Phys_306_Exam

Physics 306 Exam 3

Please give clear, specific, and unambiguous answers.

Partial credit will be given on Questions 4, 6, and 7, but not on the short-answer questions.

For the short-answer questions, fill in the blank, circle the letter for the correct answer, etc., as indicated.

1. (4) Approximately how fast is a galaxy moving away from us if its red shift is 0.36? Here c represents the speed of light.

(a) 10% of c

(b) 20% of c

(d) 40% of c

(e) 50% of c

(f) 60% of c

(g) 70% of c

(h) 80% of c

(i) 90% of c

2. (4) Suppose a galaxy contains globular clusters that are about 3 seconds of arc in diameter, and that these clusters are known to be about 25 pc in diameter. Approximately how far away is this galaxy?

(a) 0.3 kpc

(b) 1.1 kpc

(d) 2.6 kpc

(e) 0.3 Mpc

(f) 1.1 Mpc

(g) 1.7 Mpc

(h) 2.6 Mpc

3. (4) If the RR Lyrae stars in a globular cluster have apparent magnitudes of 17, how far away is the cluster? Take the absolute magnitude of an RR Lyrae star to be +0.5, and give your answer in kiloparsecs.

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4. Describe how each of the following can be used to determine the distance of an astronomical object. You should be reasonably brief, but clear, complete, and specific.

(a) (4) Cepheid variables (including what they are).

(b) (4) Tully-Fisher relation (including what it is).

(d) (4) Type I supernovae (including what they are).

5. (4) In the standard model of particle physics,

(a) a proton consists of one up quark and two down quarks, and a neutron consists of two up quarks and one down quark, with the strong nuclear force carried by gluons

(b) a proton consists of two up quarks and one down quark, and a neutron consists of one up quark and two down quarks, with the strong nuclear force carried by gluons

(c) a proton consists of one up quark and two down quarks, and a neutron consists of two up quarks and one down quark, with the strong nuclear force carried by weak bosons

(d) a proton consists of two up quarks and one down quark, and a neutron consists of one up quark and two down quarks, with the strong nuclear force carried by weak bosons

(e) a proton consists of one up quark and two down quarks, and a neutron consists of two up quarks and one down quark, with the strong nuclear force carried by neutrinos.

6. What are the "four pillars" of big bang cosmology? I.e., what are the four fundamental observations in astronomy that demonstrate the universe began in a hot big bang?

(a) (2)

(b) (2)

(d) (2)

7. (6) In your own words, outline the standard history of the universe, starting with the point where gravity has already separated from the other three forces. (This standard picture includes both the standard cosmology of the relatively late universe, and the more speculative earlier description based on particle physics.) Be as specific as you can about what happened at , e.g., a few millionths of a second, one minute, and 300,000 years. Also indicate the future of the universe as based on very recent observations of distant supernovae.

8. (4) If we find a galaxy that is about the same size and mass as our Milky Way Galaxy, what approximate orbital velocity would a small satellite galaxy have if it orbited 40 kpc from the center of the larger galaxy? For reference, the sun has an orbital velocity of about 220 km/sec as it revolves in the Milky Way, and it is about 8.5 kpc from the center.

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9. (4) Infrared radiation from cool stars is observed at a wavelength of about 1500 nanometers. What is the approximate temperature of the stars emitting this radiation?

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10. A galaxy is 15 Mpc away from us and is observed to recede from us at 900 km/sec.

(a) (2) What effect is used to determine this recessional velocity?

(b) (2) What is the value of the Hubble constant?

(c) (2) Now assume that the universe is flat. (This means taking into account the deceleration due to gravity acting on matter, but neglecting the recently discovered effect of a cosmological constant.) What is the age of the universe in this picture, as inferred from the above value of the Hubble constant?

11. (4) The oldest stars in a galaxy are typically moving in

(a) well-defined parabolic trajectories outside the galactic disk

(b) well-defined elliptic orbits outside the galactic disk

(d) well-defined elliptic orbits within the galactic disk

(e) parabolic trajectories outside the galactic disk which vary erratically with time

(f) elliptic trajectories outside the galactic disk which vary erratically with time

(g) parabolic trajectories within the galactic disk which vary erratically with time

(h) elliptic trajectories within the galactic disk which vary erratically with time

12. (4) Which of the following are thought to be closely associated with active galactic nuclei? Circle all correct answers.

(a) BL Lac objects

(b) RR Lyrae stars

(d) pulsars

(e) quasars

(f) jets

(g) accretion disks

(h) Type I supernovae

(i) Seyfert galaxies

13. (4) The spiral arms of a galaxy can be clearly seen because

(a) they contain large quantities of gas

(b) they contain large quantities of dust

(d) they contain recently created bright stars

(e) they contain high concentrations of old stars

(f) they are the natural accumulation points for galactic matter

14. (4) Quasars occur most commonly at red shifts of about

(a) 4

(b) 2

(d) 0.35

(e) 0.25

(f) 0.15

15. (4) The relative variations in the cosmic microwave background radiation, from one point to another across the night sky, are about

(a) 1 part in 10

(b) 1 part in 100

(d) 1 part in 10,000

(e) 1 part in 100,000

(f) 1 part in 1,000,000

16. (4) One of the strongest pieces of evidence for dark matter is provided by the velocity curves for matter rotating well outside nearly all the visible mass of the galaxy. According to Newton's law of gravity (or Kepler's law) the velocity v should vary with the distance r from the center of rotation as

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17. (4) If life on earth began about 3.5 billion years ago, and the solar system revolves around the galaxy once every 240 million years, how many revolutions has the earth made since its life began?

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18. (4) Indicate whether each of the following contains mostly blue stars, yellow stars, or the most ancient stars. (Give the most precise answer in each case.)

(a) globular clusters ________________________________

(b) outer spiral arms _________________________________

19. (4) According to the best current estimates based on the oldest stars and the expansion rate of the universe, the age of the universe is about

(a) 6-8 billion years

(b) 10-12 billion years

(d) 17-19 billion years

(e) 20-22 billion years

(f) 23-25 billion years.

20. (4) The current temperature of the cosmic microwave background radiation is about

(a) 0.3 K

(b) 3K

(d) 300 K

(e) 3000 K

(f) 30,000 K

(g) 300,000 K.