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Part 15: Stellar birth and death, nucleosynthesis, and thermodynamics.


These short videos were created in August 2007 by Dr. Christopher D. Impey, Professor of Astronomy at the University of Arizona, for his students. They cover a broad range of terms, concepts, and princples in astronomy and astrobiology. Dr. Impey is a University Distinguished Professor and Deputy Head of the Astonomy Department. All videos are intended solely for educational purposes and are licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. The full list of collections follows below:

01. Fundamentals of Science and Astronomy
02. Ancient Astronomy and Celestial Phenomena
03. Concepts and History of Astronomy and Physics
04. Chemistry and Physics
05. Quantum Theory and Radiation
06. Optics and Quantum Theory
07. Geology and Physics
08. Solar Neighborhood and Space Exploration
09. Outer Planets and Planetary Atmospheres
10. The Solar System
11. Interplanetary Bodies
12. Formation and Nature of Planetary Systems
13. Particle Physics and the Sun
14. Stars 1
15. Stars 2
16. Stars 3
17. Galactic Mass Distribtuion and Galaxy Structure
18. Galaxies
19. Galaxies 2
20. Galaxy Interaction and Motion
21. Deep Space and High-Energy Phenomena
22. The Big Bang, Inflation, and General Cosmology
23. The Big Bang, Inflation, and General Cosmology 2
24. Chemistry and Context for Life
25. Early Earth and Life Processes
26. Life on Earth
27. Life in the Universe
28. Interstellar Travel, SETI, and the Rarity of Life
29. Prospects of Nonhuman Intelligences

15. Stars 2 University of Arizona

    • Wetenschap

Part 15: Stellar birth and death, nucleosynthesis, and thermodynamics.


These short videos were created in August 2007 by Dr. Christopher D. Impey, Professor of Astronomy at the University of Arizona, for his students. They cover a broad range of terms, concepts, and princples in astronomy and astrobiology. Dr. Impey is a University Distinguished Professor and Deputy Head of the Astonomy Department. All videos are intended solely for educational purposes and are licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. The full list of collections follows below:

01. Fundamentals of Science and Astronomy
02. Ancient Astronomy and Celestial Phenomena
03. Concepts and History of Astronomy and Physics
04. Chemistry and Physics
05. Quantum Theory and Radiation
06. Optics and Quantum Theory
07. Geology and Physics
08. Solar Neighborhood and Space Exploration
09. Outer Planets and Planetary Atmospheres
10. The Solar System
11. Interplanetary Bodies
12. Formation and Nature of Planetary Systems
13. Particle Physics and the Sun
14. Stars 1
15. Stars 2
16. Stars 3
17. Galactic Mass Distribtuion and Galaxy Structure
18. Galaxies
19. Galaxies 2
20. Galaxy Interaction and Motion
21. Deep Space and High-Energy Phenomena
22. The Big Bang, Inflation, and General Cosmology
23. The Big Bang, Inflation, and General Cosmology 2
24. Chemistry and Context for Life
25. Early Earth and Life Processes
26. Life on Earth
27. Life in the Universe
28. Interstellar Travel, SETI, and the Rarity of Life
29. Prospects of Nonhuman Intelligences

    • video
    Mass and Stellar Evolution

    Mass and Stellar Evolution

    Transcript: Mass is the fundamental quantity that controls stellar evolution. The main sequence on an HR diagram is a correlation between the properties of luminosity and effective temperature. The main sequence runs from high luminosity hot stars down to low luminosity cool stars, but the underlying variable on the main sequence is the mass of the star. High luminosity hot stars are high mass and low luminosity cool stars are low mass. The principles of stellar evolution were first worked out by the English theorist Arthur Eddington in the 1920s. He used the idea of pressure force balancing the gravity inward force in a star to deduce the way that stars evolved. This hydrostatic equilibrium that applies at every point within a star creates a stable situation where the rate of evolution is governed by mass.

