Deck 20: Galaxies and the Foundations of Modern Cosmology

Question 1

Which of the following types of galaxies are most commonly found in large clusters?

A)spirals
B)ellipticals
C)lenticulars
D)irregulars

Answer 1

B

Question 2

Based on counting the number of galaxies in a small patch of the sky and multiplying by the number of such patches needed to cover the entire sky,the total number of galaxies in the observable universe is estimated to be approximately

A)100 million.
B)1 billion.
C)10 billion.
D)100 billion.
E)1 trillion.

Answer 2

D

Question 3

What is the major difference between an elliptical galaxy and a spiral galaxy?

A)A spiral galaxy contains mostly younger stars.
B)A spiral galaxy has a spherical halo.
C)An elliptical galaxy lacks a disk component.
D)Elliptical galaxies are not as big as spiral galaxies.
E)There are no dwarf spiral galaxies,but there are dwarf ellipticals.

Answer 3

C

Question 4

How was Edwin Hubble able to use his discovery of a Cepheid in Andromeda to prove that the "spiral nebulae" were actually entire galaxies?

A)There are no Cepheids in the Milky Way,so his discovery proved that it had to be in another galaxy.
B)He measured the stellar parallax of the Cepheid in Andromeda,was able to determine the distance to it,and showed that it was far outside the Milky Way Galaxy.
C)From the period-luminosity relation for Cepheids,he was able to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.
D)Since a Cepheid is a type of luminous galaxy,when he found it in Andromeda he was able to prove that Andromeda was a separate galaxy from the Milky Way.

Question 5

How does a lenticular galaxy differ from a normal spiral galaxy?

A)It has no bulge.
B)It has an elongated bulge resembling a bar more than a sphere.
C)It is flatter in shape.
D)It has no gas or dust.
E)It has no spiral arms.

Question 6

What two quantities did Edwin Hubble plot against each other to discover the expansion of the Universe?

A)velocity and distance
B)luminosity and distance
C)velocity and temperature
D)luminosity and temperature
E)age and distance

Question 7

Which of the following types of galaxies are most spherical in shape?

A)spirals
B)ellipticals
C)lenticulars
D)irregulars

Question 8

How did Edwin Hubble measure the distance to the Andromeda Galaxy?

A)He measured its parallax.
B)He applied the period-luminosity relation to Cepheid variables.
C)He deduced it from its redshift.
D)He used white dwarf supernovae.

Question 9

The disk component of a spiral galaxy includes which of the following parts?

A)halo
B)bulge
C)spiral arms
D)globular clusters
E)all of the above

Question 10

What is a standard candle?

A)an object for which we are likely to know the true luminosity
B)an object for which we can easily measure the apparent brightness
C)a class of objects in astronomy that all have exactly the same luminosity
D)any star for which we know the exact apparent brightness
E)a long,tapered candle that lights easily

Question 11

Which types of galaxies have a clearly defined disk component?

A)spirals only
B)ellipticals only
C)lenticulars only
D)irregulars only
E)spirals and lenticulars

Question 12

Compared to spiral galaxies,elliptical galaxies are

A)redder and rounder.
B)redder and flattened.
C)bluer and rounder.
D)bluer and flattened.
E)always much smaller.

Question 13

Approximately how many stars does a dwarf elliptical galaxy have?

A)1 trillion
B)100 billion
C)10 billion
D)less than a billion
E)less than a million

Question 14

Which of the following statements about galaxies is true?

A)Small galaxies outnumber large galaxies and produce most of the light in the universe.
B)Small galaxies outnumber large galaxies but large galaxies produce most of the light in the universe.
C)There is an approximately equal number of small and large galaxies in the universe and together they each contribute an equal amount of light.
D)Most galaxies in the universe are about the same size as the Milky Way.
E)Galaxies come in a wide variety of shapes and sizes but are all very blue in color.

Question 15

Which types of galaxies have a clearly defined halo component?

