PH109 Exploring the Universe, Test#4, Spring 2011

Please indicate the best answer to the following questions on the answer sheet provided.

1. Most of the mass of a galaxy is

a. contained in the massive O and B stars in the galaxy.

b. contained in the H I regions of the galaxy.

c. contained in the H II regions of the galaxy.

d. contained in the dark matter of the galaxy.

2. The mass of a single galaxy might be found by

a. the double galaxy method, b. the rotation curve method, c. the cluster method. d. any of these

3. For what type of object is the period-luminosity relation used for determining distances?

a. Algol variables, b. Cepheids, c. Cataclysmic variables, d. 21 centimeter radiation.

4. The two dwarf irregular companions of the Milky Way Galaxy are known as the

a. bi-polar nebular, b. M31 and M32, c. Happy and Sleepy, d. large and small Magellanic clouds

5. 21 cm radiation is produced by which element?

a. hydrogen, b. helium, c. carbon, d. iron

6. The oldest stars in the galaxy are found

a. in globular clusters in the halo, b. at the center of the galaxy

c. on the front rim of spiral arms, d. in the galactic disk

7. What is the name of the nearest large galaxy to our own

a. Milky Way, b. Andromeda, c. Orion, d. Cygnus

8. Hubble’s law states that:

a. putting telescopes in space will cost approximately ten times more

b. the recession of one galaxy must equal the precession of another

c. the faster a galaxy moves away from us the more massive it is

d. the faster a galaxy moves away from us the farther away it is

9. What type of galaxy is the Andromeda galaxy M31?

a) spiral, b) globular, c) elliptical, d) irregular

10. The location of our Sun in the galaxy is approximately

a) near the core, b) near the outer edge

c) about 2/3 of the way out to the edge, d) not currently determined

11. The radio emission from radio galaxies and quasars is due to

a) thermal emission, b) blackbody radiation, c) O and B stars, d) synchrotron radiation

12. What is hardest to explain about spiral arm structure

a) that they ever existed in the first place, b) why galaxies only have two of them

c) why they have sharp boundaries, d) how they maintain themselves

13. When Galaxies collide

a) their stars collide to form larger stars, b) both galaxies crumple into very dense systems

c) they simply perturb each other’s shape, d) no galaxies are left after the collision

14. Why is the energy source of active galaxies thought to be extremely compact?

a) Their energy is totally no stellar in origin.

b) Their spectra are like those produced by ordinary stars.

c) They vary on rapid time scales.

d) They can be seen clearly; we can see that the energy source is compact.

15. What causes Cepheid variables to vary in brightness?

a) they pulsate, b) eclipses,

c) changes in nuclear energy generation rate, d) obscuration by clouds of dust

16. Quasars were originally discovered as

a) strong radio sources identified with star-like images on photographs

b) variable sources of light

c) bright galaxies, and only later found to be radio sources

d) the only type of radio source within our galaxy

17. Which type of galaxy contains the least amount of interstellar material?

a) Ellipticals, b) spirals, c) barred spirals, d) irregulars

18. A primary difference between spiral and elliptical galaxies is

a) all ellipticals are more massive than spirals

b) ellipticals have more extensive interstellar media than spirals

c) star formation has ceased in ellipticals, but not in spirals

d) spirals have more stars than ellipticals

19. Why do the cores of spiral galaxies appear redder than the arms

a) because of reddening due to dust, b) because the stars are older

b) because the star s move so fast, d) because of black holes in the center

20. The distribution of galaxies in the universe

a) follows the same distribution as stars, b) arraigned on the surfaces of giant bubbles or voids

c) fairly uniform, d) has remained the same as it was during the big bang

21. Hubble’s law describes a relationship between a galaxy’s

a) size and brightness, b) number of stars and size, c) shape and age, d) redshift velocity and distance

22. Galaxies which show no structural features, but a smooth apparently three-dimensional luminosity, are called

a) boring, b) spirals, c) irregulars, d) ellipticals

23. Why is our galaxy in the shape of a disk

a) because it rotates

b) because it got sheered off during a galactic collision

c) the outer parts were torn away by the Magallenic clouds

d) the dark matter holds it in that formation

24. How was Hubble able to determine the distances of nearby galaxies?

a) by using radar

b) by measuring trigonometric parallaxes

c) by measuring the typical angular separations of stars in them

d) by observing Cepheid variables in them

25. Which of these objects are not found in the Galactic Halo?

a) RR Lyrae variables ,b) globular clusters,c) emission nebulae ,d) stars with comet-like orbits

26. In the formation of our Galaxy, the ______formed first.

a) galactic disk ,b) galactic center ,c) globular clusters, d) spiral arms

27. What good are 21 cm radio waves to galactic astronomers?

a) They cut through the dusty cocoons to let us watch star birth.

b) We can reflect them off the core of the Galaxy.

c) Their Doppler shifts let us map the motions and locations of spiral arms.

d) They bounce off stars like our Sun to let us precisely measure their distances.

28. Why are the supermassive giant ellipticals found at the centers of the rich galaxy clusters?

a) Most of the matter forming the cluster fell to the center at the beginning.

b) In the beginning, its mass attracted the smaller nearby galaxies to form the cluster.

c) The concentration of dark matter dictated this.

d) Such giants are the result of many mergers, cannibalizing smaller neighbors.

29. Based on galactic rotation curves and cluster dynamics, we think dark matter:

a) is a minor component of the entire mass of the universe.

b) is best detected from the x-rays it produces in the intergalactic medium.

c) will have no effect on the fate of the universe.

d) comprises over 90% of the entire mass of the universe.

30. Which of these astronomers first related speeds and distances for galaxies?

a) Harlow Shapley , b) Edwin Hubble , c) Vesto M. Slipher, d) William Herschel

31. The size of our galaxy is about

a) 3 light years, b) 120 thousand light years, c) one mega parsec, d) unknown at the present

32. In what part of the spectrum can astronomers observe the 21 cm radiation?

a) visible, b) infrared, c) radio, d) X-Ray

33. Where are globular clusters located in the galaxy?

a) in the nucleus, b) in the disk, c) in the spiral arms, d) in the halo

34. Quasars may be caused by

a) directly viewing jets of material from black holes, b) interacting galaxies

c) massive super-nova explosions, d) left over fragments of the big bang explosion

35. About how long does it take for the Sun to complete one trip around the galaxy?

a) 25 thousand years, b) 2.5 million years, c) 250 million years, d) 25 billion years

36. What was Klemperer’s dream about?

a) the Big Bang, b) dark mater, c) black holes, d) colliding galaxies

37. The object located at the center of our Galaxy is believed to be a ______.

a) a large cluster of stars, b) an emission nebulac) a black hole, d) a massive supernova

38. A rotation curve for a galaxy is a plot of

a) orbital speed versus distance from center, b) number of rotations versus time

c) orbital distance versus eccentricity, d) temperature versus luminosity

39. What type of galaxy is frequently found at the center of a rich cluster of galaxies?

a) elliptical, b) spiral, c) barred spiral, d) irregular

40. Irregular galaxies have ill defined shape because

a) they rotate too slow to form a disk, b) active star formation disrupts disk

c) too many black holes distort space time, d) recent collisions caused loss of shape