lanetary and potentially habitable zone orbits of this system, with a table of basic orbital and physical characteristics.)
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.
University of California at Berkeley astronomer Ben R. Oppenheimer, who helped to discover a 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 San Francisco State University 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.
The following table includes all star systems known to be located within 10 light-years (ly), plus more bright stars within 10 to 20 ly, of 23 Librae.
|Star System||Spectra &|
|CD-26 10870||K3-4 V||6.0|
|L 624-20||M3.5 V||9.1|
|CD-26 10849||G8-K0 V||9.8|
|* plus bright stars *||. . .|
|BD-15 4042 A||K0-1 V-IV||16|
|BD-15 4042 B||K0-2 V-IV||19|
Alpha2 Librae A
Alpha2 Librae B
|BD-15 3924||G6 V||18|
|54 Hydrae 3||F0-2 V-III |
Try Professor Jim Kaler's Stars site for other information about 23 Librae at the University of Illinois' Department of Astronomy. John Whatmough developed illustrated web pages on this system in Extrasolar Visions.
Up-to-date technical summaries on these stars can be found at: Jean Schneiders's Extrasolar Planets Encyclopaedia; the Astronomiches Rechen-Institut at Heidelberg's ARICNS; and the NASA Star and Exoplanet Database. Additional information may be available at Roger Wilcox's Internet Stellar Database.
The ancient Greeks grouped the stars of Libra with Constellation Scorpius, the Scorpion. To the later Romans, however, Constellation Libra represent "the Scales of Justice" held by Julius Caesar. For later peoples, these scales became associated with Virgo as the Goddess of Justice, proving that political power is indeed fleeting. . For more information about the stars and objects in this constellation, go to Christine Kronberg's Libra. For an illustration, see David Haworth's Libra.
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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