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Brown dwarf

Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main-sequence stars. Their mass is approximately 13 to 80 times that of Jupiter   —not big enough to sustain nuclear fusion of ordinary hydrogen (1H) into helium in their cores, but massive enough to emit some light and heat from the fusion of deuterium (2H). The most massive ones (> ) can fuse lithium (7Li).

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. 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 white dwarf stars and "dark" planets in size. To the naked eye, brown dwarfs would appear in different colors depending on their temperature. The warmest ones are possibly orange or red, while cooler brown dwarfs would likely appear magenta or black to the human eye. Brown dwarfs may be fully convective, with no layers or chemical differentiation by depth.

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 ly from the Sun. Luhman 16 is the third closest system to the Sun after Alpha Centauri and Barnard's Star.

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, 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.

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.

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. The first self-consistent calculation of the hydrogen-burning minimum mass confirmed a value between 0.07 and 0.08 solar masses for population I objects.

Deuterium fusion
The discovery of deuterium burning down to ($13.6 MJ$) 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 these objects. These methods included multi-color imaging surveys around field stars, imaging surveys for faint companions of main-sequence dwarfs and white dwarfs, surveys of young star clusters, and radial velocity monitoring for close companions.

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".

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.

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. Hence, the detection of lithium in the atmosphere of an object older than 100 Myr ensures that it is a brown dwarf.

Gliese 229B and class T
The first class "T" brown dwarf was discovered in 1994 by Caltech astronomers Shrinivas Kulkarni, Tadashi Nakajima, Keith Matthews and Rebecca Oppenheimer, and Johns Hopkins scientists Samuel T. Durrance and David Golimowski. It was confirmed in 1995 as a substellar companion to Gliese 229. Gliese 229b is one of the first two instances of clear evidence for a brown dwarf, along with Teide 1. Confirmed in 1995, both were identified by the presence of the 670.8 nm lithium line. The latter was found to have a temperature and luminosity well below the stellar range.

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 Rafael Rebolo (head of the team), María Rosa Zapatero-Osorio, and Eduardo L. Martín in 1994. This object, found in the Pleiades open cluster, received the name Teide 1. The discovery article was submitted to Nature in May 1995, and published on 14 September 1995. Nature highlighted "Brown dwarfs discovered, official" on the front page of that issue.

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, 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 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, 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.

Theory
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 due to the Kelvin–Helmholtz mechanism. 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 increase 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 a typical star, gas and radiation pressure generated by the thermonuclear fusion reactions within its core 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.

If, however, the initial mass of the protostar is less than about, normal hydrogen thermonuclear fusion reactions will not ignite in the core. Gravitational contraction does not heat the small protostar very effectively, and before the temperature in the core can increase enough to trigger fusion, the density reaches the point where electrons become closely packed enough to create quantum electron degeneracy pressure. According to the brown dwarf interior models, typical conditions in the core for density, temperature and pressure are expected to be the following:
 * $$10\,\mathrm{g/cm^3} \,\lesssim\, \rho_c \,\lesssim\, 10^3\,\mathrm{{g}/{cm^{3}}} $$
 * $$T_c \lesssim 3 \times 10^6\,\mathrm{K} $$
 * $$P_c \sim 10^5\,\mathrm{Mbar}.$$

This means that the protostar is not massive 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 hydrogen burning limit without initiating hydrogen fusion. This could happen via mass transfer in a binary brown dwarf system.

High-mass brown dwarfs versus low-mass stars
Lithium is generally present in brown dwarfs and not in low-mass stars. Stars, which reach the high temperature necessary for fusing hydrogen, rapidly deplete their lithium. Fusion of lithium-7 and a proton occurs, producing two helium-4 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 can burn their lithium by the time they are half a billion years old; 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 bolometric luminosity that they can sustain through steady fusion. This luminosity varies from star to star, but is generally at least 0.01% that of the Sun. Brown dwarfs cool and darken steadily over their lifetimes; sufficiently old brown dwarfs will be too faint to be detectable. 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. Young L/T-dwarfs (L2-T4) show high variability, which could be explained with clouds, hot spots, magnetically driven aurorae or thermochemical instabilities. 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. It is however not clear if silicate clouds are always necessary for young objects. 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. Additionally, MIRI has observed silicate absorption in the planetary-mass companion VHS 1256b.

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.

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. 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.

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.

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, the volume of a brown dwarf is governed primarily by electron-degeneracy pressure, as it is in white dwarfs; at the low end of the range , 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 ($0.08 M_Solar$), suggesting that from this perspective brown dwarfs are simply high-mass Jovian planets. 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 ) cool quickly enough that after 10 million years they no longer undergo fusion.

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. 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 (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 ) forms the upper limit of the definition.

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. Under this interpretation brown dwarfs are those objects that represent the lowest-mass products of the star formation process, while planets are objects formed in an accretion disk surrounding a star. The coolest free-floating objects discovered, such as WISE 0855, as well as the lowest-mass young objects known, like PSO J318.5−22, are thought to have masses below, and as a result are sometimes referred to as planetary-mass objects due to the ambiguity of whether they should be regarded as rogue planets or brown dwarfs. There are planetary-mass objects known to orbit brown dwarfs, such as 2M1207b, MOA-2007-BLG-192Lb, 2MASS J044144b and Oph 98 B.

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. 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.

As of 2011 the Extrasolar Planets Encyclopaedia included objects up to 25 Jupiter masses, saying, "The fact that there is no special feature around in the observed mass spectrum reinforces the choice to forget this mass limit". As of 2016, this limit was increased to 60 Jupiter masses, based on a study of mass–density relationships.

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." The NASA Exoplanet Archive includes objects with a mass (or minimum mass) equal to or less than 30 Jupiter masses.

Sub-brown dwarf

Objects below, 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.

Some researchers call them free-floating planets, whereas others call them planetary-mass brown dwarfs.

