Deck 13: Galaxies: Normal and Active

Question 1

A megaparsec is equivalent to

A) 3.26 light-years.
B) 206,265 AU.
C) the age of our solar system.
D) a million parsecs.
E) the diameter of the Milky Way galaxy.

Answer 1

a million parsecs.

Question 2

Poor clusters

A) contain more than 1000 stars and are found in the halo of the galaxy.
B) contain lots of young stars and are found in the disk of a spiral galaxy.
C) contain more than 1000 galaxies and are generally elliptical in shape.
D) contain fewer than 1000 galaxies and tend to be irregularly shaped.
E) are found in the nucleus of the galaxy.

Answer 2

contain fewer than 1000 galaxies and tend to be irregularly shaped.

Question 3

___ can be used to determine the galaxy's mass if the galaxy is reasonably close, so that the Doppler shift of the galaxy disk material can be measured at several distances from the galaxy's center relative to the center.

A) The Hubble constant
B) A galaxy's color
C) A galaxy's rotation curve
D) A galaxy's diameter
E) The velocity dispersion method

Answer 3

A galaxy's rotation curve

Question 4

The Milky Way is part of

A) I and III
B) I and IV
C) II and III
D) II and IV
E) just III

Question 5

Gravitational lensing

A) occurs when light passes near a massive object and is deflected by the object's gravitational field.
B) can be used to determine the luminosity of a galaxy.
C) occurs when the mass of a galaxy is greater than expected from the luminosity of the galaxy.
D) occurs when the mass of a galaxy is less than expected from the luminosity of the galaxy.
E) can be used to determine the recessional velocity of a galaxy.

Question 6

____ have elongated nuclei with spiral structure extending from the ends of the elongations. The Milky Way is a member of this class of galaxy.

A) Spiral galaxies
B) Barred spiral galaxies
C) Elliptical galaxies
D) Irregular galaxies
E) S0 galaxies

Question 7

____ are produced when two galaxies pass near each other and pull large streamers of stars, gas, and dust away from the galaxies.

A) Ring galaxies
B) Spiral galaxies
C) Rotation curves
D) Tidal tails
E) Irregular galaxies

Question 8

The look-back time is

A) the time it takes for the light from an object to reach Earth.
B) numerically equal to the distance in light-years.
C) smaller for more distant objects.
D) all of the above.
E) a and b above.

Question 9

The Hubble law is a relation between a galaxy's

A) mass and its luminosity.
B) distance and its luminosity.
C) mass and its recession velocity.
D) distance and its recession velocity.
E) mass and its diameter.

Question 10

The total mass of galaxies in a cluster of galaxies divided by the number of galaxies in the cluster can be used to determine a typical galaxy's ____

A) luminosity.
B) distance.
C) mass.
D) diameter.
E) age.

Question 11

Most of the mass of a galaxy is contained in the

A) massive O and B stars in the galaxy.
B) H I regions of the galaxy.
C) H II regions of the galaxy.
D) dark matter of the galaxy.
E) disk of the galaxy.

Question 12

A mega-parsec (Mpc) is equivalent to

A) 3.26 light-years.
B) 206,265 light years.
C) 1,000,000 light years
D) 3,260,000 light-years.
E) the diameter of the Milky Way galaxy.

Question 13

The cluster method (motions of galaxies in a cluster of galaxies) can be used to determine the cluster's

A) luminosity.
B) distance.
C) mass.
D) diameter.
E) age.

Question 14

A spiral (S or SB) galaxy contains

A) mostly lower-main-sequence stars and giants.
B) mostly upper-main-sequence stars and giants.
C) mostly upper-main-sequence stars and gas and dust.
D) upper- and lower-main-sequence stars and gas and dust.
E) mostly white dwarfs and supergiants.

Question 15

Mathematical models indicate that ____ galaxies are produced by high-speed collisions in which a smaller galaxy passes through another galaxy almost perpendicular to the disk of the galaxy.

A) ring
B) spiral
C) antenna
D) irregular
E) tidal tail

Question 16

An irregular galaxy contains mostly

A) lower-main-sequence stars and giants.
B) upper-main-sequence stars and giants.
C) upper-main-sequence stars and gas and dust.
D) upper- and lower-main-sequence stars and gas and dust.
E) white dwarfs and supergiants.

Question 17

An elliptical (E) galaxy contains

A) mostly lower-main-sequence stars and giants.
B) mostly upper-main-sequence stars and giants.
C) mostly upper-main-sequence stars and gas and dust.
D) roughly equal numbers of upper- and lower-main-sequence stars.
E) mostly white dwarfs and supergiants.