A)spirals only
B)ellipticals only
C)lenticulars only
D)irregulars only
E)all but irregulars

Question 16

Most large galaxies in the universe are

A)elliptical.
B)spiral or lenticular.
C)irregular.
D)abnormal.

Question 17

Suppose that we look at a photograph of many galaxies.Assuming that all galaxies formed at about the same time,which galaxy in the picture is the youngest?

A)the one that is reddest in color
B)the one that is bluest in color
C)the one that is farthest away
D)the one that is closest to us
E)the one that appears smallest in size

Question 18

Why are Cepheid variables important?

A)Cepheid variables are stars that vary in brightness because they harbor a black hole.
B)Cepheids are pulsating variable stars,and their pulsation periods are directly related to their true luminosities.Hence,we can use Cepheids as "standard candles" for distance measurements.
C)Cepheids are a type of young galaxy that helps us understand how galaxies form.
D)Cepheids are supermassive stars that are on the verge of becoming supernovae and therefore allow us to choose candidates to watch if we hope to observe a supernova in the near future.

Question 19

Which of the following types of galaxies are reddest in color?

A)spirals
B)ellipticals
C)lenticulars
D)irregulars

Question 20

Which of the following is true about irregular galaxies?

A)They are composed solely of old stars.
B)They generally have significant bulge populations.
C)They were more common when the universe was younger.
D)They have reddish colors.
E)They have well defined spiral arms.

Question 21

Although it is difficult to tell from our vantage point inside the galaxy,astronomers suspect that the Milky Way is a barred spiral.

Question 22

Stars are continually forming in the halo of our Galaxy today.

Question 23

Which of the following is a consequence of Hubble's Law?

A)the Big Bang
B)all galaxies are moving away from us equally fast
C)the more distant a galaxy is from us,the faster it moves away from us
D)the closer a galaxy is to us,the faster it moves away from us
E)more distant galaxies appear younger

Question 24

What is the most accurate way to determine the distance to a nearby star?

A)radar ranging
B)stellar parallax
C)using Cepheid variables
D)Hubble's law

Question 25

What is the primary practical difficulty that limits the use of Hubble's law for measuring distances?

A)Redshifts of galaxies are difficult to measure.
B)The recession velocities of distant galaxies are so great that they are hard to measure.
C)We do not know Hubble's constant very accurately yet.
D)Hubble's law is only useful theoretically;it is difficult to use in practice.
E)The motion of Earth relative to the Milky Way is difficult to account for.

Question 26

Dr.X believes that the Hubble constant is H₀ = 55 km/s/Mpc.Dr.Y believes it is H₀ = 80 km/s/Mpc.Which statement below automatically follows?

A)Dr.X believes that the universe is expanding,but Dr.Y does not.
B)Dr.X believes that the Andromeda Galaxy (a member of our Local Group)is moving away from us at a slower speed than Dr.Y believes.
C)Dr.X believes that the universe is older than Dr.Y believes.
D)Dr.X believes that the universe will someday stop expanding,while Dr.Y believes it will expand forever.
E)Dr.X believes that the universe has a much higher density than Dr.Y believes.

Question 27

Hubble's "constant" is constant in

A)time.
B)space.
C)space and time.
D)our Galaxy but different in others.

Question 28

Recall that Hubble's law is written v = H₀d,where v is the recession velocity of a galaxy located a distance d away from us,and H₀ is Hubble's constant.Suppose H₀ = 65 km/s/Mpc.How fast would a galaxy located 500 megaparsecs distant be receding from us?

A)65 km/s
B)65 Mpc/s
C)32,500 km/s
D)9 km/s
E)0.65 times the speed of light

Question 29

What is Hubble's law?

A)The longer the time period between peaks in brightness,the greater the luminosity of the Cepheid variable star.
B)The recession velocity of a galaxy is directly proportional to its distance from us.
C)The recession velocity of a galaxy is inversely proportional to its distance from us.
D)The faster a spiral galaxy's rotation speed,the more luminous it is.
E)The faster a spiral galaxy's rotation speed,the less luminous it is.