Role of other physical properties in the mass estimate
While spectroscopic features can help to distinguish between low-mass stars and brown dwarfs, it is often necessary to estimate the mass to come to a conclusion. The theory behind the mass estimate is that brown dwarfs with a similar mass form in a similar way and are hot when they form. Some have spectral types that are similar to low-mass stars, such as 2M1101AB. As they cool down the brown dwarfs should retain a range of luminosities depending on the mass. Without the age and luminosity, a mass estimate is difficult; for example, an L-type brown dwarf could be an old brown dwarf with a high mass (possibly a low-mass star) or a young brown dwarf with a very low mass. For Y dwarfs this is less of a problem, as they remain low-mass objects near the sub-brown dwarf limit, even for relatively high age estimates. For L and T dwarfs it is still useful to have an accurate age estimate. The luminosity is here the less concerning property, as this can be estimated from the spectral energy distribution. The age estimate can be done in two ways. Either the brown dwarf is young and still has spectral features that are associated with youth, or the brown dwarf co-moves with a star or stellar group (star cluster or association), where age estimates are easier to obtain. A very young brown dwarf that was further studied with this method is 2M1207 and the companion 2M1207b. Based on the location, proper motion and spectral signature, this object was determined to belong to the ~8-million-year-old TW Hydrae association, and the mass of the secondary was determined to be 8 ± 2, below the deuterium burning limit. An example of a very old age obtained by the co-movement method is the brown dwarf + white dwarf binary COCONUTS-1, with the white dwarf estimated to be $7.3$ billion years old. In this case the mass was not estimated with the derived age, but the co-movement provided an accurate distance estimate, using Gaia parallax. Using this measurement the authors estimated the radius, which was then used to estimate the mass for the brown dwarf as $15.4$.

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. 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 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 objects like GD 165B ultimately led to the definition of a new spectral class, the L dwarfs, defined in the red optical region of the spectrum not by metal-oxide absorption bands (TiO, VO), but by metal hydride emission bands (FeH, CrH, MgH, CaH) and prominent atomic lines of alkali metals (Na, K, Rb, Cs). , over 900 L dwarfs had been identified, 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). This spectral class also contains the coolest main-sequence stars (> 80 MJ), which have spectral classes L2 to L6.

Spectral class T

As GD 165B is the prototype of the L dwarfs, Gliese 229B is the prototype of a second new spectral class, the T dwarfs. T dwarfs are pinkish-magenta. 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), a feature which in the Solar System is found only in the giant planets 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 J. Davy Kirkpatrick to propose the T spectral class for objects exhibiting H- and K-band CH4 absorption. , 355 T dwarfs were known. 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 magenta. T-class brown dwarfs, such as WISE 0316+4307, have been detected more than 100 light-years from the Sun.

Spectral class Y

In 2009, the coolest-known brown dwarfs had estimated effective temperatures between 500 and(-), 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. The spectra of these objects have absorption peaks around 1.55 micrometres. 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. However, the feature is difficult to distinguish from absorption by water and methane, and other authors have stated that the assignment of class Y0 is premature.

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.

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.

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.

 * 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 and mass of Jupiter mass. Though of planetary mass, Rodriguez et al. suggest it is unlikely to have formed in the same manner as planets.

 * February 2011: Shortly after that, Liu et al. published an account of a "very cold" (c. 370 K) 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."

 * 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. These were published in two papers.

 * July 2012: Seven new Y-dwarfs were discovered, making the total number of confirmed Y-dwarfs fourteen. 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. Its temperature has since been revised, and newer estimates put it in the range of 250 to 400 K.

 * November 2012: WISE J1639−6847 was discovered. As of February 2024 it was the second-closest known Y-dwarf to Earth.
 * April 2014: WISE 0855−0714 was announced, with a temperature profile estimated around 225 to(-) and a mass of . 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.
 * November 2014: The object WISEA J1141−3326 was estimated to be a Y-dwarf and it was later confirmed.
 * April 2015: The T+Y dwarf binary WISE J0146+4234 AB was discovered.
 * May 2015: Three Y-dwarfs were discovered with Hubble, bringing the total number of confirmed Y-dwarfs to 21.
 * June 2018: WISEA J0302−5817 was published as a Y-dwarf, and WISEA J1141−3326 was confirmed as a Y-dwarf.
 * 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(-). In 2023 it was announced that CWISEP J1935-1546 had methane emission due to an aurora.
 * 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.

 * February 2020: The CatWISE catalog combined NASA's WISE and NEOWISE surveys. 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. Additional data with Spitzer showed that CW1446 is the fifth-reddest brown dwarf, with a temperature of about 310 to(-) and a distance of about 10 parsecs.
 * August 2020: Five candidate Y-dwarfs were discovered via the Backyard Worlds project.
 * April 2021: New Y-dwarf candidates were published by the CatWISE and Backyard Worlds teams in a collaborative paper.
 * August 2021: Ross 19B, an old object near the T/Y-boundary orbiting an M-dwarf, was discovered by the Backyard Worlds team.
 * April 2023: WISE J0336−0143 was confirmed as a Y-dwarf binary with JWST. The B secondary is likely one of the coldest confirmed Y-dwarfs as of December 2023, with an estimated temperature of 246 to(-).
 * November 2023: CWISE J1055+5443, an object previously classified as a T-dwarf, was confirmed as a nearby Y-dwarf.
 * December 2023: Three new Y-dwarf candidates were published. 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).

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.

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. 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. 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.

Secondary features
Young brown dwarfs have low surface gravities because they have larger radii and lower masses than the field stars of similar spectral type. These sources are noted by a letter beta (β) for intermediate surface gravity or gamma (γ) for low surface gravity. Indicators of low surface gravity include weak CaH, K I and Na I lines, as well as a strong VO line. Alpha (α) denotes normal surface gravity and is usually dropped. Sometimes an extremely low surface gravity is denoted by a delta (δ). The suffix "pec" stands for "peculiar"; this suffix is still used for other features that are unusual, and summarizes different properties, indicating low surface gravity, subdwarfs and unresolved binaries. The prefix sd stands for subdwarf and only includes cool subdwarfs. This prefix indicates a low metallicity and kinematic properties that are more similar to halo stars than to disk stars. Subdwarfs appear bluer than disk objects. The red suffix describes objects with red color, but an older age. This is not interpreted as low surface gravity, but as a high dust content. The blue suffix describes objects with blue near-infrared colors that cannot be explained with low metallicity. Some are explained as L+T binaries, others are not binaries, such as 2MASS J11263991−5003550 and are explained with thin and/or large-grained clouds.