Question 18

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 methods.
E) none of these methods.

Question 19

Which of the following is not used as a distance indicator for galaxies?

A) large globular clusters
B) Herbig-Haro objects
C) H II regions
D) cepheid variable stars
E) supernovae

Question 20

A ____ generally contains well over 1000 galaxies and is quite dense. They often contain many giant elliptical galaxies.

A) local group
B) poor cluster
C) rich cluster
D) tidal tail
E) quasar

Question 21

What factors are important when trying to classify a spiral galaxy?

A) amount of dust and gas in the galaxy
B) structure of the spiral arms
C) size of the central region
D) All of the these are important.

Question 22

What distance method did Edwin Hubble use to determine the distance to local galaxies?

A) Hubble Law
B) supernova observations
C) period-luminosity relationship of variable stars
D) parallax

Question 23

If a galaxy has a radial velocity of 8000 km/s and the Hubble constant is 70 km/s/Mpc, what is the distance to this galaxy?

A) 8.75*0³ Mpc
B) 2.4*10⁹ Mpc
C) 5.6*10⁵ Mpc
D) 114 Mpc
E) 8.75*10^-3 Mpc

Question 24

Supermassive black holes are believed to be located at the center of many galaxies because

A) the rotation curve of the galaxy indicates that 90% of the galaxy is dark matter.
B) the orbital motion of material near the center is very fast and indicates a very massive core.
C) the shape of the bulge in all spiral galaxies can only be supported by a supermassive black hole.
D) the spiral structure requires a black hole to maintain the spiral arms.
E) the orbital speeds of a globular clusters in the galaxy are greater than the speed of light.

Question 25

Astronomers now speculate that a galaxy's shape depends on all of the following except

A) the rate of star formation.
B) the history of past collisions.
C) the mass.
D) All of these may be important in determining a galaxy's shape.

Question 26

It is believed that ring galaxies form

A) when two galaxies collide nearly head on at high speed.
B) when two spiral galaxies collide, but not directly head on.
C) from a large cloud of gas and dust with very little angular momentum.
D) from a large cloud of gas and dust with a very high angular momentum.
E) when more than two galaxies collide at the same time.

Question 27

The Milky Way galaxy is part of

A) the Virgo cluster.
B) the Large Magellanic Cloud.
C) the Small Magellanic Cloud.
D) the Local Group.
E) a rich cluster.

Question 28

If H equals 70 km/s/Mpc, then a galaxy with a radial velocity of 2100 km/s has a distance of approximately

A) 2170 Mpc.
B) 2030 Mpc.
C) 30 Mpc.
D) 0.03 Mpc.
E) 147,000 Mpc.

Question 29

Which of the following is the largest object?

A) the Milky Way galaxy
B) the Large Magellanic Cloud
C) the Local Group
D) the Andromeda galaxy

Question 30

An elliptical galaxy could

A) evolve into an irregular galaxy when it has used up all of its gas and dust.
B) be formed from the collision and merger of spiral galaxies.
C) evolve from a single spiral galaxy when the spiral has used up all of its gas and dust.
D) become a starburst galaxy if it were to move through the hot intergalactic medium of a cluster.
E) evolve from an S0 galaxy if the S0 galaxy were to increase its rotation rate.

Question 31

The Virgo cluster

A) is the galactic cluster that contains the Milky Way.
B) is the oldest known cluster of galaxies.
C) is located at the center of the universe.
D) contains mostly spiral galaxies and very few elliptical galaxies.
E) is a rich cluster and the closest cluster of galaxies outside of the Local Group.

Question 32

____ galaxies contain large clouds of gas and dust, both young and old stars, but have no obvious spiral arms or nucleus.

A) Irregular
B) S0
C) E7
D) Sa
E) E0

Question 33

If the absolute magnitude, M, of a supernova is -19 and a galaxy is found that contains a supernova with an apparent magnitude, m, of 16. What is the distance to the galaxy? Hint: d_pc = 10^{(m - M + 5)/5}

A) 100 AU
B) 100 pc
C) 100 ly
D) 100 kpc
E) 100 Mpc

Question 34

Galactic cannibalism refers to

A) binary galaxies.
B) the merging of galaxies.
C) galaxies drawing in gas from the intergalactic medium.
D) the destruction of a galaxy's globular clusters by the galaxy's nucleus.
E) none of these.

