Brown dwarfs within 10 parsecs
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Larger and jumbo illustrations: Sol; M,L,T dwarfs; & Jupiter.
At one billion years in age, large brown dwarfs are reddish
like the smallest M-type stars, but cooler, dimmer T-dwarfs
are more magenta in hue. At least 48 brown dwarfs may be
located within 10 parsecs of Sol (more).
Larger and jumbo illustrations (source).
On September 27, 2012, astronomers using the
Wide-field Infrared Survey Explorer (WISE),
a space telescope, had announced the
discovery of 13 very cool, Y-class brown
dwarfs, including one (WISE 1541-2250)
possibly only some nine light-years from
Sol in Constellation Lyra (update -- more).
By July 2013, astronomers had found at least 43 brown dwarfs within 10 parsecs (32.6 light-years) of Sol, although these objects are extremely dim compared to OBAFGK stars. Some astronomers believe that brown dwarfs may be as numerous as stars in the Milky Way. Unfortunately, none are bright enough to observe with the unaided Human eye in Earth's night sky.
Spectral Populations of Brown Dwarfs
|Spectral Type||Number within |
|T||29-32+||Epsilon Indi ba|
Larger and jumbo illustrations (source).
As of April 25, 2014, astronomers using
Wide-field Infrared Survey Explorer (WISE),
a space telescope, have identified at
least 10 very cool, Y-class brown dwarfs
within 40 light-years of Sol (more).
According to some theorists, a celestial object with a mass of less than about 75 Jupiter-masses -- around seven percent of Sol's mass -- cannot sustain significant nuclear fusion reactions in its core and so will not destroy the lithium in its atmosphere. Hence, this mass threshold divides brown dwarfs from the smallest, dimmest red dwarf stars. Establishing a lower mass limit for brown dwarfs has proven to be more difficult. Some astronomers would like to set the minimum mass limit at 13 Jupiter-masses, because less massive objects cannot even fuse deuterium.
© Anglo-Australian Telescope Board
(Image by Chris Tinney)
Wide field, "true-color" image
with satellite trail.
Brown dwarfs are actually
reddish, like the binary
DENIS 1228-1547, or
magenta in color for the
cooler and dimmer T-dwarfs
that are rich in methane.
Although brown dwarfs are similar in size to Jupiter, they are much more massive and dense enough in their cores to produce their own light (mostly infrared wavelengths), whereas Jupiter shines with reflected light from the Sun. When brown dwarfs are very young, they are relatively luminous because they do generate some radiative energy from the fusion of deuterium ("heavy hydrogen") into helium nuclei, which is used up in a few tens of millions of years. Subsequently, brown dwarfs glow much more feebly from the heat generated by the release of gravitational energy as they slowly contract. By definition, the object's core temperature must be less than three million degrees, as that is the critical temperature required for substantial nuclear reactions to take place. However, surface temperature is dependent on its mass, which will be lower for lower mass objects. Hence, brown dwarfs are expected to have a surface temperature around 1,000 K and cool down as they get older, as initial nuclear fusion of deuterium at the beginning of its life cannot be sustained very long. Because of their low surface temperature, brown dwarfs are not very luminous (more).
Larger and jumbo illustrations: Sol; M,L,T dwarfs; & Jupiter. .
In near-infrared, M and L dwarfs are slightly orange or red
compared to Sol, while methane-rich T dwarfs are bluish
from methane absorption of green and red light, similar to
The smaller red dwarf stars, brown dwarfs, and gas giant planets like Jupiter all have approximately the same size, less than a tenth of Sol's diameter. At around one billion years in age, red dwarf stars and L-type brown dwarfs are red, while the less massive T dwarf is dimly magenta, due to the absorption of green wavelengths by sodium and potassium atoms. In near-infrared light, red dwarfs and L dwarfs are slightly orange or red compared to the Sun, but methane-rich T dwarfs are distinctly blue due to a lack of light in the green and red portions of the spectrum caused by absorption from methane. Methane is also abundant in the atmosphere of Jupiter and this gas, along with clouds and bands of other complex molecules, gives rise to alternating patches of pink and blue on Jupiter and possibly the cooler brown dwarfs as well (Kirkpatrick et al's L&T Dwarfs; M,L, and T dwarf classification; and Adam J. Burgasser's T-Dwarfs page.)