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 $750 K$. 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).

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.

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.

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. 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 Gliese 229A (20 ly away) using an adaptive optics coronagraph to sharpen images from the 60 in reflecting telescope at Palomar Observatory on Southern California's Mount Palomar; follow-up infrared spectroscopy made with their 200 in Hale Telescope shows 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 (, 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 detected emission from LP 944–20.
 * 30 April 2004: First detection of a candidate exoplanet around a brown dwarf: 2M1207b discovered with the VLT and the first directly imaged exoplanet.
 * 20 March 2013: Discovery of the closest brown dwarf system: Luhman 16.
 * 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.

Brown dwarf as an X-ray source

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, 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. 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. "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. "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. "This observation, thus, raises the possibility that even massive planets might emit X-rays by themselves during their youth!"

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. The power of the radio emissions of brown dwarfs is roughly constant despite variations in their temperatures. Brown dwarfs may maintain magnetic fields of up to 6 kG in strength. Astronomers have estimated brown dwarf magnetospheres to span an altitude of approximately 107 m given properties of their radio emissions. 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.

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. 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. (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).

In August 2020, astronomers discovered 95 brown dwarfs near the Sun through the project Backyard Worlds: Planet 9.

Brown dwarf-Brown dwarf binaries
Brown dwarfs binaries of type M, L, and T are less common with a lower mass of the primary. L-dwarfs have a binary fraction of about $24$% and the binary fraction for late T, early Y-dwarfs (T5-Y0) is about 8±6%.

Brown dwarf binaries have a higher companion-to-host ratio $$q=M_B/M_A$$ 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.

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. 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.

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. 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.

Unusual brown dwarf binaries
The wide binary system 2M1101AB was the first binary with a separation greater than $20 AU$. The discovery of the system gave definitive insights to the formation of brown dwarfs. It was previously thought that wide binary brown dwarfs are not formed or at least are disrupted at ages of 1–10 Myr. The existence of this system is also inconsistent with the ejection hypothesis. The ejection hypothesis was a proposed hypothesis in which brown dwarfs form in a multiple system, but are ejected before they gain enough mass to burn hydrogen.

More recently the wide binary W2150AB was discovered. It has a similar mass ratio and binding energy as 2M1101AB, but a greater age and is located in a different region of the galaxy. While 2M1101AB is in a closely crowded region, the binary W2150AB is in a sparsely-separated field. It must have survived any dynamical interactions in its natal star cluster. The binary belongs also to a few L+T binaries that can be easily resolved by ground-based observatories. The other two are SDSS J1416+13AB and Luhman 16.

There are other interesting binary systems such as the eclipsing binary brown dwarf system 2MASS J05352184–0546085. Photometric studies of this system have revealed that the less massive brown dwarf in the system is hotter than its higher-mass companion.

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.

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.

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). The Working Group on Extrasolar Planets (WGESP) of the IAU on the other hand only considers planets with a mass below 13 Jupiter masses.

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. 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), and LSPM J0055+5948 AB (10 billion years old), SDSS J22255+0016 AB (2 billion years old) WD 0806−661 AB (1.5–2.7 billion years old).

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. 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. The PCEB might evolve into a cataclysmic variable star (CV*) with the brown dwarf as the donor. Simulations have shown that highly evolved CV* are mostly associated with substellar donors (up to 80%). 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. 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. 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.

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, it is called black widow, above this mass it is called redback pulsar.

Formation and evolution
Brown dwarfs form similarly to stars and are surrounded by protoplanetary disks, 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. Mayrit 1701117 launches the 0.7-light-year-long jet HH 1165, mostly seen in ionized sulfur.

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. Given the small mass of brown dwarf disks, most planets will be terrestrial planets rather than gas giants. 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. 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.

In 2020, the closest brown dwarf with an associated primordial disk—WISEA J120037.79-784508.3 (W1200-7845)—was discovered by the Disk Detective project when classification volunteers noted its infrared excess. It was vetted and analyzed by the science team who found that W1200-7845 had a 99.8% probability of being a member of the ε Chamaeleontis (ε Cha) young moving group association. Its parallax (using Gaia DR2 data) puts it at a distance of 102 parsecs (or 333 lightyears) from Earth—which is within the local Solar neighborhood.

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. 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. There are also brown dwarfs with disks in associations older than a few million years, 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.

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, and if it formed a planetary system, it would be the smallest-known object to have one.

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 and a mass ratio of M/Mcentral<2/(25+√621). This means that an object with a mass up to 3.2 around a brown dwarf with a mass of 80  is considered a planet. It also means that an object with a mass up to 0.52 around a brown dwarf with a mass of 13  is considered a planet.

The super-Jupiter planetary-mass objects 2M1207b, 2MASS J044144 and Oph 98 B that are orbiting brown dwarfs at large orbital distances 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. The first discovery of a low-mass companion orbiting a brown dwarf (ChaHα8) at a small orbital distance using the radial velocity technique paved the way for the detection of planets around brown dwarfs on orbits of a few AU or smaller. However, with a mass ratio between the companion and primary in ChaHα8 of about 0.3, this system rather resembles a binary star. Then, in 2008, the first planetary-mass companion in a relatively small orbit (MOA-2007-BLG-192Lb) was discovered orbiting a brown dwarf.

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

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. 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). The inclination was estimated for several brown dwarfs and planetary-mass objects. SIMP 0136 for example has an estimated inclination of 80°±12. 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.

Habitability
Habitability for hypothetical planets orbiting brown dwarfs has been studied. Computer models suggesting conditions for these bodies to have habitable planets are very stringent, the habitable zone being narrow, close (T dwarf 0.005 AU) and decreasing with time, due to the cooling of the brown dwarf (they fuse for at most 10 million years). The orbits there would have to be of extremely low eccentricity (on the order of 10 to the minus 6) to avoid strong tidal forces that would trigger a runaway greenhouse effect on the planets, rendering them uninhabitable. There would also be no moons.

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 Nemesis) that could interact with the Oort cloud just as passing stars can. However, this hypothesis has fallen out of favor.

