Fraknoi Chapter 25 The Milky Way Galaxy Complete Test Bank

Astronomy by Fraknoi, Morrison, and Wolff

Multiple Choice Questions for Chapter 25:

The Milky Way Galaxy

by Andrew Fraknoi

Section 25.1: The Architecture of the Galaxy

1. William Herschel thought that the Sun and Earth were roughly at the center of the great grouping of stars we call the Milky Way. Today we know this is not the case. What was a key reason that Herschel did not realize our true position in the Milky Way?

a. he did not have a telescope, and most stars are too far away to see without a telescope

b. his telescope was only able to show him objects inside the solar system, and not objects in the Galaxy

c. the dust that extends throughout the disk of the Galaxy only allowed Herschel to see the small part of the Milky Way that surrounds us

d. there are so many black holes in the Galaxy, that they absorb a substantial part of the light from distant objects; we needed x-ray astronomy to see to more distant regions

e. Herschel shared with ancient people the firm religious belief that we must be the center of everything

2. The scientist who made the first telescopic survey of the Milky Way and discovered that it is composed of a huge number of individual stars was

a. Isaac Newton

b. Galileo Galilei

c. Edwin Hubble

d. Harlow Shapley

e. Jill Tarter

3. What objects did Harlow Shapley use as "signposts" to figure out the extent of the Milky Way Galaxy and the location of its center?

a. thick clouds of cold hydrogen giving off 21-cm radiation

b. globular clusters

c. HII regions

d. dust clouds

e. big arches advertising "billions and billions sold"

4. What have we learned from the work of Harlow Shapley and others about the location of the Sun in the Milky Way Galaxy?

a. we are almost exactly in the center of a giant flat pinwheel

b. we are very close the edge of the visible disk of the Galaxy, more than 50,000 LY from the center

c. we are high above the disk of the Galaxy, about as far away as the most distant globular cluster

d. we are in the disk of the Galaxy, about 3/5 of the way from the center

e. you can't fool me; because of all the dust, astronomers still have no idea where our Sun is located in the Milky Way Galaxy

5. Astronomers today know a lot about the size and shape of the Milky Way Galaxy. Which of the following common objects most resembles the shape of our Galaxy?

a. a beach ball

b. a flag, fluttering in the breeze

c. a CD or DVD

d. a cake

e. a glazed donut

6. The central region of our Galaxy is not as flat as its main disk of stars. Which of the following has roughly the same shape as our central region of stars?

a. a peanut

b. a tennis ball

c. a cube

d. a long piece of string

e. actually, no one knows the shape of our central region because of all the dust in the Galaxy

7. Astronomers now know that surrounding the main body of our Galaxy (which our various kinds of telescopes have shown to us) and our fainter halo of stars there is

a. only the empty space that lies between galaxies

b. a series of hundreds and hundreds of nearby small galaxies, held in place by the Milky Way’s gravity

c. an invisible halo made of what astronomers are calling “dark matter”

d. a set of huge clouds with many interesting molecules (like alcohol, carbon monoxide, and ammonia) in them

e. a pair of long, bright jets of materials produced by a massive black hole and its accretion disk

8. Which of the following statements about the nuclear bulge of our Galaxy is FALSE?

a. it is significantly thicker than the disk of the Galaxy

b. it typically consists of older stars

c. it is difficult for us to see with visible light because of cosmic dust

d. the best way to learn more about it is to observe higher energy radiation, such as ultraviolet and x-rays

e. there is evidence that it is not exactly spherical, but elongated

Section 25.2: Spiral Structure

9. An astronomer needs to measure the distance to a globular cluster of stars that is part of the Milky Way Galaxy. What method should she try to use to find the distance?

a. measure the parallax of the cluster

b. count the number of O and B type stars in the cluster

c. look for flickering x-rays coming from a black hole in a binary star system in the cluster

d. measure the red-shift of the cluster

e. find a variable star (cepheid or RR Lyrae) in the cluster

10. Our Milky Way Galaxy is what type of galaxy?

a. spiral

b. elliptical

c. dwarf elliptical

d. irregular

e. none of the above

11. You suddenly get an uncontrollable urge to find out more about the other side of the Milky Way Galaxy (the regions beyond the center). Where should you rush off to?

a. the control room of the Hubble Space Telescope at NASA

b. a radio telescope that can observe at 21-cm wavelengths

c. the control room of the Compton Gamma-Ray Observatory

d. a gold mine near Lead, South Dakota

e. the same factory that makes Snickers candy bars

12. Radio astronomy has played a pivotal role in showing us the detailed structure of the Milky Way Galaxy. Which of the following techniques would a radio astronomer use as an essential part of an investigation of this structure?