Question 30

Dr.Smith believes that the Hubble constant is H₀ = 70 km/s/Mpc.Dr.Jones believes it is H₀ = 50 km/s/Mpc.Which statement below automatically follows?

A)Dr.Smith believes that the universe is expanding,but Dr.Jones does not.
B)Dr.Smith believes that the Andromeda Galaxy (a member of our Local Group)is moving away from us at a faster speed than Dr.Jones believes.
C)Dr.Smith believes that the universe is older than Dr.Jones believes.
D)Dr.Smith believes that the universe is younger than Dr.Jones believes.
E)Dr.Smith believes that the universe will someday stop expanding,while Dr.Jones believes it will expand forever.

Question 31

White-dwarf supernovae are good standard candles for distance measurements for all the following reasons except which?

A)All white-dwarf supernovae involve the explosion of stars of nearly the same mass.
B)White-dwarf supernovae are so bright that they can be detected even in very distant galaxies.
C)White-dwarf supernovae are common enough that we detect several every year.
D)White-dwarf supernovae occur only among young and extremely bright stars.
E)All white-dwarf supernovae have similar light curves,which makes them easy to distinguish from massive-star supernovae.

Question 32

What makes white-dwarf supernovae good standard candles?

A)They are very bright,so they can be used to determine the distances to galaxies billions of light-years away.
B)They should all have approximately the same luminosity.
C)They occur so frequently that we can use them to measure the distances to virtually all galaxies.
D)We have had several occur close to us in the Milky Way,so we have been able to determine their luminosities very accurately.
E)both A and B

Question 33

What does the equivalent of an H-R diagram for galaxies,plotting luminosity versus color,show?

A)galaxies fill the diagram showing that there is no correlation between luminosity and color
B)two clumps,one blue with relatively low luminosity,one red with relatively high luminosity,and a valley in between with few galaxies
C)a continuum from faint,blue galaxies to bright,red galaxies
D)a continuum from faint,red galaxies to bright,blue galaxies
E)a main sequence,just as for stars

Question 34

What is the most accurate way to determine the distance to a very distant irregular galaxy?

A)using Cepheid variables
B)using a white-dwarf supernova as a standard candle
C)main sequence fitting
D)Hubble's law

Question 35

What is the most accurate way to determine the distance to a nearby galaxy?

A)radar ranging
B)stellar parallax
C)using Cepheid variables
D)Hubble's law

Question 36

Based on current estimates of the value of Hubble's constant,how old is the universe?

A)between 4 and 6 billion years old
B)between 8 and 12 billion years old
C)between 12 and 16 billion years old
D)between 16 and 20 billion years old
E)between 20 and 40 billion years old

Question 37

Why can't we see past the cosmological horizon?

A)The universe extends only to this horizon.
B)Beyond the cosmological horizon,we are looking back to a time before the universe had formed.
C)We do not have telescopes big enough.
D)We do not have sensitive enough detectors.
E)The cosmological horizon is infinitely far away,and we can't see to infinity.

Question 38

Which of the following sequences lists the methods for determining distance in the correct order from nearest to farthest?

A)parallax,Cepheid variables,Hubble's law
B)parallax,Hubble's law,Cepheid variables
C)parallax,white-dwarf supernovae,Hubble's law
D)parallax,Hubble's law,white-dwarf supernovae

Question 39

Why are galaxies in the blue cloud blue?

A)They contain hot,young stars that signify active star formation.
B)They are moving slower than stars in the red cloud.
C)They contain lots of dust that cause the bluish color.
D)They contain cold,dying stars that are fading to black.

Question 40

Spiral galaxies have more gas,dust,and younger stars than elliptical galaxies do.

Question 41

Elliptical galaxies are more likely to be found in clusters than are spiral galaxies.

Question 42

Based on the number of galaxies visible in the Hubble Deep Field (Figure 20.1 in your textbook),the estimated number of galaxies in our observable universe is

A)about 50,000.
B)about 100 million.
C)about 100 billion.
D)an infinite number.