Question 35

The rotation curve of a galaxy can be used to determine

A) the relative number of hot young stars in the galaxy.
B) the relative amount of gas and dust in the galaxy.
C) the radius of the galaxy.
D) the luminosity of the galaxy.
E) the mass of the galaxy.

Question 36

What is the Hubble constant essentially a measure of?

A) the number of galaxies in the universe
B) the expansion of the universe
C) the age of the Milky Way galaxy
D) the amount of dark matter in an average galaxy

Question 37

Observations of galaxies and clusters of galaxies indicate that about ____ percent of the matter in the universe is dark matter.

A) 5
B) 25
C) 35
D) 45
E) 95

Question 38

If Galaxy A is found to have a recessional velocity four times greater than Galaxy B, what can you say about their relative distances from Earth?

A) Galaxy A is four times closer than Galaxy B.
B) Galaxy A is four times further away than Galaxy B.
C) Galaxy A is twice as distant than Galaxy B.
D) Galaxy A is twice as close than Galaxy B.

Question 39

Starburst galaxies

A) contain a large number of very young stars, but very little evidence of gas clouds.
B) contain a large number of very old stars and almost no gas or dust.
C) are often associated with a galaxy that is colliding with another galaxy.
D) are common in rich clusters.
E) are composed of filaments and voids.

Question 40

What is the primary factor in determining the classification for an elliptical galaxy?

A) size
B) shape
C) mass
D) color

Question 41

What distance methods is(are) used to calibrate the Hubble constant?

A) parallax
B) supernova observations
C) variable stars
D) both a and b
E) both b and c

Question 42

If the redshifts of quasars arise from the expansion of the universe yet they have brighter magnitudes than galaxies with the same redshifts, the quasar must

A) be very small.
B) be within the Local Group.
C) be a single star with an extremely large mass.
D) be moving toward Earth with a large radial velocity.
E) emit a very large amount of energy per second.

Question 43

What distance method is used to determine the distance to the most distant galaxies when only a redshift is measured?

A) Hubble's law
B) supernova observations
C) period-luminosity relationship of variable stars
D) parallax

Question 44

The letters AGN stand for

A) three spectral types of stars.
B) active planet.
C) active star.
D) active galaxy nucleus.
E) none of the above.

Question 45

The fact that many radio lobes emit more intensely from the side away from the galaxy suggests that

A) they are formed by material falling into the galaxy.
B) they are powered by magnetic fields.
C) they are excited by radiation from nearby galaxies.
D) they are powered by the rapid rotation of the galaxy.
E) they are created by jets from the galaxy emitting where the material is halted.

Question 46

In the double-exhaust model, the radio lobes of a radio galaxy are inflated by

A) jets of excited gas flowing from the central galaxy.
B) jets of high-energy sound waves flowing from the central galaxy.
C) a disk of ionized material that orbits very near a supermassive black hole.
D) dark clouds of very cold gas and dust.
E) none of the above.

Question 47

When discovered in the 1960's, a(n) ____ was found to emit large amounts of energy, but through visual and radio telescopes appeared to be a single point of light much like a star.

A) a planet like Venus
B) E galaxy
C) spiral galaxy
D) double-lobed radio galaxy
E) quasar

Question 48

What distance method is used to determine the distance to the most distant galaxies?

A) radar echo
B) supernova observations
C) period-luminosity relationship of variable stars
D) parallax

Question 49

The energy from an AGN is produced by

A) the collision of two spiral galaxies.
B) the collision of two elliptical galaxies.
C) the collision of two radio jets.
D) matter flowing into a supermassive black hole.
E) supernovae.

Question 50

The radio lobes that are on each side of some radio galaxies and jets from them produce mainly

A) 21-cm radiation.
B) synchrotron radiation.
C) black body radiation.
D) emission lies due to hydrogen.
E) absorption lines due to hydrogen.

Question 51

What type of galaxies do astronomers believe to be the most common?

A) elliptical
B) spiral
C) irregular
D) Astronomers have no idea which type of galaxy is most common.

Question 52

_____ galaxies contain a supermassive black hole at their centers while active nuclei are present in _____of galaxies

A) Most; a few percent
B) Most; the majority
C) A small minority; a few percent
D) A small minority; the majority

Question 53

All ____ galaxies are spiral galaxies that have small, luminous nuclei.

A) active
B) radio
C) Seyfert
D) double-lobed radio
E) blazar

Question 54

We suspect that quasars are the active centers of galaxies because

A) "fuzz" around the central luminous regions produces spectra like a collection of normal stars.
B) a few quasars have large redshifts.
C) the central regions of some quasars fluctuate rapidly.
D) all of the above.
E) none of the above.