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 M dwarfs, L dwarfs, and T dwarfs
 * Temperature and mass characteristics of low-temperature dwarfs
 * 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 —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
 * 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
 * Deacon, Niall R.; and Hambly, Nigel C.; "Y-Spectral class for Ultra-Cool Dwarfs", 2006

title: Brown dwarf


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Shakers

The United Society of Believers in Christ's Second Appearing, more commonly known as the Shakers, are a millenarian restorationist Christian sect founded c. 1747 in England and then organized in the United States in the 1780s. They were initially known as "Shaking Quakers" because of their ecstatic behavior during worship services.

Espousing egalitarian ideals, women took on spiritual leadership roles alongside men, including founding leaders such as Jane Wardley, Ann Lee, and Lucy Wright. The Shakers emigrated from England and settled in Revolutionary colonial America, with an initial settlement at Watervliet, New York (present-day Colonie), in 1774. They practice a celibate and communal utopian lifestyle, pacifism, uniform charismatic worship, and their model of equality of the sexes, which they institutionalized in their society in the 1780s. They are also known for their simple living, architecture, technological innovation, music, and furniture.

During the mid-19th century, an Era of Manifestations resulted in a period of dances, gift drawings, and gift songs inspired by spiritual revelations. At its peak in the mid-19th century, there were 2,000–4,000 Shaker believers living in 18 major communities and numerous smaller, often short-lived communities. External and internal societal changes in the mid- and late-19th century resulted in the thinning of the Shaker community as members left or died with few converts to the faith to replace them.

By 1920, there were only 12 Shaker communities remaining in the United States. , there is only one active Shaker village: Sabbathday Lake Shaker Village, in Maine. Consequently, many of the other Shaker settlements are now museums.

Origins
The Shakers were one of a few religious groups which were formed during the 18th century in the northwest of England; originating out of the Wardley Society. James and Jane Wardley and others broke off from the Quakers in 1747  at a time when the Quakers were weaning themselves away from frenetic spiritual expression. The Wardleys formed the Wardley Society, which was also known as the "Shaking Quakers".

Future leader Ann Lee and her parents were early members of the sect. This group of "charismatic" Christians became the United Society of Believers in Christ's Second Appearing (USBCSA). Their beliefs were based upon spiritualism and included the notion that they received messages from the Holy Spirit which were expressed during religious revivals. They also experienced what they interpreted as messages from God during silent meditations and became known as "Shaking Quakers" because of the ecstatic nature of their worship services. They believed in the renunciation of sinful acts and that the end of the world was near.

Meetings were first held in Bolton, England, where the articulate preacher, Jane Wardley, urged her followers to:

"Repent. For the kingdom of God is at hand. The new heaven and new earth prophesied of old is about to come. The marriage of the Lamb, the first resurrection, the new Jerusalem descended from above, these are even now at the door. And when Christ appears again, and the true church rises in full and transcendent glory, then all anti-Christian denominations—the priests, the Church, the pope—will be swept away."

Other meetings were then held in Manchester, Meretown (also spelled Mayortown), Chester and other places near Manchester. As their numbers grew, members began to be persecuted, mobbed, and stoned; Lee was imprisoned in Manchester. The members looked to women for leadership, believing that the second coming of Christ would be through a woman. In 1770, Ann Lee was revealed in "manifestation of Divine light" to be the second coming of Christ and was called Mother Ann.

Mother Ann Lee
Ann Lee joined the Shakers by 1758, then became the leader of the small community. "Mother Ann", as her followers later called her, claimed numerous revelations regarding the fall of Adam and Eve and its relationship to sexual intercourse. A powerful preacher, she called her followers to confess their sins, give up all their worldly goods, and take up the cross of celibacy and forsake marriage, as part of the renunciation of all "lustful gratifications".

She said:

"I saw in vision the Lord Jesus in his kingdom and glory. He revealed to me the depth of man's loss, what it was, and the way of redemption therefrom. Then I was able to bear an open testimony against the sin that is the root of all evil; and I felt the power of God flow into my soul like a fountain of living water. From that day I have been able to take up a full cross against all the doleful works of the flesh."

Having supposedly received a revelation, on May 19, 1774, Ann Lee and eight of her followers sailed from Liverpool for colonial America. Ann and her husband Abraham Stanley, brother William Lee, niece Nancy Lee, James Whittaker, father and son John Hocknell and Richard Hocknell, James Shephard, and Mary Partington traveled to colonial America and landed in New York City. Abraham Stanley abandoned Ann Lee shortly thereafter and remarried. The remaining Shakers settled in Watervliet, New York, in 1776. Mother Ann's hope for the Shakers in America was represented in a vision: "I saw a large tree, every leaf of which shone with such brightness as made it appear like a burning torch, representing the Church of Christ, which will yet be established in this land." Unable to swear an Oath of Allegiance, as it was against their faith, the members were imprisoned for about six months. Since they were only imprisoned because of their faith, this raised sympathy of citizens and thus helped to spread their religious beliefs. Mother Ann, revealed as the "second coming" of Christ, traveled throughout the eastern states, preaching her gospel views.

Joseph Meacham and communalism

After Ann Lee and James Whittaker died, Joseph Meacham (1742–1796) became the leader of the Shakers in 1787, establishing its New Lebanon headquarters. He had been a New Light Baptist minister in Enfield, Connecticut, and was reputed to have, second only to Mother Ann, the spiritual gift of revelation.

Joseph Meacham brought Lucy Wright (1760–1821) into the Ministry to serve with him and together they developed the Shaker form of communal living (religious communism). By 1793 property had been made a "consecrated whole" in each Shaker community.

Shakers developed written covenants in the 1790s. Those who signed the covenant had to confess their sins, consecrate their property and their labor to the society, and live as celibates. If they were married before joining the society, their marriages ended when they joined. A few less-committed Believers lived in "noncommunal orders" as Shaker sympathizers who preferred to remain with their families. The Shakers never forbade marriage for such individuals, but considered it less perfect than the celibate state.

