Book contents
- Frontmatter
- Contents
- List of Focus Elements
- List of Tables
- Preface
- 1 Light of the Sun
- 2 Gravity and Motion
- 3 Atomic and Subatomic Particles
- 4 Transmutation of the Elements
- 5 What Makes the Sun Shine?
- 6 The Extended Solar Atmosphere
- 7 Comparisons of the Sun with Other Stars
- 8 The Lives of Stars
- 9 The Material Between the Stars
- 10 New Stars Arise from the Darkness
- 11 Stellar End States
- 12 A Larger, Expanding Universe
- 13 Birth, Life, and Death of the Universe
- Quotation References
- Author Index
- Subject Index
- Plate section
8 - The Lives of Stars
Published online by Cambridge University Press: 05 February 2013
- Frontmatter
- Contents
- List of Focus Elements
- List of Tables
- Preface
- 1 Light of the Sun
- 2 Gravity and Motion
- 3 Atomic and Subatomic Particles
- 4 Transmutation of the Elements
- 5 What Makes the Sun Shine?
- 6 The Extended Solar Atmosphere
- 7 Comparisons of the Sun with Other Stars
- 8 The Lives of Stars
- 9 The Material Between the Stars
- 10 New Stars Arise from the Darkness
- 11 Stellar End States
- 12 A Larger, Expanding Universe
- 13 Birth, Life, and Death of the Universe
- Quotation References
- Author Index
- Subject Index
- Plate section
Summary
Main-Sequence and Giant Stars
The Hertzsprung–Russell Diagram
Once the luminosity of stars was obtained from their brightness and measurements of their distance, astronomers were able to show that most stars exhibit a systematic decrease in luminosity as one progresses through the spectral sequence O, B, A, F, G, K, M. (These spectral types are described in Section 7.4.) This progression is exactly what we would expect because the spectral sequence also denotes a scale of decreasing stellar temperatures, and the luminosity of a radiating body depends strongly on temperature.
The luminosity drop is illustrated in the famous Hertzsprung–Russell (H–R) diagram of luminosity or absolute magnitude plotted against the spectral class or effective temperature. The diagram's name derives from the Danish astronomer Ejnar Hertzsprung, who first plotted such diagrams for the Pleiades and Hyades star clusters, and the American astronomer Henry Norris Russell, who next published early versions of this diagram for both cluster and noncluster stars (Fig. 8.1).
Most stars, including the Sun, lie on the main sequence that extends diagonally from the upper left to the lower right, or from the high-luminosity, high-temperature blue stars to the low-luminosity, low-temperature red stars. The stars on the main sequence are the most common type in the Milky Way, constituting about 90 percent of its stars.
The Stefan–Boltzmann law describes the general characteristics of the H–R diagram. This expression indicates that for a fixed radius, the luminosity of a star increases with the fourth power of the temperature; therefore, hotter stars are more luminous. That is exactly what happens along the main sequence, for although the radius varies by a relatively small amount along the main sequence, the luminosity variation is due mainly to a change in temperature.
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- The Life and Death of Stars , pp. 157 - 185Publisher: Cambridge University PressPrint publication year: 2013