Question 55

Centaurus A is a radio galaxy that has a visible galaxy at the center. This central elliptical galaxy of Centaurus A is encircled by a ring of gas and dust, different from most elliptical galaxies. The dust ring orbits about an axis that is perpendicular to the axis of rotation of the elliptical galaxy. What does this suggest about this central elliptical galaxy of Centaurus A?

A) The radio jets have caused the dust disk to be driven around the elliptical galaxy.
B) There are at least two black holes at the center of the elliptical galaxy.
C) Centaurus A is probably the result of a merger of an elliptical galaxy and a spiral galaxy.
D) Dust is produced as the jets interact with the intergalactic medium.
E) Elliptical galaxies often contain dust that forms a disk along their rotation axis.

Question 56

The central galaxy in a double-lobed radio source is usually

A) an irregular galaxy.
B) a spiral galaxy.
C) a dwarf elliptical galaxy.
D) a giant elliptical galaxy.
E) a quasar.

Question 57

The hot spots in a double-lobed radio source

A) appear to coincide with the location of the central galaxy responsible for the jets.
B) are where hot excited gas interacts with the intergalactic medium.
C) are only found near quasars.
D) produce enough visible energy to be imaged at visible wavelengths.
E) are always perpendicular to each other.

Question 58

Soon after discovery, it was observed that quasars had a starlike appearance which was blurred by Earth's atmospheric "seeing". Despite the blurring, it was realized that the intense energy-emitting regions of quasars must be small because they

A) have high radial velocities.
B) are very luminous.
C) are surrounded by quasar fuzz.
D) radiate huge amounts of energy.
E) fluctuate rapidly on time scales as short as a few hours.

Question 59

That the radio lobes radiate synchrotron radiation indicates that

A) high-speed electrons are spiraling through a magnetic field.
B) the source of the radio jets must be a black hole.
C) the source of the radio energy is rotating rapidly.
D) the central galaxy must be a giant elliptical galaxy.
E) the central galaxy must rotate about two nearly perpendicular axes.

Question 60

The discovery of the gravitational lens effect for quasars

A) shows that quasars were located within the local group of galaxies.
B) shows that quasars were giant planets in our solar system.
C) shows that quasars are much further away than the distant galaxy that forms the gravitational lens.
D) proves Newton's theory of gravitation by showing that the photon is affected by gravity.
E) proves the existence of supermassive black holes at the center of active galactic nuclei.

Question 61

Quasars are most common with redshifts

A) less than 0.1
B) less than 0.5
C) of about 2
D) greater than 6
E) greater than 8

Question 62

Galaxies may contain a supermassive black hole at their center but _____ an active nucleus because of _______ into the black hole

A) show; mass inflow
B) not show; mass inflow
C) show; lack of mass inflow

Question 63

If a quasar has a recessional velocity of 2.7*10⁵ km/s and is determined to be 3600 Mpc, what is the Hubble constant based on this quasar alone? Hint: Not that the units of your result should be (km/s)/Mpc to see what arithmetic process you need to perform.

A) 50 km/s/Mpc
B) 9.7*10⁸ (km/s)Mpc
C) 75 km/s/Mpc
D) 0.013 km/s/Mpc
E) 273,600 km/s/Mpc

Question 64

____ show(s) that some quasars are further away than distant galaxies and that space time is curved by massive objects.

A) Double-lobed radio galaxies
B) Blazars
C) The gravitational lens effect
D) Head-tail galaxies
E) Superluminal expansion

Question 65

Why do astronomers believe supermassive black holes are the source of an AGN's energy?

A) Such black holes have been found at the center of most galaxies, both active and inactive.
B) Radio jets are seen from low-mass black holes plus accretion disks inside our galaxy.
C) Jets and accretion disks have been observed in active galaxies.
D) Black holes can produce so much energy in such a small place.
E) all of the above

Question 66

According to the unified model of active galactic nuclei, a ____ is observed if our line of sight is parallel to the plane of the dense disk of an active galactic nucleus (the direct view of the nucleus is blocked by dust in the disk).

A) planet
B) Type 1 Seyfert (broad spectral emission lines with narrow cores, X-ray and UV luminous)
C) Type 2 Seyfert (narrow spectral emission lines, weaker X-ray emission)

Question 67

The unified model describes active galactic nuclei using

A) a supermassive black hole at the center of a normal spiral galaxy.
B) a supermassive black hole surrounded by an accretion disk and dense disk of gas.
C) an accretion disk around a neutron star.
D) gravitational lenses to intensify the radiation coming from them.
E) different lines of sight toward and dwarf irregular galaxy.