In the 5 years between 1787 and 1792, the Shakers gathered into eight more communities in addition to the Watervliet and New Lebanon villages: Hancock, Harvard, Shirley, and Tyringham Shaker Villages in Massachusetts; Enfield Shaker Village in Connecticut; Canterbury and Enfield in New Hampshire; and Sabbathday Lake and Alfred Shaker Village in Maine.

Lucy Wright and westward expansion
After Joseph Meacham died, Lucy Wright continued Ann Lee's missionary tradition. Shaker missionaries proselytized at revivals, not only in New England and New York but also farther west. Missionaries such as Issachar Bates and Benjamin Seth Youngs (older brother of Isaac Newton Youngs) gathered hundreds of proselytes into the faith.

On April 12, of 1805 Benjamin Youngs, and two companions, held the first ceremony west of the Allegheny Mountains. It was held at the cabin of James Beedle, East of Lebanon, Ohio. In 2019, the cabin was relocated, by the Warren County Historical Society, to its current site next to Harmon Museum in Lebanon, Ohio.

Mother Lucy Wright introduced new hymns and dances to make sermons more lively. She also helped write Benjamin S. Youngs' book The Testimony of Christ's Second Appearing (1808).

Shaker missionaries entered Kentucky and Ohio after the Cane Ridge, Kentucky revival of 1801–1803, which was an outgrowth of the Logan County, Kentucky, Revival of 1800. From 1805 to 1807, they founded Shaker societies at Union Village, Ohio; South Union, Logan County, Kentucky; and Pleasant Hill, Kentucky (in Mercer County, Kentucky). In 1806, a Shaker village, named Watervliet, after the New York town that was the site of the first Shaker settlement, was established in what is today Kettering, Ohio, surviving until 1900 when its remaining adherents joined the Union Village Shaker settlement. In 1824, the Whitewater Shaker Settlement was established in southwestern Ohio. The westernmost Shaker community was located at West Union (called Busro because it was on Busseron Creek) on the Wabash River a few miles north of Vincennes in Knox County, Indiana.

Era of Manifestations
The Shaker movement was at its height between 1820 and 1860. It was at this time that the sect had the most members, and the period was considered its "golden age". It had expanded from New England to the Midwestern states of Indiana and Ohio and Southern state of Kentucky. It was during this period that it became known for its furniture design and craftsmanship. In the late 1830s a spiritual revivalism, the Era of Manifestations was born. It was also known as the "period of Mother's work", for the spiritual revelations that were passed from the late Mother Ann Lee.

The expression of "spirit gifts" or messages were realized in "gift drawings" made by Hannah Cohoon, Polly Reed, Polly Collins, and other Shaker sisters. A number of those drawings remain as important artifacts of Shaker folk art.

Isaac N. Youngs, the scribe and historian for the New Lebanon, New York, Church Family of Shakers, preserved a great deal of information on the era of manifestations, which Shakers referred to as Mother Ann's Work, in his Domestic Journal, his diary, Sketches of Visions, and his history, A Concise View of the Church of God.

In addition, Shakers preserved thousands of spirit communications still extant in collections now held by the Berkshire Athenaeum, Fruitlands Museums Library, Hamilton College Library, Hancock Shaker Village, Library of Congress, New York Public Library, New York State Library, the Shaker Library at Sabbathday Lake Shaker Village, Shaker Museum | Mount Lebanon, Western Reserve Historical Society, Williams College Archives, Winterthur Museum Library, and other repositories.

American Civil War period
As pacifists, the Shakers did not believe that it was acceptable to kill or harm others, even in time of war. During the American Civil War, both Union and Confederate soldiers found their way to the Shaker communities. Shakers tended to sympathize with the Union but they did feed and care for both Union and Confederate soldiers. President Lincoln exempted Shaker males from military service, and they became some of the first conscientious objectors in American history.

The end of the Civil War brought large changes to the Shaker communities. One of the most important changes was the postwar economy. The Shakers had a hard time competing in the industrialized economy that followed the Civil War. With prosperity falling, converts were hard to find.

20th century to the present
By the early 20th century, the once numerous Shaker communities were failing and closing. By mid-century, new federal laws were passed denying control of adoption to religious groups. Today, in the 21st century, the Shaker community that still exists—The Sabbathday Lake Shaker Community—denies that Shakerism was a failed utopian experiment.

Their message, surviving over two centuries in the United States, reads in part as follows: "Shakerism is not, as many would claim, an anachronism; nor can it be dismissed as the final sad flowering of 19th century liberal utopian fervor. Shakerism has a message for this present age–a message as valid today as when it was first expressed. It teaches above all else that God is Love and that our most solemn duty is to show forth that God who is love in the World."

In 1992, Canterbury Shaker Village closed, leaving only Sabbathday Lake open. Eldress Bertha of the Canterbury Village closed their official membership book in 1957, not recognizing the younger people living in other Shaker Communities as members.

On January 2, 2017, Sister Frances Carr died aged 89 at the Sabbathday community, leaving only two remaining Shakers: Brother Arnold Hadd, age 58, and Sister June Carpenter, 77. The Spring/Summer 2019 issue of the Shaker newsletter The Clarion also makes reference to a Brother Andrew. These remaining Shakers hope that sincere newcomers will join them.

Nevertheless, the Shakers at Sabbathday Lake "stressed the autonomy of each local community" and therefore do accept new converts to Shakerism into their community. This Sabbathday Lake Shaker Community receives around two enquiries every week.

Leadership
Four Shakers led the society from 1772 until 1821.
 * 1) Mother Ann Lee (1772–1784)
 * 2) Father James Whittaker (1784–1787)
 * 3) Father Joseph Meacham (1787–1796)
 * 4) Mother Lucy Wright (1796–1821)

After 1821, there was no one single leader, but rather a small nucleus of Ministry elders and eldresses with authority over all the Shaker villages, each with their own teams of elders and eldresses who were subordinate to the Ministry.

The Shaker Ministry continued to build the society after Lucy Wright died in 1821:
 * Elder Ebenezer Bishop (1768–1849), Elder Rufus Bishop (1774–1852), Eldress Ruth Landon (1775–1850), Eldress Asenath Clark (1821–1857).