    • 1 min.
    • video
    Mass Limits for Stars

    Mass Limits for Stars

    Transcript: A star is a ball of gas held together by gravity where the temperature in the interior is sufficient to release energy by fusion reactions. The Sun is a typical star, but what sets the mass range of stars? Is it possible for example to have a star a thousand times less massive than the Sun or a thousand times more massive? The answer is no. Stellar physics dictates a particular range in which stars can exist. It spans a factor of about a thousand. Less than 0.08 times the mass of the Sun, that is eight percent of the mass of the Sun, the temperature in the interior never achieves the ten million degrees Kelvin needed to cause the fusion reaction of hydrogen to helium. Thus an object less than eight percent of the mass of the Sun is not a true star. It may indeed be a hot ball of gas, but it’s not releasing energy by fusion. Above about a hundred times the mass of the Sun, a gas cloud that collapses and might form a star collapses with such violence that it blows itself apart and never sets up a stable configuration. Thus there are natural limits to the mass ranges of stars.

    • 1 min.
    • video
    Properties of Main Sequence Stars

    Properties of Main Sequence Stars

    Transcript: Main sequence stars have several basic properties. All main sequence stars are converting hydrogen to helium by the fusion process, and that’s responsible for the energy release and the radiation that leaves the stars. Main sequence stars are all stable with their internal structure governed by the principle of hydrostatic equilibrium. The most massive main sequence stars are more luminous, physically larger, and have hotter photospheres than low mass main sequence stars. Main sequence stars come in the mass range from about a tenth the mass of the Sun to about a hundred times the mass of the Sun, but the most abundant main sequence stars have around the mass of the Sun or lower.

    • 50 sec.
    • video
    Types of Main Sequence Stars

    Types of Main Sequence Stars

    Transcript: Main sequence stars are classified according to the system of spectral types developed almost a hundred years ago. Going from the hottest to the coolest stars there are O type main sequence stars whose mass is about fifty times that of the Sun, radius about twenty times, a temperature of forty thousand degrees, and a luminosity a million times that of the Sun. B stars have masses twenty times that of the Sun and radii seven times that, photospheres are thirty thousand Kelvin and the luminosity is about twenty thousand times that of the Sun. A stars masses three times that of the Sun and radius three times, ten thousand degree atmospheres, and eighty times the Sun’s luminosity. F stars mass of 1.7 times the Sun’s mass and radius 1.4 times, seventy-five hundred degree Kelvin for the photosphere, and six times the luminosity of the Sun. G stars, similar to the Sun, 1.1 times the mass and the radius, six thousand degree atmospheres, and 1.3 times the Sun’s luminosity. K stars 0.8 times the mass of the Sun and the same factor for the radius, five thousand degree atmospheres, and 0.4 solar luminosities. And the coolest M stars about a half the mass of the Sun, 0.6 times the solar radius, a photosphere of thirty-five hundred Kelvin and luminosity of 0.03 times the Sun’s luminosity.

    • 1 min.
    • video
    The Sun as a Star

    The Sun as a Star

    Transcript: The Sun is a typical main sequence star by which astronomers mean that the Suns properties lie in the middle of the range of stellar properties on the main sequence. It’s intermediate in mass, in size, in temperature, and luminosity compared to the most and least massive main sequence stars. The Sun has a spectral type G2 which gives it a photosphere temperature of fifty-seven hundred Kelvin. Spectral types O, B, A, F, G, K, and M are subdivided on a decimal scale running from O1 to O8 to O9 to B0, B1, etcetera. The Sun as a G2 star is a little cooler than a G0 star. The Sun is typical in most properties, but most stars are less massive than the Sun and the very highest mass main sequence stars are extremely rare.

    • 59 sec.
    • video
    Main Sequence Lifetime

    Main Sequence Lifetime

    Transcript: The steep relationship between mass and luminosity for main sequence stars has an important consequence for the lifetime of the stars. Consider a star that’s a tenth the mass of the Sun. In round numbers the luminosity is ten to the minus four times the luminosity of the Sun. Thus the size of the fuel reservoir is ten times smaller, but the rate of evolution is ten thousand times smaller. This means the star will last about a thousand times longer than the Sun. Instead of a total main sequence life of ten to the ten years, we have a total main sequence life of ten to the thirteen or ten trillion years. Compare it to the other end of the main sequence. A star of a hundred times the mass of the Sun in round numbers has a luminosity a million times that of the Sun. Although the fuel reservoir is a hundred times larger than the Sun, the rate of burning the fuel is a million times larger which means the star lasts ten thousand times less long than the Sun. Instead of a main sequence lifetime of ten billion years, we have a main sequence lifetime of roughly a million years.

    • 1 min.

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