Question 68

In the unified model of active galactic nuclei, the broad line region in an active galactic nucleus is

A) composed of clouds of gas and stars moving at very high orbital velocities near a supermassive black hole.
B) composed of a supermassive black hole surrounded by empty space.
C) responsible for producing the bright continuous radiation from within the event horizon.
D) responsible for the narrow absorption lines seen in Type 2 Seyfert galaxies.
E) located far from the core beyond the disk of stars of the galaxy.

Question 69

How do astronomers know that the luminous regions of active nuclei of active galaxies are very small?

A) Their nuclei are much brighter than expected.
B) The orbits of stars near the center of the galactic nuclei are faster than expected.
C) The luminosity of the nuclei varies over short times.
D) The color of the nuclei is different than expected.

Question 70

The hydrogen Balmer line H _$\gamma$ has a wavelength of 434.0 nm in the laboratory. It is observed in a quasar at 651.0 nm. In terms of the speed of light, c, what is the recessional velocity of this quasar?

A) 217.0c
B) 2c
C) 1.5c
D) 0.67c
E) 0.5c

Question 71

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

A) Normal spiral galaxies usually have shorter spiral arms.
B) Normal spiral galaxies never contain a supermassive black hole at their center.
C) The central region of a Seyfert galaxy is much brighter.
D) Seyfert galaxies don't contain any star formation.

Question 72

The hydrogen Balmer line H _$\beta$ has a wavelength of 486.1 nm in the laboratory. It is observed in a quasar at 2430.5 nm. What is the change in wavelength (in nm) of this quasar? Is it a "redshift" or "blueshift"?

A) 0; no change
B) 2430.5; redshift
C) 486.1; blue shift
D) 1944.4; blueshift
E) 1944.4; redshift

Question 73

What was the first evidence that quasars were different from astronomical objects before they were observed in visual wavelengths?

A) The first quasars were seen to have fuzz.
B) Quasars emitted radio energy like active galaxies, but appeared to be point sources in radio wavelengths.
C) Quasars showed significant gravitational lens effects.
D) The spectra of quasars looked like that of an M dwarf.
E) The larger redshifts originally indicated that they were orbiting the center of the Milky Way.

Question 74

According to the unified model of active galactic nuclei, ____ is in the center surrounded by _________with a Type 1 Seyfert or Type 2 Seyfert being seen depending on the viewing angle.

A) a supermassive black hole; an accretion disk
B) a supermassive black hole; empty space
C) no black hole; an accretion disk
D) no black hole; empty space

Question 75

Statistical evidence

A) can be used to draw conclusions about a specific cases.
B) is applicable to classes of objects where only a few objects from the class have been studied.
C) allows scientists to determine the mechanism that produces the dust ring in Centaurus A.
D) allows scientists to deduce general characteristics about a class of objects with similar properties.
E) provides insight into the behavior of an individual object based on careful observations of it.

Question 76

How are astronomers able to determine that quasars are so small?

A) They are variable over a short period of time.
B) They emit mainly X-rays.
C) They are only found at very large distance.
D) The structure of a quasar is completely resolved in images.

Question 77

____ is (are) observed when light from a distant quasar travels past a massive galaxy between us and the quasar, and this light is focused to form two or more images of the same quasar.

A) A double-lobed radio galaxy
B) Superluminal expansion
C) The gravitational lens effect
D) A blazar
E) Gravitational waves

Question 78

If Hubble's constant is taken to be 70 km/s/Mpc, and a quasar is found with a radial velocity of 0.95 times the speed of light, how far away is the quasar?

A) 4100 Mpc
B) 0.014 Mpc
C) 67 Mpc
D) 74 Mpc
E) 300,000 Mpc

Question 79

The hydrogen Balmer line H _$\beta$ has a wavelength of 486.1 nm in the laboratory. It is observed in a quasar at 2430.5 nm. What is the fractional change in wavelength or redshift z of this quasar?

A) 5
B) 0.5
C) 0.25
D) 4
E) 1944.4

Question 80

Evidence that supports quasars being the nuclei of very distant galaxies includes

A) the existence of quasar fuzz.
B) the observation of a supernova near a quasar whose distance from its brightness is consistent with the large redshift.
C) gravitational lensing of some quasars by nearby galaxies.
D) all of the above.
E) none of the above.