Subsequent members of the Shaker Ministry included:
 * Elder Daniel Boler (1804–1892), Elder Giles Avery (1815–1890), Eldress Betsy Bates (1798–1869), and Eldress Eliza Ann Taylor (1811–1897).
 * Eldress Polly Reed (1818–1881) was also known as an artist who created Shaker gift drawings such as "A present from Mother Lucy to Eliza Ann Taylor", 1851 (above) in the 1840s and 1850s.
 * Eldress Harriet Bullard (1824–1916)
 * Elder Frederick William Evans (1858–?)
 * Eldress Frances Hall (1947–1957)
 * Eldress Emma King (1957–?)
 * Eldress Gertrude Soule and Eldress Bertha Lindsay (?–early 1990s)
 * Elder Arnold Hadd & Eldress June Carpenter (? – present)

Dualism
Shaker theology is based on the idea of the dualism of God as male and female: "So God created him; male and female he created them" (Genesis 1:27). This passage was interpreted as showing the dual nature of the Creator.

First and second coming
Shakers believed that Jesus, born of a woman, the son of a Jewish carpenter, was the male manifestation of Christ and the first Christian Church; and that Mother Ann, daughter of an English blacksmith, was the female manifestation of Christ and the second Christian Church (which the Shakers believed themselves to be). She was seen as the Bride made ready for the Bridegroom, and in her, the promises of the Second Coming were fulfilled.

Nature of God
Because of the adoptionist view of Christ only becoming divine during his baptism and the dualist idea that God was to be expressed in male and female genders, Shakers are sometimes viewed as being nontrinitarian. However, modern-day Shakers profess the divinity of Christ and claim that Shaker dualism is because "God has no sex in our human understanding of the term; yet being pure spirit He may best be thought of by man with his limited power of comprehension as having the attributes of both maleness and femaleness". The Trinity is not viewed as being false. Instead, Shakers argue that the Trinity has been misinterpreted for being completely masculine. Ann Lee's embodiment of Christ thus completed the Trinity by fulfilling the female aspect of God.

Ethics
Adam's sin was understood to be sex, which was considered to be an act of impurity. Therefore, marriage was abolished within the body of the Believers in the Second Appearance, which was patterned after the Kingdom of God, in which there would be no marriage or giving in marriage. The four highest Shaker virtues were virgin purity, communalism, confession of sin – without which one could not become a Believer – and separation from the world.

Ann Lee's doctrine was simple: confession of sins was the door to the spiritual regeneration, and absolute celibacy was the rule of life. Shakers were so chaste that men and women could not shake hands or pass one another on the stairs.

Equality
Enshrined in Shaker doctrine is a belief in racial equality and gender equality.

Celibacy and children
Shakers were celibate; procreation was forbidden after they joined the society (except for women who were already pregnant at admission). Children were added to their communities through indenture, adoption, or conversion. Occasionally a foundling was anonymously left on a Shaker doorstep. They welcomed all, often taking in orphans and the homeless. For children, Shaker life was structured, safe and predictable, with no shortage of adults who cared about their young charges.

When Shaker youths, girls and boys, reached the age of 21, they were free to leave or to remain with the Shakers. Unwilling to remain celibate, many chose to leave; today there are thousands of descendants of Shaker-raised seceders.

Gender roles
Shaker religion valued women and men equally in religious leadership. The church was hierarchical, and at each level women and men shared authority. This was reflective of the Shaker belief that God was both female and male. They believed men and women were equal in the sight of God, and should be treated equally on earth, too. Thus two Elders and two Eldresses formed the Ministry at the top of the administrative structure. Two lower-ranking Elders and two Eldresses led each family, women overseeing women and men overseeing men.

In their labor, Shakers followed traditional gender work-related roles. Their homes were segregated by sex, as were women and men's work areas. Women worked indoors spinning, weaving, cooking, sewing, cleaning, washing, and making or packaging goods for sale. In good weather, groups of Shaker women were outdoors, gardening and gathering wild herbs for sale or home consumption. Men worked in the fields doing farm work and in their shops at crafts and trades. This allowed the continuation of church leadership when there was a shortage of men.

Worship
Shakers worshipped in meetinghouses painted white and unadorned; pulpits and decorations were eschewed as worldly things. In meeting, they marched, sang, danced, and sometimes turned, twitched, jerked, or shouted. The earliest Shaker worship services were unstructured, loud, chaotic and emotional. However, Shakers later developed precisely choreographed dances and orderly marches accompanied by symbolic gestures. Many outsiders disapproved of or mocked Shakers' mode of worship without understanding the symbolism of their movements or the content of their songs.

Shaker communities
The Shakers built more than twenty communities in the United States. Women and men shared leadership of the Shaker communities. Women preached and received revelations as the Spirit fell upon them. Thriving on the religious enthusiasm of the first and second Great Awakenings, the Shakers declared their messianic, communitarian message with significant response. One early convert observed: "The wisdom of their instructions, the purity of their doctrine, their Christ-like deportment, and the simplicity of their manners, all appeared truly apostolical." The Shakers represent a small but important Utopian response to the gospel. Preaching in their communities knew no boundaries of gender, social class, or education.

Economics
The communality of the Believers was an economic success, and their cleanliness, honesty and frugality received the highest praise. All Shaker villages ran farms, using the latest scientific methods in agriculture. They raised most of their own food, so farming, and preserving the produce required to feed them through the winter, had to be priorities. Their livestock were fat and healthy, and their barns were commended for convenience and efficiency. When not doing farm work, Shaker brethren pursued a variety of trades and hand crafts, many documented by Isaac N. Youngs. When not doing housework, Shaker sisters did likewise, spinning, weaving, sewing, and making sale goods—baskets, brushes, bonnets, brooms, fancy goods, and homespun fabric that was known for high quality, but were more famous for their medicinal herbs, garden seeds of the Shaker Seed Company, apple sauce, and knitted garments (Canterbury). Some communities, especially those in New England, produced maple syrup for sale as well.

Shakers ran a variety of businesses to support their communities. Many Shaker villages had their own tanneries, sold The Shaker goal in their labor was perfection. Ann Lee's followers preserved her admonitions about work:

"'Good spirits will not live where there is dirt.' 'Do your work as though you had a thousand years to live and as if you were to die tomorrow.' 'Put your hands to work, and your heart to God.'"

