, T)", UCM
- Wild Weather: Iron Rain on Failed Stars—scientists are investigating astonishing weather patterns on brown dwarfs, Space.com, 2006
- NASA Brown dwarf detectives Archived 2014-10-17 at the Wayback Machine—Detailed information in a simplified sense
- Brown Dwarfs—Website with general information about brown dwarfs (has many detailed and colorful artist's impressions)
Stars
- Cha Halpha 1 stats and history
- "A census of observed brown dwarfs" (not all confirmed), 1998
- Luhman, Kevin L.; Adame, Lucía; d'Alessio, Paola; Calvet, Nuria; Hartmann, Lee; Megeath, S. Thomas; Fazio, Giovanni G. (2005). "Discovery of a Planetary-Mass Brown Dwarf with a Circumstellar Disk". The Astrophysical Journal. 635 (1): L93–L96. S2CID 11685964.
- Michaud, Peter; Heyer, Inge; Leggett, Sandy K.; and Adamson, Andy; "Discovery Narrows the Gap Between Planets and Brown Dwarfs", Gemini and Joint Astronomy Centre, 2007
- Deacon, Niall R.; and Hambly, Nigel C.; "Y-Spectral class for Ultra-Cool Dwarfs", 2006