Jeffrey L. Linsky,
Brown dwarfs, like Van
Biesbroeck's Star (Gliese
752 B) have less than 20
percent of Sol's mass and
so can transport core heat
through convection only,
unlike its larger and brighter
companion Gl 752 A (more).
Because a brown dwarf does not have a strong central source of nuclear energy, its interior should be a rapid "boiling," convective motion. 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. Astronomers believe that this magnetic field can create strong flares. As turbulent magnetized hot material beneath a brown dwarf's surface conducts heat to its atmosphere, it would allows electric currents to flow and produce an X-ray flare, as has been detected from LP 944-20. The absence of X-rays from LP 944-20 during non-flaring periods suggest that the million-degree Celsius upper atmosphere, or corona, created by flares disappears as its surface temperature cools below around 2,773 degrees K and becomes electrically neutral.
Brown dwarfs with at
least 0.07 Solar-mass
can host planets in
their habitable zones
for two to 10 billion
years, but such planets
would orbit with two to
three Roche radii of
being ripped apart by
tidal forces from their
host brown dwarf's
Some have speculated whether it is possible for a planet orbiting a brown dwarf to have liquid water on its surface for a period sufficiently long enough to host the development of Earth-type life (i.e., at least three billion years for the development of complex multicellular plants and animals). While brown dwarfs cool off with time because they lack self-sustaining fusion reactions like stars, calculations indicate that the time during which the temperature of a rocky planet remains in the liquid water range during the fading of its parent brown dwarf can be modelled as a function of the brown dwarf's mass and the planet's orbital distance. Using evolutionary models for brown dwarfs and radiative flux criteria for setting the inner and out edges of a brown dwarf potential habitable zone (from the inner "moist stratosphere" limit to the outermost distance for greenhouse heating from atmospheric Carbon Dioxide) (Kastings et al, 1993), durations of planetary habitability range from 0.5 to two billion years for a brown dwarf mass of 0.03 Solar-mass to two to 10 billion years for a brown dwarf mass of 0.07 Solar-mass. Unfortunately, such planets must orbit their within close proximity of the orbital Roche radius (within two to three Roche radii) of their host brown dwarf, near where tidal forces from a brown dwarf's gravity will rip apart the planet. In addition, such planets or, at least, their atmospheres could be destroyed during the hottest period of a brown dwarf's life soon after formation (Andreeshchev and Scalo, 2004; and Phil Gilster, Centauri Dreams blog, June 21, 2010).
Nearby Stars by Brightness, Spectra, and Distance
The following brown dwarfs are located within 33 light-years (ly), or 10 parsecs, of Sol.
