Question 1

How do mass-to-light ratios for the inner regions of galaxies compare to the mass-to-light ratios we find when we look farther from a galaxy's center? What does this tell us about dark matter in galaxies?

Accepted Answer

The farther we look from a galaxy's cent...

Question 2

What do we mean by the critical density of the universe?

Accepted Answer

In the absence of any mysterious repulsi...

Question 3

It is more difficult to determine the total amount of dark matter in an elliptical galaxy than in a spiral galaxy.Why?

Accepted Answer

A)  Elliptical galaxies lack the atomic hydrogen gas that we use to determine orbital speeds at great distances from the centers of spiral galaxies.
B)  Elliptical galaxies contain much less dark matter than spiral galaxies,so it's much more difficult to measure.
C)  Stars in elliptical galaxies are dimmer,making them harder to study.
D)  cannot observe spectral lines for elliptical galaxies.E) None of the above
F) All of the above

Question 4

The only possible geometry of an accelerating universe is open.

Accepted Answer

A) True 
 B)False

Question 5

Which of the following statements best summarizes current evidence concerning dark matter in individual galaxies and in clusters of galaxies?

Accepted Answer

A)  Dark matter is the dominant form of mass in both clusters and in individual galaxies.
B)  Dark matter is present between galaxies in clusters,but not within individual galaxies.
C)  Dark matter is present in individual galaxies,but there is no evidence that it can exist between the galaxies in a cluster.
D)  Within individual galaxies,dark matter is always concentrated near the galactic center,and within clusters it is always concentrated near the cluster center.E) None of the above
F) B) and C)

Question 6

Which of the following best sums up current scientific thinking about the nature of dark energy?

Accepted Answer

A)  Dark energy most likely consists of a form of photons that we can't see or detect.
B)  Dark energy is most likely made up of weakly interacting particles that do not interact with light.
C)  Dark energy probably exists,but we have little (if any) idea what it is.
D)  Dark energy is the source of the mind weapon used by Sith Lords in Star Wars.E) A) and C)
F) A) and B)

Question 7

Compared to the central regions of spiral galaxies,we expect elliptical galaxies to have

Accepted Answer

A)  higher mass-to-light ratios because stars in elliptical galaxies are dimmer than those in spirals.
B)  lower mass-to-light ratios because stars in elliptical galaxies are dimmer than those in spirals.
C)  higher mass-to-light ratios because stars in elliptical galaxies do not have high orbital velocities.
D)  lower mass-to-light ratios because elliptical galaxies have less gas and dust than spirals.
E)  the same mass-to-light ratio because they are made of the same material,stars and dark matter.F) A) and E)
G) A) and D)

Question 8

Briefly explain how dark matter affects the expansion rate of the universe and the significance of the term critical density in the absence of any mysterious repulsive force.

Accepted Answer

Dark matter slows the expansion of the u...

Question 9

Imagine that it turns out that dark matter (not dark energy) is made up of an unstable form of matter that decays into photons or other forms of energy about 50 billion years from now.Based on current understanding,how would that affect the universe at that time?

Accepted Answer

A)  Stars would cease to exist when the dark matter is gone.
B)  Planetary systems would expand and disperse.
C)  The galaxies in clusters would begin to fly apart.
D)  The universe would cease its expansion.E) All of the above
F) A) and C)

Question 10

Process of Science: Evidence for dark matter in galaxy clusters can be seen in observations of the motions of individual galaxies,X-ray observations of hot intra-cluster gas,and gravitational lensing.What is different about lensing that further strengthens the case that dark matter really does exist.

Accepted Answer

Gravitational lensing provides a mass es...

Question 11

How does gravitational lensing tell us about the mass of a galaxy cluster?

Accepted Answer

A)  The lensing allows us to determine the orbital speeds of galaxies in the cluster,so that we can determine the mass of the cluster from the orbital velocity law.
B)  The lensing broadens spectral lines,and we can use the broadening to "weigh" the cluster.
C)  Using Einstein's general theory of relativity,we can calculate the cluster's mass from the precise way in which it distorts the light of galaxies behind it.
D)  Newton's universal law of gravitation predicts how mass can distort light,so we can apply Newton's law to determine the mass of the cluster.E) None of the above
F) All of the above

Question 12

Which of the following best summarizes what we mean by dark matter?

Accepted Answer

A)  matter that we have identified from its gravitational effects but that we cannot see in any wavelength of light
B)  matter that may inhabit dark areas of the cosmos where we see nothing at all
C)  matter consisting of black holes
D)  matter for which we have theoretical reason to think it exists,but no observational evidence for its existenceE) A) and C)
F) All of the above

Question 13

Based on current evidence,a supercluster is most likely to have formed in regions of space where

Accepted Answer

A)  the density of dark matter was slightly higher than average when the universe was very young.
B)  there was an excess concentration of hydrogen gas when the universe was very young.
C)  supermassive black holes were present in the very early universe.
D)  the acceleration of the expansion was proceeding faster than elsewhere.E) C) and D)
F) B) and C)

Question 14

When we say that a cluster of galaxies is acting as a gravitational lens,what do we mean?

Accepted Answer

A)  It magnifies the effects of gravity that we see in the cluster.
B)  It is an unusually large cluster that has a lot of gravity.
C)  It bends or distorts the light coming from galaxies located behind it.
D)  The overall shape of the cluster is that of a lens.E) A) and B)
F) None of the above

Question 15

What do we mean when we say that a particle is a weakly interacting particle?

