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The Powerhouse at the Center of the Sun

Explore the extraordinary luminosity of the Sun, analyzing its energy source and lifetime using equations. Discover the limitations of chemical reactions and the immense power of nuclear fusion in stars. Learn about nuclear reactions in stellar interiors and the mass-energy equivalence crucial for star fuel. Gain insights into the structure and power generation of main sequence stars, including methods to determine star masses.

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The Powerhouse at the Center of the Sun

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  1. The Powerhouse at the Center of the Sun

  2. The interior of the Sun is a region of extreme physical conditions

  3. Next topic: what is the luminosity of the Sun telling us? • Luminosity = 3.847X1026 Watts • What fuel cycle could provide this? • What fuel cycle could provide this for the lifetime of the Sun?

  4. Say it with equations! (easy ones) • Luminosity = power =energy/time • Energy=powerXtime (Watts X seconds = Joules) • Time=energy/power Let’s see how long we could keep the Sun shining with a known, powerful energy source

  5. Coal • Coal runs civilization • Energy content: 24 MegaJoules/kilogram= • 2.4X107 Joules/kg • If the Sun were made of coal, how long could it “burn”, providing its current power or luminosity?

  6. Power and the Sun • Mass of Sun = 2X1030 kilograms • Total energy content of “coal Sun”=(2X1030)X(2.4X107) =4.8X1037 Joules • Time the Sun could “keep this up” = energy/luminosity =4.8X1037/3.8X1026=1.3X1011 seconds • Is this a lot or a little????

  7. A strong conclusion: energy drawn from coal burning, or any other chemical reaction, is grossly inadequate to power the Sun over geological timescales

  8. Some vastly more powerful energy source (than chemical reactions) must be occurring in the Sun and stars

  9. A microscopic view of chemical reactions: interactions of the electron cloud

  10. Nuclear reactions: interactions among the nuclei (Figure 17.2)

  11. Nuclear Reactions in Stellar Interiors H + H 2H + e+ + nu H + 2H 3He + gamma 3He + 3He 4He + H + H Net effect: 4H 4He Question: why does this occur exclusively in the core of a star? Demo

  12. A small mass difference between Hydrogen and Helium • 4 Hydrogen atoms: 6.693E-27 kg • 1 Helium atom: 6.645E-27 kg • Difference = 0.048E-27 kg • Difference = 0.7 percent Why is this small difference important?

  13. The Einstein Energy-Mass equivalence relation E=mc2 c=speed of light You get a lot of bang for the buck: 6.3E+14 J/kg

  14. Stars have a lot of fuel in the form of hydrogen These abundances Are characteristic of the Solar photosphere, and Nearly all other stars

  15. The Power Source of Main Sequence Stars MS stars fuse hydrogen into helium, releasing prodigious amounts of energy in the process. Their fuel source is the matter of which they are made

  16. The Structure of Main Sequence Stars The Powerhouse

  17. How can we tell if this is right? Detect neutrinos emitted from the center of the Sun.

  18. The Neutrino Sun: A View into the Solar Interior

  19. Nuclear reactions explain a lot about the Sun, but what is going on on the rest of the Main Sequence?

  20. The fuel for a main sequence star is its own mass in the form of hydrogen. The total amount of fuel is proportional to the total mass of the star. What are the masses of stars?

  21. How We Determine Masses of Stars Method:observation of binary stars (double stars)

  22. Binary stars are numerous (e.g. Sirius)

  23. We can see orbital motion of Sirius B around Sirius A

  24. Masses of stars determine the gravitational force, and thus the acceleration of the stars

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