|NStar / |
|6.5 +/- 0.5||Luhman 16 a||L 8 +/-1 V||<0.08||Vela||Brown dwarf binary|
|6.5 +/- 0.5||Luhman 16 b||L/T V||<0.08||Vela||Brown dwarf, sep(ab)=3 AUs|
|7.2 +0.8/-0.7||WISE 0855-0714||Y? V||<0.08||Hydra||Brown dwarf, coldest (4/25/14)|
|9.1 +4.2/-2.0||WISE 1541-2250||Y0 V||<0.08||Lyra||(NASA science news and news release; Cushing et al, 2011; and Kirkpatrick et al, 2011)|
|11.1 +2.3/-1.3||WISE 1506-7027||T6 V||<0.08||Apus||(Marsh et al, 2012, Table 3)|
|>11.1||WISE 1405+5534||Y0 Vp?||<0.08||Draco||(Marsh et al, 2012, Table 3)|
|11.8||Epsilon Indi ba||T1 V||0.043~||Indus||Methane|
|11.8||Epsilon Indi bb||T6 V||0.028~||Indus||Methane|
|12.1 +5.2/-1.3||WISE 0350-5658||Y1 V||<0.08||Horologium||(Marsh et al, 2012, Table 3)|
|12.6 +/- 0.7||SCR 1845-6357 b||T4.5-6.5 V||0.009 - 0.065||Pavo||Methane (Henry et al, 2006; ESO press release; and Biller et al, 2006)|
|13 +/- 2||UGPS 0722-05||T9 V||<0.03||Monoceros||Methane, UGPS J072227.51-054031.2, UGPS J0722-05 (Lucas et al, 2010; and Cushing et al, 2011)|
|13.2 +/- 0.1||DENIS 1048-39||M8.5 V||0.06-0.09||Antlia||M (red dwarf) star?|
|13.7 +3.9/-2.0||WISE 0410+1502||Y0 V||<0.08||Taurus||(Marsh et al, 2012, Table 3)|
|16 +/- 1||DENIS / DEN 0817-6155||T6 V||<0.08||Carina||Methane (Artigau et al, 2010)|
|16.2 +/- 0.3||DENIS / DEN 0255-4700||L7.5 V||0.07~||Eridanus||(NOAO press release)|
|16.3||LP 944-20||M9.0 V||0.056-0.064||Fornax||Flares|
|16 +/- 2||WISE J163940.83-684738.6||Y? V||<0.08||Triangulum Australis||(Tinney et al, 2012)|
|16.0 +3.3/-2.0||WISE 0254+0223||T8-10 V||<0.08||Cetus||Methane (Marsh et al, 2012, Table 3; and Scholz et al, 2011)|
|16 +5/-4||WISE J052126.29+102528.4||T7.5 V||<0.08||Orion||(Bihain et al, 2013)|
|~17||2MASS J09393548-2448279 AB?||T8.5 V |
|0.06-0.08||Antlia||Methane binary? (Burgasser et al, 2008; Leggett et al, 2007; and Tinney et al, 2005)|
|17 - 38||WISE J2209+2711||Y0 V||17 - 38||Pegasus||(Cushing et al, 2014)|
|18 - 30||WISEPC J045853.90+643451.9||T9 V||<0.08||Camelopardalis||Methane (Mainzer et al, 2010)|
|18.5 +/-0.05||2MASS 1835+3259||M8.5 V||0.07||Hercules||(RECONS; and (Reid et al, 2003?)|
|18.6 +/- 3.9||WISE 1741+2732||T9 V||<0.08||Hercules||(Kirkpatrick et al, 2011, Table 7)|
|18.7 +/-0.3||2MASS 0415-0935||T8 V||<0.08||Eridanus||Methane (press release; and Liebert et al, 2002)|
|18.8||Gliese 229 b||T6.5 V||0.025-0.065||Lepus||Methane, sep=39 AUs|
|19.3||Gliese 570 d||T7-8 V||0.05+/-0.02||Libra||Methane, a(ABC-d)=1,500+ AUs|
|18.9 +3.6/-2.0||WISE 1741+2553||T9-10 V||<0.08||Hercules||Methane (Marsh et al, 2012, Table 3; and Scholz et al, 2011)|
|19.2 +4.6/-2.0||WISE 0359-5405||Y0 V||<0.08||Reticulum||(Marsh et al, 2012, Table 3)|
|>19.6||WISE 1541-2250||Y0.5 V||<0.08||Norma||(Marsh et al, 2012, Table 3)|
|>19.6||WISE 1738+2732||Y0 V||<0.08||Hercules||(Marsh et al, 2012, Table 3)|
