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Astronomy 103 Final review session

Astronomy 103 Final review session. Dec 13 2007. What we’ll talk about. Topics covered since last exam Strategies for studying for the final Date and location of the exam. Topics. Since the last exam, we have essentially covered three subject areas Stars and their evolution Galaxies

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Astronomy 103 Final review session

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  1. Astronomy 103Final review session Dec 13 2007

  2. What we’ll talk about • Topics covered since last exam • Strategies for studying for the final • Date and location of the exam

  3. Topics • Since the last exam, we have essentially covered three subject areas • Stars and their evolution • Galaxies • Cosmology So lets remind ourselves about each…

  4. HR Diagram • Useful for exploring properties of stars • Can tell you about stellar evolution • Compares temperature in K on x-axis to Luminosity in solar units on y-axis • Remember that temperature runs from hot to cool! • Moving from lower right to upper left, stars increase in radius • Moving from upper right to lower left, stars decrease in mass

  5. Star formation • Stars form from giant clouds of gas which collapse under gravity • Eventually, protostars form • Once hot enough, hydrogen fusion can begin • Contraction halts once star reached hydrostatic equilibrium - balance of gas pressure and gravity • At this point, star has reached the Main sequence

  6. Main sequence stars Main sequence

  7. Main Sequence stars cont. • A useful definition of a main sequence star is • A mass of gas burning hydrogen in helium in its core • In hydrostatic equilibrium, and so therefore stable • The most important factors in determining the future evolution and fate of a star are • Its mass (the available fuel) • Its luminosity (the rate of fuel consumption)

  8. Mass-Luminosity relationship L = M3.5

  9. Main sequence lifetime • Stars live for different lengths of time depending on their mass - the most massive stars live for the shortest amount of time since they use up their available fuel most quickly • tMS = M/L • Substituting in the mass-luminosity relation, we find that tMS = 1/M2.5

  10. Stars are like cars…. • Massive stars have higher luminosities, so burn their fuel more quickly • Low mass stars have low luminosities and so burn their fuel more slowly • Compare to gas mileage of cars!

  11. Stellar Endpoints Initial mass remnant composition <0.5 Msol white dwarf helium 0.5 to 4 Msol white dwarf carbon/oxygen 4 to 8 Msol white dwarf oxygen/neon/magnesium 8 to 25 Msol neutron star neutrons >25 Msol black hole ? (>50 Msol neutron star? neutrons)

  12. Supernovae • End point for massive stars, leaving behind neutron star (pulsar) or black hole • Also end point for white dwarfs in binaries which grow in mass via accretion • Very energetic stellar explosion • Seeds elements into the interstellar medium • Can be used as a standard candle since luminosity known • Can outshine host galaxy for a short time

  13. Galaxies • Large gravitationally bound systems of stars • Contain billions of stars • Like stars, come in different masses and luminosities • Three types - spiral, elliptical and irregular • Galaxies are the basic building blocks of the universe

  14. Quasars and AGN • Many galaxies host supermassive black holes in their centers • Black hole mass many millions of solar masses • Quasars are galaxies where the active galactic nuclei is detected in the radio • In optical, these looked somewhat like stars, hence “Quasi-stellar radio sources” • Now can resolve host galaxies • More common in earlier stages of universe

  15. Expansion of universe • Edwin Hubble observed that galaxies are all moving away from us • We now know that this is due to the expansion of the universe • Hubble’s Law related recession velocity and distance V = H0d

  16. Age of universe • Look at the board!

  17. Big Bang • Universe started as a singularity of infinite density and infinite temperature • Everything began at the big bang - time, space and the laws of physics • Universe has been expanding and cooling ever since • Primordial elements which first galaxies and stars formed from were also produced in big bang - hydrogen, helium, lithium

  18. Cosmic microwave background • Afterglow of big bang - first light free to travel through universe unimpeded by matter • With expansion of universe, wavelength of this light has been stretched out • Longer wavelength - cooler temperature (Wiens Law) • See structures in big bang - initial density fluctuations which allowed structure to form in universe

  19. Cumulative material • Look at the board again! • Law of gravity • Stefan Boltzmann Law • Wiens Law • Inverse square law of light and standard candle • Energy of photon • The sun!

  20. How to study! • Look at your notes of what the professor discussed in class • Use practice questions to guide you to important facts and concepts • Use your notes from discussion • Use the powerpoint slides to guide your reading • Ask questions! Either of me, the professor or your classmates • Be aware of older concepts revisited in newer material

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