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Star

The Fate Of The Sun

Our four stars illustrate the four possible fates of the stars: black holes, neutron stars, white dwarfs, and red dwarfs. The Sun will end its life as a hot-but-faint white dwarf, an object no larger than the earth, and like a dying ember in a campfire it will gradually cool off and fade into blackness. Space is littered with such dead suns.

In its death throes, five billion years from now, the Sun will engulf Mercury, broil Venus, and wipe every vestige of life off the earth. Alnilam will go much more violently; if it has planets, they will be vaporized by the supernova. In both cases, though, an expanding cloud of gas will be flung into space. This cloud will be rich in heavy elements, and there would be no such thing as iron atoms floating through space were it not for stars like Alnilam that create them in their central furnaces.

Stars form from these cold, dark clouds, and so do any planets that form around the stars. The Sun and its planets are second-generation products of our Galaxy, and much of the material that went into making the Sun, the earth, and you was once in the center of some distant and long-dead Alnilam. The theme begun by those distant stars has been picked up by the present generation, and five billion years from now, the Sun in turn will return some of its products to space. Sometime after that, the cycle will begin anew.

Resources

Periodicals

Kaler, James B., "The Brightest Stars in the Galaxy." Astronomy (May 1991): 31.

Terrell, Dirk, "Demon Variables." Astronomy (October 1992): 35.

Jeffrey C. Hall

KEY TERMS

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Core: —The central region of a star, where thermonuclear fusion reactions take place that produce the energy necessary for the star to support itself against its own gravity.
End state: —One of the four possible ways in which a star can end its life. Stellar end states include black holes, neutron stars, white dwarfs, and red dwarfs.
Hydrostatic equilibrium: —The condition in which the gas pressure at a given place within a star exactly counterbalances the weight of the overlying material. Such a star is stable, neither expanding nor contracting significantly.
Laws of stellar structure: —The four mathematical formulae that describe the internal structure of a star. Using these laws, an astronomer can construct a stellar model that reproduces the observed properties of the star and that describes the temperature, pressure, and thermonuclear reactions, among other things, taking place inside the star.
Luminosity: —The rate at which a star radiates energy (i.e., the star's brightness). The brightest stars are 50,000 times more luminous than the Sun, while the faintest may be only a few thousandths as luminous.
Mass-luminosity relation: —Describes the dependence of a star's brightness (luminosity) on its mass, and expressed in the form L = 3.5M. More massive stars have stronger gravity, and therefore must produce and radiate energy more intensely to counteract it, than less massive stars.
Photosphere: —The thin layer at the base of a star's atmosphere where most of the visible light escapes. Light below the photosphere is absorbed and scattered by the overlying material before it can escape to space.

Additional topics

Science EncyclopediaScience & Philosophy: Spectroscopy to Stoma (pl. stomata)Star - Energy Generation, Stellar Models, Mass: The Fundamental Stellar Property, Four Stars, Variable Stars - The nature of the stars