Deck 19: Galaxies

Question 1

Seyfert galaxies are unique because they have large lobes of radio emission that extend well beyond the visible part of the galaxy.

Answer 1

False

Question 2

Astronomers believe that all giant galaxies probably contain supermassive black holes.

Answer 2

True

Question 3

Dark matter is distributed inside galaxies in exactly the same way as luminous matter,although the total mass of dark matter is much larger than that of luminous matter.

Answer 3

False

Question 4

The type of AGN we see depends mostly on the angle at which we view the galaxy.

Question 5

Star formation in spiral galaxies happens only in the spiral arms.

Question 6

We classify galaxies by

A) their true shapes.
B) how they appear in the sky.
C) the amount of gas and dust in them.
D) whether they are near or far from us.

Question 7

Galaxies that are classified as quasars were much more numerous in the past.

Question 8

Any asymmetry in the gravity field of a spiral galaxy can induce spiral structure.

Question 9

Stars in elliptical galaxies have velocities that

A) are random in direction.
B) are very large in size.
C) are equal in all directions.
D) are constant in time.

Question 10

We can determine the 3-dimensional shape of any individual elliptical galaxy by photographing it.

Question 11

Dark matter consists of material that emits radiation at wavelengths other than visible light.

Question 12

The 3-dimensional shape of an elliptical galaxy depends on the average velocity of its stars along each of the three axes.

Question 13

The 3-dimensional shape of __________ is set by the average velocities of the stars along each of the three axes.

A) spiral galaxies
B) elliptical galaxies
C) elliptical galaxies and spiral bulges
D) quasars

Question 14

Although elliptical and irregular galaxies have been observed in both dwarf and giant varieties,we find only giant spiral galaxies.

Question 15

In spiral galaxies,the size of the central bulge is correlated with the

A) tightness of the spiral arms.
B) luminosity of the galaxy.
C) age of the galaxy.
D) thickness of the disk.

Question 16

We know that spiral galaxies contain dark matter because the gas in the disk rotates with a velocity that decreases in a way that is proportional to .

Question 17

The Hubble tuning fork diagram represents an evolutionary diagram of galaxies from elliptical
to spiral.

Question 18

Today only 30 percent of galaxies are AGN.

Question 19

Approximately __________ of spiral galaxies are barred.

A) 10 percent
B) 25 percent
C) 50 percent
D) 75 percent

Question 20

We know AGN are about the size of our Solar System because of imaging done with the Hubble Space Telescope.

Question 21

Spiral structure

A) rotates at the same speed as the gas in the disk.
B) rotates at a speed that is different than the gas in the disk.
C) stays constant in time as the gas in disk rotates through it.
D) None of the above is true.

Question 22

Roughly what percentage of the total mass of a galaxy is made up of luminous,or normal,matter?

A) 5 percent
B) 25 percent
C) 50 percent
D) 90 percent

Question 23

Which of the following is NOT a difference between spiral and elliptical galaxies?

A) Spiral galaxies still have ongoing star formation whereas elliptical galaxies do not.
B) Spiral galaxies have dark matter halos whereas elliptical galaxies do not.
C) Spiral galaxy disks contain lots of cold gas and dust whereas elliptical galaxies do not.
D) Spiral galaxies tend to be bluish whereas elliptical galaxies tend to be reddish.

Question 24

Active star formation does not occur in elliptical galaxies because they

A) rotate too fast.
B) contain little molecular hydrogen.
C) are too massive.
D) are too far away.

Question 25

Why is 21-cm radiation a good spiral arm tracer?

A) Emitted by neutral hydrogen,it traces the location of concentrations of gas.
B) Emitted by O and B stars,it traces the location of newly formed stars.
C) Emitted by ionized hydrogen,it traces the location of H II regions.
D) Emitted by molecular hydrogen,it traces the location of clouds in the process of collapsing into stars.

Question 26

Which of the following are NOT predominantly found in the spiral arms of galaxies?

A) Molecular clouds
B) H II regions
C) K- and M-type stars
D) Type II supernovae

Question 27

Elliptical galaxies appear red because

A) they are moving away from us.
B) they contain mostly ionized hydrogen gas.
C) they contain mostly old stars.
D) they contain lots of dust.

