Archives of the Universe by Marcia Bartusiak

Author:Marcia Bartusiak [Bartusiak, Marcia]
Language: eng
Format: epub
ISBN: 978-0-307-51323-6
Publisher: Knopf Doubleday Publishing Group
Published: 2004-08-14T16:00:00+00:00

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40 / Beyond the White Dwarf

Within two decades of the discovery of the extremely dense white dwarf star, theorists working with the new laws of relativity and quantum mechanics were astonished to find that dying stars might face even stranger fates, if they had enough mass.

The first steps toward this realization were taken in 1930, during a sea voyage from India. Nineteen-year-old Subrahmanyan Chandrasekhar, while traveling to England to begin his graduate studies with Ralph Fowler at Cambridge University, explored the physics of white dwarfs and came to realize that velocities for some of the electrons in the dense stellar nugget would approach the speed of light. That meant it was necessary to apply the rules of special relativity to the star’s behavior. Fowler had earlier shown (see Chapter 39) that the pressure from electrons, tightly packed in the compact star at a density of a ton per cubic inch, keeps a white dwarf intact. But could this go on forever? What happens, asked the young student from India, if a white dwarf is even more dense?

Chandrasekhar concluded that there is a critical limit to the mass of a white dwarf (now known to be 1.4 solar masses). If the dwarf is more massive, it collapses, overcome by the extreme pressure of gravity. In 1931 he published this result in a brief paper entitled “The Maximum Mass of Ideal White Dwarfs” in the Astrophysical Journal. The paper’s abstract summarized it succinctly:

The theory of the polytropic gas spheres in conjunction with the equation of state of a relativistically degenerate electron-gas leads to a unique value for the mass of a star built on this model. This mass (= 0.91Θ [solar mass]) is interpreted as representing the upper limit to the mass of an ideal white dwarf.23

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