Mother Ann also cautioned them against getting into debt.

Shaker craftsmen were known for a style of Shaker furniture that was plain in style, durable, and functional. Shaker chairs were usually mass-produced because a great number of them were needed to seat all the Shakers in a community.

Around the time of the American Civil War, the Shakers at Mount Lebanon, New York, increased their production and marketing of Shaker chairs. They were so successful that several furniture companies produced their own versions of "Shaker" chairs. Because of the quality of their craftsmanship, original Shaker furniture is costly. Shakers won respect and admiration for their productive farms and orderly communities. Their industry brought about many inventions like Babbitt metal, the rotary harrow, the circular saw, the clothespin, the Shaker peg, the flat broom, the wheel-driven washing machine, a machine for setting teeth in textile cards, a threshing machine, metal pens, a new type of fire engine, a machine for matching boards, numerous innovations in waterworks, planing machinery, a hernia truss, silk reeling machinery, small looms for weaving palm leaf, machines for processing broom corn, ball-and-socket tilters for chair legs, and a number of other useful inventions. Even prolific Shaker inventors like Tabitha Babbit did not patent their inventions before or after putting them into practice, which has complicated subsequent efforts by 20th century historians to assign priority.

Shakers were the first large producers of medicinal herbs in the United States, and pioneers in the sale of seeds in paper packets. Brethren grew the crops, but sisters picked, sorted, and packaged their products for sale, so those industries were built on a foundation of women's labor in the Shaker partnership between the sexes.

The Shakers believed in the value of hard work and kept comfortably busy. Mother Ann said: "Labor to make the way of God your own; let it be your inheritance, your treasure, your occupation, your daily calling".

Architecture and furnishings
The Shakers' dedication to hard work and perfection has resulted in a unique range of architecture, furniture and handicraft styles. They designed their furniture with care, believing that making something well was in itself an act of prayer. Before the late 18th century, they rarely fashioned items with elaborate details or extra decoration, but only made things for their intended uses. The ladder-back chair was a popular piece of furniture. Shaker craftsmen made most things out of pine or other inexpensive woods and hence their furniture was light in color and weight.

The earliest Shaker buildings (late 18th – early 19th century) in the northeast were timber or stone buildings built in a plain but elegant New England colonial style. Early 19th-century Shaker interiors are characterized by an austerity and simplicity. For example, they had a "peg rail", a continuous wooden device like a pelmet with hooks running all along it near the lintel level. They used the pegs to hang up clothes, hats, and very light furniture pieces such as chairs when not in use. The simple architecture of their homes, meeting houses, and barns has had a lasting influence on American architecture and design. There is a collection of furniture and utensils at Hancock Shaker Village outside of Pittsfield, Massachusetts, that is famous for its elegance and practicality.

At the end of the 19th century, however, Shakers adopted some aspects of Victorian decor, such as ornate carved furniture, patterned linoleum, and cabbage-rose wallpaper. Examples are on display in the Hancock Shaker Village Trustees' Office, a formerly spare, plain building "improved" with ornate additions such as fish-scale siding, bay windows, porches, and a tower.

Artifacts
By the middle of the 20th century, as the Shaker communities themselves were disappearing, some American collectors whose visual tastes were formed by the stark aspects of the modernist movement found themselves drawn to the spare artifacts of Shaker culture, in which "form follows function" was also clearly expressed. Kaare Klint, an architect and furniture designer, used styles from Shaker furniture in his work.

Other artifacts of Shaker culture are their spirit drawings, dances, and songs, which are important genres of Shaker folk art. Doris Humphrey, an innovator in technique, choreography, and theory of dance movement, made a full theatrical art with her dance entitled Dance of The Chosen, which depicted Shaker religious fervor.

The largest collection of Shaker artifacts is the Robert and Virginia Jones Shaker collection at Harmon Museum, in Lebanon, Ohio.

Music

The Shakers composed thousands of songs, and also created many dances; both were an important part of the Shaker worship services. In Shaker society, a spiritual "gift" could also be a musical revelation, and they considered it important to record musical inspirations as they occurred.

Scribes, many of whom had no formal musical training, used a form of music notation called the letteral system. This method used letters of the alphabet, often not positioned on a staff, along with a simple notation of conventional rhythmic values, and has a curious, and coincidental, similarity to some ancient Greek music notation.

Many of the lyrics to Shaker tunes consist of syllables and words from unknown tongues, the musical equivalent of glossolalia. It has been surmised that many of them were imitated from the sounds of Native American languages, as well as from the songs of African slaves, especially in the southernmost of the Shaker communities, but in fact the melodic material is derived from European scales and modes.

Most early Shaker music is monodic, that is to say, composed of a single melodic line with no harmonization. The tunes and scales recall the folksongs of the British Isles, but since the music was written down and carefully preserved, it is "art" music of a special kind rather than folklore. Many melodies are of extraordinary grace and beauty, and the Shaker song repertoire, though still relatively little known, is an important part of the American cultural heritage and of world religious music in general.

Shakers' earliest hymns were shared by word of mouth and letters circulated among their villages. Many Believers wrote out the lyrics in their own manuscript hymnals. In 1813, they published Millennial Praises, a hymnal containing only lyrics.

After the Civil War, the Shakers published hymnbooks with both lyrics and music in conventional four-part harmonies. These works are less strikingly original than the earlier, monodic repertoire. The songs, hymns, and anthems were sung by the Shakers usually at the beginning of their Sunday worship. Their last hymnbook was published in 1908 at Canterbury, New Hampshire.

The surviving Shakers sing songs drawn from both the earlier repertoire and the four part songbooks. They perform all of these unaccompanied, in single-line unison singing. The many recent, harmonized arrangements of older Shaker songs for choirs and instrumental groups mark a departure from traditional Shaker practice.

Simple Gifts was composed in 1848 by Elder Joseph Brackett, on or about the time he moved to the Shaker community at Alfred, Maine. English poet and songwriter Sydney Carter used the song as the basis for a hymn in 1963 "Lord of the Dance", also referenced as "I Am the Dance".

Some scholars, such as Daniel W. Patterson and Roger Lee Hall, have compiled books of Shaker songs, and groups have been formed to sing the songs and perform the dances.

