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Astronomy 1020-H Stellar Astronomy Spring_2014 Day-31

Astronomy 1020-H Stellar Astronomy Spring_2014 Day-31. Course Announcements. Exam-4 Monday Apr. 14; Ch. 16, 17, 18(?) SW ch. 16 due Fri 4/11; Ch. 17, 18 – Mon 4/14 1 st Quarter Observing – Mon. 4/7 @8:30pm Archwood parking lot OR atrium of SSB Rain, shine, sleet, snow … it’s on

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Astronomy 1020-H Stellar Astronomy Spring_2014 Day-31

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  1. Astronomy 1020-H Stellar Astronomy Spring_2014 Day-31

  2. Course Announcements • Exam-4 Monday Apr. 14; Ch. 16, 17, 18(?) • SW ch. 16 due Fri 4/11; Ch. 17, 18 – Mon 4/14 • 1st Quarter Observing – Mon. 4/7 @8:30pm • Archwood parking lot OR atrium of SSB • Rain, shine, sleet, snow … it’s on • Lunar Eclipse … Mon-Tues. 4/14-15/2014 • IF CLEAR, we’ll be at the observatory from about 0100-ish on. • Dark night, 4/23/2014 (Wed.) weather dependent.

  3. Star Formation & LifetimesLecture Tutorial pg. 119 • Work with a partner! • Read the instructions and questions carefully. • Discuss the concepts and your answers with one another. Take time to understand it now!!!! • Come to a consensus answer you both agree on and write complete thoughts into your LT. • If you get stuck or are not sure of your answer, ask another group.

  4. PROCESS OF SCIENCE • Type Ia Supernovae over time have become very useful. • This could only happen after more scientists with greater technology analyzed their properties and realized connections.

  5. High-mass stars live different, faster lives. • On the main sequence, energy is generated from the carbon-nitrogen-oxygen (CNO) cycle, with carbon as a catalyst:12C + 4 1H + 2  e = 12C + 4He + gamma rays + neutrinos.

  6. High-mass stars have convection to mix H in the core. • Increases the mass available for fusion. • Once H is exhausted from the core, the star leaves the main sequence and expands and cools.

  7. Move right on the H-R diagram: supergiants. • Ignite He in a nondegenerate core, unlike low-mass stars. • With rising central temperatures, heavier elements (C, Ne, etc.) fuse, generating energy.

  8. After the carbon runs out, heavier elements start fusing

  9. The more massive the star, the heavier the elements that can fuse. • As temperature rises and core fuel is used up, heavier and heavier elements will fuse, up until iron. • The fusion shells build up like the layers of an onion.

  10. As high-mass stars expand and cool, they can pass through the instability strip on the HR diagram. • Here, the combination of temperature and luminosity results in the stars’ pulsation.

  11. These pulsating variable stars are extremely important for determining distances. • Specifically, they have a period-luminosity relationship.

  12. Cepheid variables: • High-mass stars becoming supergiants. • Periods from one to 100 days. • More luminous stars have longer periods. • RR Lyrae variables: • Low-mass stars on the horizontal branch. • Less luminous than Cepheid variables.

  13. CONNECTIONS 17.1 • Intermediate-mass stars have masses between 3 and 8 M. • Start off evolving as high-mass stars, but finish as low-mass stars do, as white dwarfs. • Very massive stars may shed some mass due to instabilities and go through a luminous blue variable (LBV) phase.

  14. Concept Quiz—Cepheid Variables Why are Cepheid variable stars so important? • We can know their luminosities. • They produce pulsars. • They are about to explode as supernovae. • They generate most heavy elements.

  15. Once an iron core starts to form, the end comes quickly

  16. Fusion of iron or more massive elements requires energy—the star cannot use them for fuel. • Once the star has an iron core, it cannot generate more energy. • Fusion stops, and the core collapses.

  17. Photodisintegration doesn’t relieve the electron degeneracy pressure Things get so crowded the electrons are squeezed into the nucleus where they combine with protons to make neutrons in a process called Reverse Beta Decay

  18. Each stage of burning is progressively shorter. • Example: Si burning only lasts for a few days. • Why? Huge production of neutrinos, which carry away energy neutrino cooling. • The star cannot access the huge amount of energy produced in neutrinos.

  19. Each type of fusion takes higher temperatures and last less time

  20. MATH TOOLS 17.1 • The net energy released by a nuclear reaction is the difference between the binding energy of the products and the binding energy of the reactants. • For the triple-alpha process: • For the fusion of iron, the binding energy of the products is less than that of the reactants, so the net energy is negative.

  21. Core collapses, central temperature rises. • Photodisintegration, neutrino cooling reduces pressure, collapse accelerates. • Electron degeneracy cannot help.

  22. Collapses until it reaches nuclear densities. • At these high densities, nuclear forces repel atoms. • Core stops, bounces back, driving a shock wave through star.

  23. Shock wave takes a mere few hours to rip through the star. • Outer layers blow off in tremendous explosion (Type II supernova). • Dense core remains.

  24. Light energy emitted is about 1 billion Suns. • Kinetic energy of blown-off outer parts: 100x. • This kinetic energy is transferred to the interstellar medium (ISM), heating it. • Neutrinos carry off an energy of 100 times larger still!

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