a. measuring the Doppler shift of a line in a radio spectrum

b. taking a photograph of the sky in the direction of the Big Dipper

c. using a CCD and a filter to record the amount of light from the stars in a nearby open cluster

d. measuring the amount of synchrotron radiation from the Crab Nebula

e. measuring the amount of radio radiation coming from the direction of Jupiter and other planets in the solar system

13. Your weird cousin, who is really into astronomy, decides that the return address he uses on his letters is incomplete! To his city, state, and country, he begins to add: "North America, Earth, Solar System..." If he now wants to include the name of the Galaxy’s spiral-structure feature in which the Earth is located, how should his address end?

a. Cygnus Arm

b. Orion Spur

c. Perseus Arm

d. Sagittarius-Carina Arm

e. Mars arm

Section 25.3: The Mass of the Galaxy

14. A “galactic year” as defined by astronomers is:

a. the time it takes the Earth to go around the Sun (starting with when it’s closest in its orbit to the center of the Galaxy)

b. the time it takes the outermost part of the solar system (the Oort Cloud) to rotate once relative to the Galaxy)

c. the time it took the Milky Way Galaxy to develop spiral arms

d. the time it takes the Sun to revolve once around the center of the Milky Way Galaxy

e. the time it will take the Sun to become a red giant and expand into the Galaxy

15. Objects orbiting around the center of the Milky Way obey Kepler's 3rd Law. This means that:

a. the pull of gravity gets stronger and stronger as you get further away from the center

b. larger clusters of stars will orbit the center more quickly than smaller ones

c. the closer a star is to the center, the longer it will take to go around

d. a cloud of gas or star that is further from the center will generally take more time to orbit

e. the orbits of all objects around the Galaxy are in the shape of a perfect circle

16. How do astronomers measure the mass that the Galaxy contains inside the orbit of the Sun?

a. they count the number of stars one by one and multiply by the average mass of a star

b. they add up all the observations at 21-cm wavelengths (because the mass of hydrogen gas is far greater than the mass in all the stars)

c. they measure the distance to the center of the Galaxy and the period of the Sun's orbit and then use Kepler's Third Law

d. they measure the masses of many other spiral galaxies nearby and then take an average

e. you can't fool me; there is no way to get the mass of something as big as our Galaxy

17. Recently, astronomers have observed stars and other objects that orbit the center of the Milky Way Galaxy farther out than our Sun, but move around faster than we do. How do astronomers think such an observation can be explained?

a. all these faster-moving objects must be escaping from the gravity of the Milky Way and will soon be lost to our Galaxy

b. each of the faster-moving outer objects must be the result of a supernova explosion (giving them extra speed)

c. it is the Sun that is moving too slowly because of a collision billions of years ago; the outer objects are really moving at the appropriate speed for their distance from the center

d. there must be a great deal of invisible dark matter outside the orbit of the Sun whose gravitational pull explains the faster motions we see out there

e. no one can come up with any explanation for this puzzling observation

18. Which of the following statements about dark matter in the Galaxy is FALSE?

a. Most of it cannot at present be observed with our telescopes (we only know its existence from the gravity it exerts)

b. While the dark matter cannot be observed with our present-day instruments, we still have a pretty good idea what it consist of

c. Our measurements suggest that there may be as much as ten or twenty times more dark matter in the Galaxy than the matter we have been able to observe

d. Dark matter appears to be distributed in a giant halo (outer layer) around the Galaxy

e. We can pretty much rule out the idea that the dark matter is made mainly of vast clouds or regions of hydrogen gas

19. Astronomers making observations in our Galaxy have been able to rule out a number of suggestions for what the dark matter in the Galaxy might be. Which of the following have we NOT been able to rule out (which suggestion is still “in the running”)?

a. black holes

b. hydrogen gas that is at low temperatures compared to stars

c. Jupiter-mass planets or brown dwarfs

d. large quantities of dust (like we find in nebulae)

e. a new kind of subatomic particle

Section 25.4: The Center of the Galaxy

20. The very strong source of radio waves at the center of our Galaxy is called

a. Sagittarius A

b. Cygnus X-1

c. the Crab Nebula

d. Milky Way CC1

e. Benford G1

21. Astronomers now think that there is a black hole with more than 4 million times the mass of our Sun at the center of our Galaxy? Roughly how large would the event horizon of such a supermassive black hole be?

a. the size of our Moon

b. about 4 light years across

c. about 17 times the size of the Sun

d. about the size of an atom (so much mass really compresses the event horizon)

e. we can’t answer this question without knowing exactly what kind of stars were swallowed by the black hole

22. Which of the following is NOT part of the growing chain of evidence that makes many astronomers suspect there is a black hole at the very center of the Milky Way Galaxy?