The most extensive recordings of the Shakers singing their own music were made between 1960 and 1980 and released on a 2-CD set with illustrated booklet, Let Zion Move: Music of the Shakers. Other recordings are available of Shaker songs, both documentation of singing by the Shakers themselves, as well as songs recorded by other groups (see external links). Two widely distributed commercial recordings by The Boston Camerata, "Simple Gifts" (1995) and "The Golden Harvest" (2000), were recorded at the Shaker community of Sabbathday Lake, Maine, with active cooperation from the surviving Shakers, whose singing can be heard at several points on both recordings.

Aaron Copland's 1944 ballet score Appalachian Spring, written for Martha Graham, uses the Shaker tune "Simple Gifts" as the basis of its finale. Given to Graham with the working title "Ballet for Martha", it was named by her for the scenario she had in mind, though Copland often said he was thinking of neither Appalachia nor a spring while he wrote it. Shakers did, in fact, worship on Holy Mount in the Appalachians.

Laboring Songs, a piece composed by Dan Welcher in 1997 for large wind ensemble, is based upon traditional shaker tunes including "Turn to the Right" and "Come Life, Shaker Life".

Works inspired by Shaker culture
For a Shaker Seminar held in Massachusetts in 1981, composer Roger Lee Hall wrote a pageant of original Shaker poetry and music titled, "The Humble Heart", featuring singing and dancing by "The New English Song and Daunce Companie".

Shaker lifestyle and tradition is celebrated in Arlene Hutton's play As It Is in Heaven, which is a re-creation of a decisive time in the history of the Shakers. The play is written by Arlene Hutton, the pen name of actor/director Beth Lincks. Born in Louisiana and raised in Florida, Lincks was inspired to write the play after visiting the Pleasant Hills Shaker village in Harrodsburg, Kentucky, a restored community that the Shakers occupied for more than a century, before abandoning it in 1927 because of the inability of the sect to attract new converts.

Robert Newton Peck's 1972 book, A Day No Pigs Would Die, depicts a family that lives by the "Book of Shaker". They are clearly not traditional Shakers, however, as they live in a family unit separate from others, strive for individual success, and have children.

Novelist John Fowles wrote in 1985 A Maggot, a postmodern historical novel culminating in the birth of Ann Lee, and describing early Shakers in England.

Janice Holt Giles depicted a Shaker Community in her novel "The Believers".

In 2004 the Finnish choreographer Tero Saarinen and Boston Camerata music director Joel Cohen created a live performance work with dance and music entitled "Borrowed Light". While all the music is Shaker song performed in a largely traditional manner, the dance intermingles only certain elements of Shaker practice and belief with Saarinen's original choreographic ideas, and with distinctive costumes and lighting. "Borrowed Light" has been given over 60 performances since 2004 in eight countries, recently (early 2008) in Australia and New Zealand, and most recently (2011) in France, Germany, Finland, the Netherlands, and Belgium. In addition to Doris Humphrey, Martha Graham and Tero Saarinen cited above, choreographers Twyla Tharp ("Sweet Fields", 1996) and Martha Clarke ("Angel Reapers", 2011) also set movement to Shaker hymns. Playwright Alfred Uhry collaborated with Martha Clarke on "Angel Reapers" and used Shaker texts as source material. The music of "Angel Reapers" was successfully and uniquely arranged by Music Director Arthur Solari.

In 2009, Toronto-based, American-born poet Damian Rogers released her first volume of poetry, Paper Radio. The lifestyle and philosophy of the Shakers and their matriarch Ann Lee are recurring themes in her work.

Education
New Lebanon, New York, Shakers began keeping school in 1815. Certified as a public school by the state of New York beginning in 1817, the teachers operated on the Lancasterian system, which was considered advanced for its time. Boys attended class during the winter and the girls in the summer. The first Shaker schools taught reading, spelling, oration, arithmetic and manners, but later diversified their coursework to include music, algebra, astronomy, and agricultural chemistry.

Non-Shaker parents respected the Shakers' schooling so much that they often took advantage of schools that the Shaker villages provided, sending their children there for an education. State inspectors and other outsiders visited the schools and made favorable comments on teachers and students.

Modern-day Shakers
Turnover was high; the group reached maximum size of about 5,000 full members in 1840, and 6,000 believers at the peak of the Shaker movement. The Shaker communities continued to lose members, partly through attrition, since believers did not give birth to children, and also due to economics; products hand-made by Shakers could not compete with mass-produced products and individuals moved to the cities for better livelihoods. There were only 12 Shaker communities left by 1920.

In 1957, after "months of prayer", Eldresses Gertrude, Emma, and Ida, leaders of the United Society of Believers in Canterbury Shaker Village, voted to close the Shaker Covenant, the document which all new members need to sign to become members of the Shakers in Canterbury Shaker Village.

In 1988, speaking about the three men and women in their 20s and 30s who had become Shakers and were living in the Sabbathday Lake Shaker Village, Eldress Bertha Lindsay of the other community, the Canterbury Shaker Village, disputed their membership in the society: "To become a Shaker you have to sign a legal document taking the necessary vows and that document, the official covenant, is locked up in our safe. Membership is closed forever."

However, Shaker covenants lack a "sunset clause" and today's Shakers of Sabbathday Lake Shaker Village welcome sincere new converts to Shakerism into the society:

"If someone wants to become a Shaker, and the Shakers assent, the would-be member can move into the dwelling house. If the novices, as they are called, stay a week, they sign an articles [sic] of agreement, which protects the colony from being sued for lost wages. After a year, the Shakers will take a vote whether to allow the novice in, but it takes another four years to be granted full Shaker status in sharing in the colony's finances and administrative and worship decisions."

On January 2, 2017, Sister Frances Carr died aged 89 at the Sabbathday community, leaving only two remaining Shakers: Brother Arnold Hadd, age 58, and Sister June Carpenter, 77. In the Spring/Summer 2019 issue of the Shaker newsletter The Clarion, the current membership was given as Brother Arnold, Sister June, and Brother Andrew. These remaining Shakers hope that sincere newcomers will join them.

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User:Hajhouse

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