Question 1

Which of the following statements about galaxies is true?

Accepted Answer

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 2

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?

Accepted Answer

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.

Question 3

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

Accepted Answer

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

Question 4

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

Accepted Answer

The answer of How does the age of the universe...

Question 5

Given that the universe is about 14 billion years old,which of the following statements is logically valid?

Accepted Answer

A) All galaxies nearby us are about 14 billion years old. 
B) All galaxies that we can see are about 14 billion years old. 
C) All galaxies that we see have an age that is approximately equal to the age of the universe today,minus the lookback time (or light travel time)corresponding to the redshift of that galaxy. 
D) The oldest galaxies we see at great distances are younger than the oldest galaxies we see nearby.

Question 6

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

Accepted Answer

A) True 
 B)False

Question 7

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

Accepted Answer

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 8

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

Accepted Answer

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

Question 9

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

Accepted Answer

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

Question 10

What is a Cepheid variable?

Accepted Answer

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 11

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?

Accepted Answer

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 12

Hubble's constant is about 22 km/s/million light-years,implying an age of about 14 billion years for the universe.If Hubble's constant were 11 km/s/million light-years,the age of the universe would be about

Accepted Answer

A) 7 billion years. 
B) 14 billion years. 
C) 28 billion years. 
D) Impossible to say,because Hubble's constant has no relationship to the age of the universe.

Question 13

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.

Accepted Answer

The answer of Recall that Hubble's law is written v...

Question 14

Why can't we see past the cosmological horizon?

Accepted Answer

A) Beyond the cosmological horizon,we would be looking back to a time before the universe was born. 
B) We do not have big enough telescopes. 
C) The cosmological horizon is infinitely far away,and we can't see to infinity. 
D) Every galaxy in the entire universe (not just the observable universe)exists within the cosmological horizon,so there's nothing to see beyond it.

Question 15

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.

Accepted Answer

A) True 
 B)False

Question 16

Suppose that Hubble's constant were 20 kilometers per second per million light-years.How fast would we expect a galaxy 100 million light-years away to be moving? (Assume the motion is due only to Hubble's law. )

Accepted Answer

A) away from us at 200 km/s 
B) toward us at 2,000 km/s 
C) away from us at 2,000 km/s 
D) away from us at 20,000 km/s

Question 17

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

Accepted Answer

The answer of List at least three qualities that would...

Question 18

Galaxies with disks but no evident spiral arms are called

Accepted Answer

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

Question 19

Hubble's "constant" is constant in

Accepted Answer

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

Question 20

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

Accepted Answer

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.

Exam 20: Galaxies and the Foundations of Modern Cosmology