Lecture 29. Black Holes, Relativity, & Galaxies

Lecture 29. Black Holes, Relativity, & Galaxies

A. Class Business

  1. Reading for Wed.:
    1. HANDOUT
    2. Secs. 24.4, 27.4
    3. box, p.495

  2. turn in OUT-OF-CLASS ACTIVITY papers TODAY, 8/2, by 3:00 --
      if not in class, then in my box in the Physics Dept. office upstairs

  3. Homework 5. due at end of this class!


B. Neutron Stars & Pulsars

  • Pulsars are NEUTRON STARS whose MAGNETIC POLES rotate past us -- "lighthouse" model














    C. Black Holes










    D. Galaxies -- Our Own, and Others

    1. the Milky Way -- our galaxy

      • STRUCTURE:
        • a) flat disk shape -- most matter in DISK, some in HALO
        • b) SPIRAL arms (with BAR?) -- our Sun is on ORION "SPUR"
        • c) NUCLEAR BULGE in center (toward Sagittarius)
            -- home of a SUPERMASSIVE BLACK HOLE?

          In left image, different symbols denote locations of stars at different times. In right image, stars marked with larger symbols have larger estimated velocities.

          Q: What do we call the changes in position of the stars in the left image? __________________






      • FACTOIDS:
        • a) diameter -- 100,000 ly
        • b) thickness -- 1,000 ly
        • c) number of stars -- 1011

      • Orbital Speed vs. Distance from Nucleus
        • Q: Do stars farther from the nucleus orbit faster or slower than closer stars? ________________
        • Q: Whose law predicts this? _______________

        As we'll see Wednesday, this isn't the whole story!


    2. Other Galaxies










    3. HUBBLE'S LAW

      Q: When we look at faraway galaxies, their spectral lines are red shifted to the red. Why?

        A: Their radial velocity away from us Doppler shifts their emissions!

      • The FARTHER an object is, the more its lines are redshifted, meaning it's moving away FASTER.
          -- relation is LINEAR: TWICE as far means TWICE as fast!

      • EXPANSION has NO CENTER: everything moves away from everything!

      • OBJECTS are NOT expanding, only the space between them!
          Q: WHY don't we expand, too? ________________________

        Q: Figure 25.17 (p.514) is misleading. HOW SO?

          __________________________________________________





    E. General Relativity

    Recall that our Earth orbits the Sun, which orbits the Milky Way's center, which orbits the Local Group's center, which orbits the virgo Supercluster's center.

    Q: How come we don't feel the fact that we're moving so fast?*