a. the motion of stars close to the center indicates that there is a mass of 4.6 million solar masses inside their orbits

b. the Hubble Space Telescope has shown us a visible-light image of an accretion disk at

the center of the Galaxy

c. the existence of a strong radio source at the center whose size appears to be no larger than Jupiter's orbit

d. the fact that Sagittarius A is a stationary radio source, while objects around it appear to be in motion

e. the observation that matter in the central region continues to be falling in toward the center

23. Astronomers believe that the center of our Galaxy has a black hole with enough mass inside to make almost 4 million Suns! How do astronomers think a black hole could acquire so much mass?

a. the Galaxy formed from one supergiant star, and most of what is left of it is now in the black hole

b. the black hole at the center is really another galaxy that our Milky Way swallowed; none of its material comes from our own Galaxy

c. the center of our Galaxy is a much more crowded region than where the Sun is found; we still see material falling toward the center and material has fallen in for billions of years

d. this black hole contains only dark matter, and we know dark matter is concentrated toward the center of our Galaxy; none of it can be found near the outer regions of the Milky Way

e. no one can think of a way to make a black hole this massive; that’s why most astronomers are skeptical about the observations that indicate that our Galaxy has such a black hole

Section 25.5: Stellar Populations in the Galaxy

24. Where would you look for the youngest stars in the Milky Way Galaxy?

a. in the halo

b. where there is dark matter

c. in the disk

d. in the nuclear bulge

e. you can't fool me; my chances of finding a very young star are the same, wherever in the Galaxy I look

25. If I want to find a sizeable collection of Population II stars in the Milky Way Galaxy, where would be a good place to look?

a. near the Sun

b. in a globular cluster high above the Galaxy's disk

c. in the Orion Spur

d. on the outer surface of giant molecular clouds

e. in an open cluster, especially one with a lot of dust in and around it

26. Astronomers observe the Small Magellanic Cloud (SMC), a not very dense, rather small galaxy near us. They notice that even those stars that formed recently have relatively few heavier elements (when compared to such recent stars in our Milky Way.) What is the likely explanation for this deficiency?

a. most stars in the SMC don't produce their energy through the process of nuclear fusion

b. most stars in the SMC finished going through their lives many billions of years ago

c. because the SMC is small and its stars are widely spaced, the rate of star formation (and star death) is much slower there

d. in small galaxies, only low-mass stars can form (and these do not produce supernovae)

e. astronomers cannot come up with any explanation for this puzzling observation

27. The Population I stars in the Milky Way Galaxy

a. include the Sun

b. show a wider range of ages than Population II stars

c. generally contain a greater percentage of heavier elements than Population II stars

d. are generally found in the disk of the Galaxy

e. all of the above

Section 25.6: The Formation of the Galaxy

28. What leads astronomers to conclude that the proto-galactic cloud (the cloud from which our Galaxy formed) was roughly spherical?

a. all black holes have spherical event horizons

b. the shape of the disk and spiral arm of the Milky Way Galaxy is spherical, so the original cloud must have been too

c. the oldest stars in the Galaxy (Population II stars, globular clusters) form a spherical halo around the Galaxy; they outline the original shape of the cloud that gave the Galaxy birth

d. since the Big Bang that made everything was spherical, all structures in the universe must also be spherical

e. actually, astronomers believe the original proto-galactic cloud was in the shape of a flat disk, like the Galaxy is now

29. Which of the following is evidence that the formation process of our Galaxy may have included collisions with smaller neighbor galaxies?

a. the presence of millions of new stars, recently formed from clouds of gas and dust

b. the existence of supernova remnants, such as the Crab Nebula, in the Galaxy's disk

c. the observation that objects outside the orbit of the Sun are moving around the Galaxy faster than we expected

d. the observation that globular cluster are arranged in a spherical "halo" around the Galaxy

e. the observation of long moving streams of stars that continue to orbit through our Galaxy’s halo

30. What was especially noteworthy about the Sagittarius Dwarf Galaxy when it was discovered among the small galaxies near the Milky Way?

a. it was so large in mass, astronomers could not understand how the Milky Way wasn’t flying toward it

b. it had a supermassive black hole in the center much larger than the Milky Way’s

c. it was rotating so quickly that it could not hold together for very long

d. it was on a collision course with the Milky Way and would be swallowed by it eventually

e. it was made entirely of dark matter and so could not be seen on any photographs

31. In the future, astronomers believe that the Milky Way Galaxy has additional collisions in store. Which of the following nearby galaxies are eventually going to collide with our own?

a. the Small Magellanic Cloud

b. the Large Magellanic Cloud

c. the Andromeda Galaxy (M-31)

d. all of the above

e. none of the above