A100 Week 6

1. Choose the statement that is inconsistent with the theory that the Milky Way began with the collapse of a spherical gas cloud that later flattened into a disk?
       a. We observe fewer white dwarf stars in the disk than there would be for an 11-billion year old disk.
       b. The globular cluster stars in the galaxy halo are all old.
       c. The metals in the globular clusters is about one tenth the Sun's value.
       d. Nonsense - all of the above observations are consistent with the standard collapse-from-a-cloud theory.
   

2. How did Harlow Shapley determine the location of the center of our galaxy?
       a. The geometric center of the more massive stars in the spiral arms.
       b. Globular clusters distributed in the galactic halo.
       c. He found a bright, massive object in the core.
       d. Cepheid variables near the galactic core.
   

3. Which of the following arguments supports the idea that large elliptical galaxies formed by mergers of smaller galaxies?
       a. Big ellipticals lack gas and dust, and galactic collisions can allow central supermassive black holes to consume all pre-existing gas and dust.
       b. Big ellipticals are generally found near the center of rich galaxy clusters containing many individual galaxies.
       c. Ellipticals have lots of gas and dust, and collisions can spur star formation that also forms gas and dust.
       d. All the above arguments support the idea of galaxy mergers forming big elliptical galaxies.
   

4. Which of these describes the total mass of our galaxy?
       a. Several thousand times the mass of the Sun.
       b. Several million times the mass of the Sun.
       c. Several billion times the mass of the Sun.
       d. Several hundred billion times the mass of the Sun.
   

5. One piece of evidence for a 4-million solar mass black hole at the center of our galaxy is from which of the following observation?
       a. Distorted background stars near the core.
       b. Short duration X-ray bursts from an accretion disk: the time implies a compact source.
       c. A star passing within a light-day of galactic center at more than 100% of light speed, as measured at infrared wavelengths.
       d. The orbit of Sun-like stars orbiting within a few light-years of galactic center, as measured by optical telescopes through a hydrogen-alpha filter (656 nm).
   

6. Where is the best place to look for the oldest stars in the Milky Way?
       a. Evenly distributed.
       b. In the spiral arms.
       c. In the center and in the halo.
       d. In the halo and the spiral arms.
   

7. Which of the following is a list of distance indicators (standard candles) used by astronomers?
       a. emission and reflection nebulae in molecular clouds, nova explosions on white dwarfs, main-sequence stars
       b. lyra variable stars, cepheid variable stars, white-dwarf supernovae
       c. white dwarf stars, Cepheid variables, black hole binary systems, massive star supernovae
       d. emission by super-massive black holes located at the center of nearly every large galaxy, spinning spiral galaxies
   

8. Type Ia supernovae (white dwarf detonation) are useful for measuring distances because...
       a. the periodicity of the light curve is tightly correlated with the peak luminosity.
       b. the explosion is recurrent, and the time between explosions correlates with the peak luminosity.
       c. the exploding star has about the same mass and composition in each case, it is bright, and the light curve is always the same.
       d. the rotation rate of the object is easily measured and correlates with the peak luminosity.
   

9. Which of the following is supporting evidence for the existence of dark matter?
       a. the relatively high-speed motion of stars in the halo
       b. the shape of the rotation curve for elliptical galaxies
       c. hot, diffuse hydrogen/helium gas observed (via X-rays) in clusters of galaxies
       d. all of the above
   

10. What type of stars did Shapley actually use to measure distances to the globular clusters in our galaxy (as opposed to the ones he thought he used)?
        a. Wolf-Rayet
        b. T-Tauri
        c. Cepheid variables
        d. RR Lyrae variables
    

11. Which of the following is NOT a result of stellar evolution in galaxies over long time periods, in the absence of galaxy merger?
        a. Increasing hydrogen within the interstellar medium.
        b. Decreasing rate of star formation with time.
        c. Increasing number of white dwarfs, neutron stars, and stellar black holes.
        d. Decreasing hydrogen within the interstellar medium.
    

12. Where within our galaxy is our solar system?
        a. In the disc of the Milky Way Galaxy and about 30,000 light years from the center.
        b. Near the outer edge of the disc, about 90,000 light years from the core.
        c. Above the disc the Milky Way Galaxy and about 10,000 light years from the center.
        d. At the outer edge of the the Milky Way galactic bulge, about 10,000 light years from the center, in the plane of the disc.
    

13. How did Edwin Hubble figure out that the Andromeda Galaxy is outside the Milky Way?
        a. He found no Cepheid variable stars in the Milky Way which proved that Andromeda had to be another galaxy.
        b. He measured the geometric parallax of a Cepheid Variable in Andromeda and showed that it was far outside the Milky Way Galaxy.
        c. He found that Cepheids are a type of luminous galaxy and Andromeda is an example.
        d. He calculated the distance from the measurment of the period-luminosity correlation for Cepheid variable stars.
    

14. Why are sun-like (one solar mass) stars good tracers for the locations of the spiral arms in the Milky Way galaxy?
        a. Sun-like stars form in spiral arms and remain in the spiral arms near to the location where they originate.
        b. Sun-like stars form in spiral arms and move along the same spiral toward the center of the galaxy.
        c. Sun-like stars can form anywhere in the disk, but migrate gravitationally to the nearest spiral arm, where they then spend the rest of their life.
        d. Sun-like stars are acutally not good spiral arm tracers in spiral galaxies.
    

15. If another galaxy has a star that is a similar distance from its center as our sun is in our galaxy (30,000 lightyears), and we measure its orbital speed to be similar to that of our sun (125 km/s), how does the mass of that galaxy compare with the mass of our own galaxy?
        a. The galaxy's mass (inside the star's orbit) is more than that of our Milky Way galaxy.
        b. The galaxy's mass (inside the star's orbit)  is about the same as that of our Milky Way galaxy.
        c. The galaxy's mass (inside the star's orbit) is less than that of our Milky Way galaxy.
        d. Without more information about the mass of the orbiting star, we cannot answer the question.
    

16. Suppose you are in an alternate Universe, and you observe that distant galaxy clusters exhibit blue-shifts proportional to distance. What would you conclude?
        a. That the Universe is expanding and will continue to expand into the future.
        b. That the Universe is in a steady state, with no average expansion or contraction.
        c. That the Universe is contracting and that it will come together at some point in the future.
        d. That intergalactic dust caused the apparent blue-shift because of preferential scattering of blue light by dust particles.
    

17. What sort of things do we observe in the halo of our galaxy?
        a. gas and dust and emission and reflection nebulae
        b. open clusters full of newly born stars
        c. globular clusters containing mostly very old stars
        d. lots of very hot blue stars
    

18. Who discovered the relationship between the fluctuating period of variable stars, and their intrinsic brightness?
        a. Henrietta Leavitt
        b. Harlow Shapley
        c. Edwin Hubble
        d. Annie Cannon
    

19. How is 21cm wavelength light useful to astronomers?
        a. It lets astronomers learn about the process of star formation by mapping the distribution of molecular gas.
        b. It lets astronomers use distant stars in the Galaxy's halo because these signals penetrate the dust in the Galaxy's disk.
        c. It lets astronomers map the large-scale motion and distribution of atomic hydrogen in the Milky Way.
        d. It lets astronomers see through molecular gas into the Milky Way's black holes.
    

20. Gravitational interactions between two or more galaxies can result in...
        a. compression of gas/dust clouds and rampant star formation.
        b. a merger or severe change of shape for the galaxies entering the interaction.
        c. the stripping of gas and dust from one of the galaxies, resulting in the shut-down of future star formation and long 'tails' of gas.
        d. all of the above.