Question 28

What makes up the majority of the mass of an individual spiral galaxy?

A) A central supermassive black hole
B) Dark matter
C) Massive O- and B-type stars
D) Cold molecular gas clouds

Question 29

Long-lasting spiral density waves occur in the disk of a spiral galaxy when

A) the spiral merges with another galaxy.
B) the galaxy is too close.
C) the galaxy's disk is regularly disturbed.
D) None of the above

Question 30

What could you use to measure the mass of the dark matter halo in a spiral galaxy?

A) H $\Pi$ emission from H II regions in the spiral disk
B) The velocities of satellite dwarf galaxies surrounding a spiral galaxy
C) Absorption lines in the spectra of its globular clusters
D) All of the above

Question 31

The dark matter in galaxies is __________ the luminous material.

A) distributed in roughly the same way as
B) much more extended in radius than
C) much more centrally concentrated than
D) much less uniform in density than

Question 32

Quasars were first discovered in which region of the electromagnetic spectrum?

A) X-ray
B) Cosmic ray
C) Radio
D) Infrared

Question 33

How did astronomers determine that elliptical galaxies are composed mostly of dark matter?

A) They measured X-ray emission from hot gas gravitationally bound to the galaxies.
B) They measured the rotation rates of gas as a function of distance from the centers of the galaxies.
C) They measured the amount of gravitational pull elliptical galaxies have on companion galaxies.
D) They assumed that the proportion of dark matter was roughly the same as in spiral galaxies.

Question 34

Spiral structure can be triggered in a disk galaxy by

A) a close encounter with a passing galaxy.
B) an orbiting dwarf galaxy.
C) an off-center burst of star formation in the disk.
D) All of the above

Question 35

If the rotational speed of the gas in the disk of a spiral galaxy is 200 km/s at a distance of 80,000 light-years from its center,then what is the mass enclosed within this radius?

A)
B)
C)
D)

Question 36

Which of the following would NOT be found in an elliptical galaxy?

A) Novae
B) Type I supernovae
C) Type II supernovae
D) Planetary nebulae

Question 37

A galaxy rotation curve is a plot of the rotation speed as a function of the

A) galaxy's luminosity.
B) mass of the dark matter halo.
C) brightness of the luminous matter in the galaxy.
D) radius from the center.

Question 38

The disks of spiral galaxies appear blue because

A) spiral galaxies are moving toward us.
B) spiral galaxies contain mostly hot blue stars.
C) spiral galaxies are still undergoing star formation.
D) spiral galaxies contain more metals that,when ionized,emit blue light.

Question 39

Why do rotation curves of galaxies imply that dark matter exists?

A) The velocity of stars rises dramatically at large distances from the centers of galaxies,implying large amounts of dark matter cause these stars to move much faster than stars at smaller distances.
B) The velocity of stars stays somewhat constant at distances beyond the visible edges of galaxies,implying that more matter than what we observe in stars and gas must be there.
C) The velocity of stars is low in the inner regions of galaxies,suggesting that dark matter is impeding their motion.
D) The velocity of stars rises quickly in the inner regions of galaxies,suggesting that unseen matter is gravitationally moving this material at faster rates than expected.

Question 40

If a galaxy had no dark matter,how would the velocity (v)of a star that orbited far outside the visible extent of the galaxy depend on its distance (r)from the center of the galaxy?

A)
B)
C)
D)

Question 41

What do the formation of the Solar System and the existence of AGNs have in common?

A) They both demonstrate the importance of how luminosity varies with time.
B) They both demonstrate the high efficiency of nuclear fusion.
C) They both demonstrate the importance of accretion disks.
D) They both demonstrate the importance of living in the center of a galaxy.

Question 42

How do we know that AGN have sizes on the order of our Solar System?

A) Quasars and Seyfert galaxies are stellar-like sources.
B) Their brightness varies by factors of a few.
C) The emission lines in their spectra show gas rotating at speeds of thousands of km/s.
D) Their brightness varies on timescales of hours to a day.

Question 43

What happens to active galaxies when their AGNs run out of fuel?

A) The black holes powering them collapse even further.
B) They simply become normal galaxies.
C) They slowly dissipate into clouds of gas and dust.
D) They eventually pull in material from farther out,starting the AGN process all over again.

