The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
(c)1998-2002; (c)2002 by Gale. Gale is an imprint of The Gale Group, Inc., a division of Thomson Learning, Inc. Gale and Design and Thomson Learning are trademarks used herein under license.
The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
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The existence of brown dwarfs was first suggested in the 1930s, when observers at Swarthmore College noted that some stars followed paths across the sky that deviated from their predicted courses. Rather than moving in a straight line, these stars oscillated slightly about a steady course. Astronomers began to suspect that these "wobbles" were caused by companion objects to the stars that were invisible to ordinary telescopes because they were too faint to see. In 1975 American astronomer Jill Tarter (1944-) dubbed these objects "brown dwarfs" because she theorized they were akin to red dwarf stars, but were darker and smaller.
A brown dwarf is thought to be a ball of matter that goes through the early stages of stellar evolution but fails to complete the process of becoming an actual star. It condenses out of a small quantity of dust and gas, but does not acquire enough mass to produce the tremendous pressure required to initiate nuclear fusion, which makes stars bright and hot. According to astrophysical theory, an object with less than eight percent the mass of the Sun cannot become a star. Very low-mass brown dwarfs will likely be more akin to planets than stars.
Beginning in the 1970s, David McCarthy, an astronomer at the University of Arizona, made infrared observations to search for these objects (because they are cool and should emit most of their radiation in the infrared part of the spectrum). He and his colleagues have discovered a number of objects that could be brown dwarfs, several in the Pleiades star cluster, but no irrefutable evidence for their existence was found.
Definitive evidence for the existence of substellar objects did finally emerge. In 1992, astronomer Alexander Wolszczan discovered two planets orbiting a pulsar. In 1995, astronomers Michel Mayor and Didier Queloz announced the existence of a planet around the star 51 Pegasi. Returning to the technique of analyzing small variations in the star's motion, astronomer Geoffrey Marcy and his collaborators confirmed the result. Marcy and other astronomers have now accumulated evidence for the existence of brown dwarfs or planets around a number of other stars. Our solar system, it now seems, is far from unique.