Luhman 16 (WISE 1049-5319) ab
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On January 29, 2014, a team of astronomers using the European Southern Observatory's Very Large Telescope (VLT) announced that they had imaged weather patterns produced by very hot clouds on Luhman 16 b, but not Luhman A, which has apparently has a featureless atmosphere in the wavelengths observed. Using the CRIRES instrument on the VLT, the astronomers were able to measure the relative depth of the lighter and darker patches on the substellar object using doppler shift variations. Among other weather, the brown dwarf may have been experiencing rains of silicate rock and molten iron, otherwise kept aloft by "vigorous atmospheric motions" (MPIA science release, ESO news release, David Dickinson, Universe Today, January 30, 2014, and Ken Croswell, Physics World, January 29, 2014).
Ian J. M. Crossfield,
Larger and jumbo surface maps.
Due to their close proximity to the
Solar System, weather patterns
on Luhman 16 b were recently imaged
as the brown dwarf rotated once on
its axis (more).
On December 4, 2013, a team of astronomers revealed that astrometric measurements indicate that Luhman 16 ab has another major unseen companion orbiting one of two brown dwarf components of the binary system. If the unseen companion is a planet of 10 Jupiter-masses, then it has an orbital period between two months and one year. The team also claimed to have obtained a more precise parallax of 6.6 +/-0.1 light-years (2.020+/-0.019 pc) from our Sun, Sol (Boffin et al, 2013).
Digitized Sky Survey 2,
Larger and jumbo wide starfield images
centered around Luhman 16 ab.
Luhman 16 ab are not visible to
the unaided Human eye, although
they may lie only around 6.5
light-years away from Sol (more).
This extremely dim pair of celestial objects contains the closest known brown dwarfs to Sol, as of March 11, 2013. Designated WISE J104915.57-531906 (but shortened to WISE 1049-5319) but also referred as Luhman 16 ab (in honor of its discoverer), it is located about 6.5 +/- 0.5 light-years away. It can be found in the southern part (10:49:15.57-53:19:06) of Constellation Vela, the Sails, in the southern hemisphere -- southeast of Phi, Kappa (Markeb), and Gamma Velorum (Regor), southwest of Mu Velorum; and northeast of Aspidiske (Iota Carinae) and Avior (Epsilon Carinae), and northwest of the Keyhole Nebula (NGC 3324).
On March 11, 2013, an astronomer revealed the discovery of these brown dwarfs using infrared images collected by NASA's Wide-field Infrared Survey Explorer (WISE) during a 13-month period ending in 2011, which every point in the sky was observed two to three times. An extremely dim object with high proper motion was found in several images, when archival observations from older telescopic sources were consulted. Further observation revealed that the object was actually a binary system (NASA news release; PSU news release; and Kevin L. Luhrman, 2013; and Burgasser et al, 2013).
The Brown Dwarfs
Based on a spectroscopy, the brighter object is currently classed as a L 8+/-1 dwarf, while its dimmer secondary is probably near the L and T threshold. The two high-proper-motion objects appear to be separated by around three AUs (1.5 arcseconds) at present (Kevin L. Luhrman, 2013).
Larger illustration: Sol; M,L,T dwarfs;
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 (more; and Kevin L. Luhman, 2013).
Although brown dwarfs lack sufficient mass (at least 75-80 Jupiters) to ignite core hydrogen fusion, the smallest true stars (red dwarfs) can have such cool atmospheric temperatures (below 4,000° K) that it is difficult to distinguish them from young brown dwarfs. While Jupiter-class planets may be much less massive than brown dwarfs, they are about the same diameter and may contain many of the same atmospheric molecules.
Brown Dwarfs or Planets?
When brown dwarfs were just a theoretical concern, astronomers differentiated those hypothetical objects from planets by how they were formed. If a substellar object was formed the way a star does, from a collapsing cloud of interstellar gas and dust, then it would be called a brown dwarf. If it was formed by gradually accumulating gas and dust inside a star's circumstellar disk, however, it was called a planet. Once the first brown dwarf candidates were actually found, however, astronomers realized that it was actually quite difficult to definitely rule on the validity of competing hypotheses about how a substellar object was actually formed without having been there. This problem is particularly difficult to resolve in the case of stellar companions, objects that orbit a star -- or two.
Astronomer Ben R. Oppenheimer, who helped to discover the other nearby brown dwarf, Gliese 229 b, is part of a growing group that would like to define a brown dwarf as an substellar object with the mass of 13 to 80 (or so) Jupiters. While these objects cannot fuse "ordinary" hydrogen (a single proton nucleus) like stars, they have enough mass to briefly fuse deuterium (hydrogen with a proton-neutron nucleus). Therefore, stellar companions with less than 13 Jupiter masses would be defined as planets.
Other prominent astronomers, such as astronomer Geoffrey W. Marcy who also has helped to discover many extrasolar planets, note that there may in fact be many different physical processes that lead to the formation of planets. Similarly, there may also be many different processes that lead to the creation of brown dwarfs, and some of these may also lead to planets. Hence, more observational data may be needed before astronomers can determine how to make justifiable distinctions in the classification of such substellar objects.
Vela is a large constellation of the southern hemisphere, with no stars labelled as alpha and beta as it was once part of a larger constellation. Together with Carina, Puppis, and Pyxis, Vela forms the ancient constellation of Argo Navis, the ship of the Argonauts. After the larger constellation was broken up, the brightest stars were not assigned to Vela, but no other bright stars were reassigned using traditional notation. For more information and illustrations of Constellation Vela, go to Christine Kronberg's Vela. For another illustration, see David Haworth's Vela.
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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