Question 44

If a Seyfert galaxy's nucleus varies in brightness on the timescale of 10 hours,then approximately what is the size of the emitting region?

A) 20 AU
B) 70 AU
C) 90 AU
D) 140 AU

Question 45

Assume that when a supermassive black hole accretes gas,approximately 50 percent of its mass is converted directly into energy,which is radiated away.If a quasar has a luminosity of then what must its mass accretion rate be?

A) per year
B) per year
C) per century
D) per million years

Question 46

How do the current star formation rates of spiral and elliptical galaxies compare?

Question 47

By what are the real shapes of galaxies defined?

Question 48

If the average quasar has a luminosity of and an absolute magnitude of -40 and you discover one that has an apparent magnitude of +9,then what is its distance?

A) 600 Mpc
B) 200 Mpc
C) 100 Mpc
D) 50 Mpc

Question 49

The unified model of AGN suggests that quasars,Seyfert galaxies,and radio galaxies

A) are similar phenomena but viewed from different orientation angles.
B) are powered by similar mass accretion rates onto supermassive black holes.
C) are driven by violent mergers of two gas-rich spiral galaxies.
D) are unrelated,although they are all very luminous galaxies at radio wavelengths.

Question 50

Describe two ways by which spiral structure may be induced in a spiral galaxy's disk.

Question 51

What do the broad emission lines in quasar spectra tell astronomers about these objects?

A) They are very far away.
B) They are moving away from us.
C) They have rapid internal motions.
D) They are very dense.

Question 52

What is a rotation curve,and what can it tell us about a galaxy?

Question 53

We interpret the fact that we saw more AGNs in the past than we do today to indicate that

A) there were fewer galaxy-galaxy interactions in the past.
B) there were more galaxy-galaxy interactions in the past.
C) supermassive black holes were larger in the past.
D) today's AGNs are primarily hidden by large amounts of cold gas and dust.

Question 54

In some radio galaxies,we only see one side of the jet because

A) the black hole only produces a jet in one direction.
B) of relativistic beaming.
C) the other side is inside the black hole's event horizon.
D) of dust obscuration.

Question 55

What is the approximate percentage of nearby galaxies that contain AGN?

A) 3 percent
B) 15 percent
C) 40 percent
D) 80 percent

Question 56

AGNs appear to be powered by

A) supermassive black holes.
B) extremely dense star clusters.
C) ultradense molecular clouds.
D) dark matter.

Question 57

More luminous giant galaxies tend to have __________ supermassive black holes at their centers.

A) more massive
B) radio quiet
C) more luminous
D) slower rotating

Question 58

If the rotational speed of the gas in the disk of a spiral galaxy is 100 km/s at a distance of 26,000 light-years from its center,then what is the mass enclosed within this radius? If the mass of luminous matter inside this radius is 5 billion then what fraction of the galaxy's mass is made of dark matter?

Question 59

The observed redshifts of quasars tell us all of the following EXCEPT

A) quasars are extremely luminous.
B) quasars are rare in the universe today.
C) quasars are incredibly far from us.
D) quasars are extremely massive.

Question 60

How did Hubble use his tuning fork diagram to classify galaxies? Is there any significance to this organization?

Question 61

How do astronomers know that AGNs are as small as our Solar System?

Question 62

Why is our own galaxy not an active galaxy today?

Question 63

What is the connection between active galaxies and galactic mergers?

Question 64

What is the most likely candidate for making up the dark matter in galaxies?

Question 65

What is the difference between a Seyfert galaxy and a normal spiral galaxy?

Question 66

Once we get outside the dark matter halo of a galaxy,how should the speed of an orbiting body such as a satellite dwarf galaxy depend on its distance from the giant galaxy's center?

Question 67

Give three examples of types of active galactic nuclei and give one reason why each is unique.

Question 68

If the radio lobes of a radio galaxy extend out to 10 Mpc from the center of the galaxy and the particles in them are traveling at approximately 0.99 c,then how long must the black hole at the center have been ejecting this material into space? Note that and .

Question 69

If an AGN varies its brightness on a timescale of 4 hours,then what is the size of the AGN measured in AU?