|20.0 +/-0.5||2MASS 0937+2931||T6 Vp||<0.08||Sextans||Methane (Adam J. Burgasser, 2004; and Liebert et al, 2002)|
|20.9 +/-1.0||SIMP J013656.5093347||T2-3 V||<0.08||Pisces||Methane (Artigau et al, 2006)|
|21.46 +/- 6.0||WISE 0254-0223||T8 V||<0.08||Cetus||(Kirkpatrick et al, 2011, Table 7)|
|22 - 39||WISE J0943+3607||T9.5 V||<0.08||Carmelopardus||(Cushing et al, 2014)|
|23.9 +/-0.1||2MASS J15074769-1627386||L5 V||<0.08||Libra||(Reid et al, 2000)|
|24.5 +14/-5.9||WISE 2056+1459||Y0 V||<0.08||Equuleus||(Marsh et al, 2012, Table 3)|
|25.7 +/- 5.5||SDSS J1416+13 a||L6 V||>0.03||Boötes||Binary, (Bowler et al, 2010)|
|25.7 +/- 5.5||SDSS J1416+13 b||T(-Y?) V||~0.03||Boötes||Binary, (Burgasser et al, 2010; R.-D. Scholz, 2010; Burningham et al, 2010, and Schmidt et al, 2010)|
|25.7 +/- 5.5||WISE J2000+3629||T8 V||13 to 26||Cygnus||(Cushing et al, 2014)|
|28.6 +/-0.2||2MASS J00361617+1821104||L3.5 V||<0.08||Pisces||(Reid et al, 2000)|
|28.7-31.3||CFBDS J005910.90-011401.3||T9 V||<0.08||Pisces||(Marocco et al, 2010; and Delorme et al, 2008)|
|29.6 +/-0.5||2MASS 0727+1710||T7 V||<0.08||Gemini||Methane (Burgasser et al, 2002; and Liebert et al, 2002)|
|30.0 +/- 7.5||WISE 1647+5632||L9 Vp||<0.08||Draco||(Kirkpatrick et al, 2011, Table 7)|
|32.6 - 34.6||ULAS J133553.45+113005.2||T9 V||<0.08||Virgo||(Marocco et al, 2010; and Burningham et al, 2008)|
|... >32.6 ...||(beyond 10 pc)|
|33.4 +/- 0.4||2MASS 0559-1404||T5 V||<0.08||Lepus||Methane (Burgasser et al, 2000; and Liebert et al, 2002)|
|34.0 +1.8/-1.6||2MASS 1237+6526||T6.5 Ve||<0.08||Draco||Methane (Burgasser et al, 1999; and Liebert et al, 2002)|
|34.1 +8.5/-8.4||WISE J203042.79+074934.7||T2 V||<0.08||Aquila||(Bihain et al, 2013)|
|34.4 +/1.3/-1.4||2MASS 1047+2124||T6.5 V||<0.08||Leo||Methane (Burgasser et al, 2000; Burgasser et al, 1999; and Liebert et al, 2002)|
|34.4 +/-0.4||2MASS J08251968+2115521||L7.5 V||<0.08||Cancer||(Kirkpatrick et al, 2000)|
|34.8 +1.3/-1.4||2MASS J02431371-2453298||T6 V||<0.08||Cetus||Methane (Burgasser et al, 2002; and Liebert et al, 2002)|
|40.8 +10.1/-9.5||WISE J045746.08-020719.2||T1.5 V||<0.08||Eridanus||(Bihain et al, 2013)|
|42.4 +/-2.2||LHS 102 bc||L5 V||<0.08||Phoenix||GJ 1001 bc (Henry et al, 2006; and Goldman et al, 1999)|
Summary information on AFGK "bright" stars, red dwarf stars, white dwarfs, and all stars and related celestial objects within 10 parsecs are also available.
Up-to-date technical summaries on these objects may be available from: the Research Consortium on Nearby Stars (RECONS) list of the 100 Nearest Star Systems, NASA's NStar Database, and the Astronomiches Rechen-Institut at Heidelberg's ARCNS. Additional information may be available at Roger Wilcox's Internet Stellar Database.
For more information about stars including spectral and luminosity class codes, go to ChView's webpage on The Stars of the Milky Way.
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