Question 43

Explain why we observe distant galaxies to be moving away from us and therefore believe that the universe is expanding,but we don't see individual galaxies or clusters expanding.

Question 44

Briefly explain why we think white-dwarf supernovae are useful for measuring cosmic distances.

Question 45

Which of the following is not one of the three major categories of galaxies?

A)elliptical galaxies
B)globular galaxies
C)spiral galaxies
D)irregular galaxies

Question 46

All galaxies start out as members of the blue cloud,but some transition to the red sequence.

Question 47

How does the age of the universe depend on Hubble's constant,and why?

Question 48

A lenticular galaxy is another name for an elongated elliptical galaxy.

Question 49

There are more large spiral galaxies than there are large elliptical galaxies.

Question 50

Summarize the links in the distance chain that allow us to estimate distances to the farthest reaches of the universe.

Question 51

Recall that Hubble's law is written v = H₀d,where v is the recession velocity of a galaxy located a distance d away from us,and H₀ is Hubble's constant.Suppose H₀ = 55 km/s/Mpc.How fast would a galaxy located 500 megaparsecs distant be receding from us? Show all work clearly,and state your final answer with a complete sentence.Give the speed in units of kilometers per second and as a percentage of the speed of light.

Question 52

List at least three qualities that would tend to make a type of astronomical object useful as a standard candle.

Question 53

Process of Science: Most galaxies do not obey Hubble's Law perfectly.Why do we not take this as evidence that Hubble's law (and the theory of the expanding universe)is incorrect?

Question 54

Process of Science: How we can test that a so-called "standard candle" is indeed standard?

Question 55

Process of Science: Give examples of how we build upon our knowledge of stars to measure distances to the edge of the Universe.

Question 56

The larger the value of Hubble's constant,the more rapid the expansion of the universe and hence the younger the universe.

Question 57

Explain how we estimate that there are about 50-100 billion galaxies in the observable universe.

Question 58

If we were to measure Hubble's constant 10 billion years in the future,we would find it exactly the same as it is today.

Question 59

Process of Science: Describe how scientists measure the distances to galaxies,starting with how they measure the distances of the nearest stars.Be sure to include enough detail so that someone who does not know the jargon of astronomy can still understand your explanation.

Question 60

Massive-star supernovae and white-dwarf supernovae work equally well as standard candles for measuring cosmic distances.

Question 61

Overall,what is our most accurate technique for measuring the distance to a nearby star?

A)radar ranging
B)stellar parallax
C)Hubble's law
D)white dwarf supernovae

Question 62

Current estimates place the age of the universe at about

A)10 billion years.
B)10 million years.
C)14 billion years.
D)4 1/2 billion years.

Question 63

When we use an analogy that represents the expanding universe with the surface of an expanding balloon,what does the inside of the balloon represent?

A)It represents the center of the universe.
B)It represents the entire universe.
C)It represents regions of the universe beyond the Milky Way Galaxy.
D)The inside of the balloon does not represent any part of our universe.

Question 64

The most basic difference between elliptical galaxies and spiral galaxies is that

A)elliptical galaxies lack anything resembling the halo of a spiral galaxy.
B)elliptical galaxies have a spheroidal component (of stars distributed spherically about the galactic center),and spiral galaxies do not.
C)elliptical galaxies lack anything resembling the disk of a spiral galaxy.
D)elliptical galaxies are very old and spiral galaxies are very young.

Question 65

You observe the peak brightnesses of two white dwarf supernovae.Supernova A is only 1/4 as bright as Supernova B.What can you say about their relative distances?

A)Supernova A is twice as far away as Supernova B.
B)Supernova A is 4 times as far away as Supernova B.
C)Supernova B is 4 times as far away as Supernova A.
D)Supernova B is twice as far away as Supernova A.
E)We can't say anything about their relative distances because we do not have enough information.

Question 66

Which of the following best describes the status of the Milky Way in our Local Group of galaxies?

