The Astrophysics Spectator
The Astrophysics Spectator
The brown dwarfs and the giant gaseous planets are bodies of hydrogen and helium that are too light to burn hydrogen in thermonuclear fusion. These bodies are supported by electron degeneracy pressure. With only gravitational potential energy to dissipate, the giant gaseous planets rapidly grow cold. The larger brown dwarfs, because of their greater mass and their ability to burn deuterium and lithium, remain warm longer than the giant gaseous planets, but they, too, eventually grow cold and dark.
The distinction between brown dwarfs and giant gaseous planets is technical: the former burns deuterium, and the latter does not. As a practical matter, however, the burning of deuterium does not have a big impact on the structure and appearance of brown dwarfs. The primary physics in both brown dwarfs and giant gaseous planets is their common chemical composition, the electron degeneracy pressure at their cores, and the absence of significant power generation. For this reason, theorists who study one generally study the other.
The articles given below are generally review articles of the physics. Much of the research is on the chemical composition of and the cloud formation within the atmospheres of these bodies. These calculations provide the direct link to the observations of these bodies. Because the first brown dwarf was observed in 1989, the bulk of the research on these objects is recent.
Two articles describe the physics of brown dwarfs and giant gaseous planets. The first, Theory of Low-Mass Stars and Substellar Objects (Chabrier and Baraffe 2000) discusses objects ranging from 1 solar mass down to the mass of Jupiter. This paper is concerned with the evolution, structure, and appearance of these objects. The second, Theory of Giant Planets (Hubbard, Burrows, and Lunine 2002), is more concerned with the evolution of the giant gaseous planets, although it includes the evolution of the brown dwarfs. The formation and evolution of Saturn and Jupiter are discussed in detail in this article. It also discusses the effect of stellar radiation on a giant gaseous planet, which is relevant for the extrasolar planets found orbiting close to their parent stars.
The atmospheres of brown dwarfs are discussed in Model Atmospheres of Very Low Mass Stars and Brown Dwarfs (Allard et al. 1997). The article discusses how molecules and condensates within the atmospheres of M dwarf stars and brown dwarfs affect cooling and create the spectra observed for these bodies.
The system for classifying stars by the line patterns in their spectra has been extended to the brown dwarfs with the introduction of the L and T spectral types. These two types are described in the article New Spectral Types L and T (Kirkpatrick 2005).
Allard, France, Hauschildt, Peter H., Alexander, David R., and Starrfield, Sumner. “Model Atmospheres of Very Low Mass Stars and Brown Dwarfs.” In Annual Reviews of Astronomy and Astrophysics, edited by G. Burbidge, A. Sandage, and F. Shu, vol. 35. Palo Alto, California: Annual Reviews, 1997: 137–177.
Chabrier, Gilles, and Baraffe, Isabelle. “Theory of Low-Mass Stars and Substellar Objects.” In Annual Reviews of Astronomy and Astrophysics, edited by G. Burbidge, A. Sandage, and F. Shu, vol. 38. Palo Alto, California: Annual Reviews, 2000: 337–377.
Hubbard, W.B., Burrows, A., and Lunine, J.I. “Theory of Giant Planets.” In Annual Review of Astronomy and Astrophysics, edited by G. Burbidge, A. Sandage, and F.H. Shu, vol. 40. Palo Alto, California: Annual Reviews, 2002: 103–136.
Kirkpatrick, J. Davey. “New Spectral Types L and T.” In Annual Reviews of Astronomy and Astrophysics, edited by R. Blandford, G. Burbidge, J. Kormendy, and E. Van Dishoeck, vol. 43. Palo Alto, California: Annual Reviews, 2005: 195–245.