A)It is one of the two largest galaxies in the group.
B)It is one of about a dozen large spiral galaxies in the group.
C)It is by far the largest galaxy in the group.
D)It is quite average among the galaxies in the group.

Question 67

What does Hubble's law tell us?

A)The faster a spiral galaxy's rotation speed,the more luminous it is.
B)The longer the period of a Cepheid variable,the greater its luminosity.
C)For every force,there is an equal and opposite reaction force.
D)The more distant a galaxy,the faster it is moving away from us.

Question 68

If we say that a galaxy has a lookback time of 1 billion years,we mean that

A)its light traveled through space for 1 billion years to reach us.
B)is now 1 billion light-years away.
C)it was 1 billion light-years away when the light left the galaxy.
D)it is 400 million years old.

Question 69

The fact that the universe is expanding means that space itself is growing within

A)the Milky Way.
B)clusters of galaxies.
C)the observable universe.
D)the Local Group.

Question 70

Given that white dwarf supernovae are such good standard candles,why don't we use them to measure the distance to all galaxies?

A)They are rare events,so we have observed them in only a tiny fraction of all galaxies.
B)We cannot see them beyond a distance of about 100 million light-years.
C)They can occur only in spiral galaxies,not elliptical galaxies.
D)We would,but we don't have enough telescopes.

Question 71

Galaxies with disks but no evident spiral arms are called

A)irregular galaxies.
B)lenticular galaxies.
C)barred spiral galaxies.
D)spheroidal components.

Question 72

In a photo like the Hubble Deep Field (Figure 20.1 in your textbook),we see galaxies in many different stages of their lives.In general,which galaxies are seen in the earliest (youngest)stages of their lives?

A)the galaxies that are farthest away
B)the galaxies that have the most hot,young O and B stars
C)the galaxies that are the reddest in color
D)the galaxies that are nearest to us

Question 73

Which of the following statements about types of galaxies is not true?

A)Spiral galaxies have younger stars than elliptical galaxies.
B)Among the large galaxies in the universe outside of clusters,most are spiral.
C)Large elliptical galaxies are more common in clusters of galaxies than they are outside of clusters.
D)Elliptical galaxies are bluer and contain more dust than spiral galaxies.

Question 74

A standard candle is

A)a 7-cm-long wax candle.
B)another name for a main-sequence star.
C)another name for a barred-spiral galaxy.
D)a light source of known luminosity.

Question 75

Hubble's galaxy classification diagram (the "tuning fork")

A)explains active galactic nuclei.
B)shows how galaxies evolve from one form to another.
C)suggests the existence of black holes.
D)relates galaxies according to their shapes,but not according to any evolutionary status.

Question 76

Although the entire universe may be much larger than our observable universe,we can see only within our observable universe.The "boundary" of our observable universe is called

A)the cosmological horizon.
B)the Big Bang.
C)the lookback time.
D)the singularity.

Question 77

What two observable properties of a Cepheid variable are directly related to one another?

A)the period between its peaks of brightness and its distance
B)its luminosity and its mass
C)the period between its peaks of brightness and its luminosity
D)its mass and its distance

Question 78

Cosmological redshift is the result of

A)the high speeds at which galaxies move within clusters.
B)the expansion of the universe.
C)very old,red stars in distant galaxies.
D)supermassive black holes.

Question 79

What is a Cepheid variable?

A)It is a bright source of variable X-ray emission,thought to harbor a supermassive black hole.
B)It is a type of very luminous star that makes an excellent standard candle.
C)It is a main-sequence star of spectral type B5.
D)It is a type of galaxy that varies in its light output.

Question 80

Spectral lines from Galaxy B are redshifted from their rest wavelengths twice as much as the spectral lines from Galaxy A.According to Hubble's law,what can you say about their approximate relative distances?

A)Galaxy A is twice as far as Galaxy B.
B)Galaxy B is four times as far as Galaxy A.
C)Galaxy A is four times as far as Galaxy B.
D)Galaxy B is twice as far as Galaxy A.
E)Not enough information to say-you need to know Hubble's constant to answer this question.