Accepted Answer

A)  It interacts only through the weak force.
B)  It interacts only through the weak force and the force of gravity.
C)  It is so small that it doesn't affect objects in the universe.
D)  It doesn't interact with any type of baryonic matter.
E)  It is the only type of particle that interacts through the weak force.F) None of the above
G) A) and B)

Question 16

What does the universe look like on very large scales?

Accepted Answer

A)  Galaxies are uniformly distributed.
B)  Galaxies are randomly distributed.
C)  Galaxies are distributed in a hierarchy of clusters,superclusters,and hyperclusters.
D)  Galaxies appear to be distributed in chains and sheets that surround great voids.
E)  Galaxies are distributed in a great shell expanding outward from the center of the universe.F) A) and B)
G) A) and E)

Question 17

Our universe will end in a big crunch.

Accepted Answer

A) True 
 B)False

Question 18

What is the distinguishing characteristic of what we call ordinary or baryonic matter?

Accepted Answer

A)  It emits a great deal of light.
B)  It can attract other matter through the force of gravity.
C)  It is made of subatomic particles that scientists call WIMPs.
D)  It consists of atoms or ions with nuclei made from protons and neutrons.E) B) and D)
F) A) and B)

Question 19

Based on current evidence concerning the amount of deuterium in the universe,we can conclude that

Accepted Answer

A)  ordinary (baryonic) matter makes up most of the mass of the universe.
B)  neutrons greatly outnumber protons in the universe.
C)  most of the deuterium that was created during the era of nucleosynthesis has since been destroyed.
D)  the density of ordinary (baryonic) matter is between 1 percent and 10 percent of the critical density.
E)  we live in a critical-density universe.F) A) and C)
G) B) and E)

Question 20

Briefly describe two different ways of measuring the mass of a cluster of galaxies.

Accepted Answer

There are three basic methods: The first...

Exam 23: Dark Matter, Dark Energy, and the Fate of the Universe

Our universe will end in a big crunch.

Correct Answer
verified

What do we mean when we say that a particle is a weakly interacting particle?

Correct Answer
verified

When we say that a cluster of galaxies is acting as a gravitational lens,what do we mean?

Correct Answer
verified

What does the universe look like on very large scales?

Correct Answer
verified

Correct Answer
verified
Gravitational lensing provides a mass es...
View Answer

What is the distinguishing characteristic of what we call ordinary or baryonic matter?

Correct Answer
verified

How do mass-to-light ratios for the inner regions of galaxies compare to the mass-to-light ratios we find when we look farther from a galaxy's center? What does this tell us about dark matter in galaxies?

Correct Answer
verified
The farther we look from a galaxy's cent...
View Answer

Compared to the central regions of spiral galaxies,we expect elliptical galaxies to have

Correct Answer
verified

Based on current evidence,a supercluster is most likely to have formed in regions of space where

Correct Answer
verified

Briefly describe two different ways of measuring the mass of a cluster of galaxies.

Correct Answer
verified
There are three basic methods: The first...
View Answer

Imagine that it turns out that dark matter (not dark energy) is made up of an unstable form of matter that decays into photons or other forms of energy about 50 billion years from now.Based on current understanding,how would that affect the universe at that time?

Correct Answer
verified

Which of the following best summarizes what we mean by dark matter?

Correct Answer
verified

Briefly explain how dark matter affects the expansion rate of the universe and the significance of the term critical density in the absence of any mysterious repulsive force.

Correct Answer
verified
Dark matter slows the expansion of the u...
View Answer

Which of the following best sums up current scientific thinking about the nature of dark energy?

Correct Answer
verified

How does gravitational lensing tell us about the mass of a galaxy cluster?

Correct Answer
verified

It is more difficult to determine the total amount of dark matter in an elliptical galaxy than in a spiral galaxy.Why?

Correct Answer
verified

What do we mean by the critical density of the universe?

Correct Answer
verified
In the absence of any mysterious repulsi...
View Answer

The only possible geometry of an accelerating universe is open.

Correct Answer
verified

Which of the following statements best summarizes current evidence concerning dark matter in individual galaxies and in clusters of galaxies?

Correct Answer
verified

Based on current evidence concerning the amount of deuterium in the universe,we can conclude that

Correct Answer
verified

Exam 23: Dark Matter, Dark Energy, and the Fate of the Universe

Our universe will end in a big crunch.

Correct AnswerverifiedShow Answer

What do we mean when we say that a particle is a weakly interacting particle?

Correct AnswerverifiedShow Answer

When we say that a cluster of galaxies is acting as a gravitational lens,what do we mean?

Correct AnswerverifiedShow Answer

What does the universe look like on very large scales?

Correct AnswerverifiedShow Answer

Correct AnswerverifiedGravitational lensing provides a mass es...View AnswerShow Answer

What is the distinguishing characteristic of what we call ordinary or baryonic matter?

Correct AnswerverifiedShow Answer

How do mass-to-light ratios for the inner regions of galaxies compare to the mass-to-light ratios we find when we look farther from a galaxy's center? What does this tell us about dark matter in galaxies?

Correct AnswerverifiedThe farther we look from a galaxy's cent...View AnswerShow Answer

Compared to the central regions of spiral galaxies,we expect elliptical galaxies to have

Correct AnswerverifiedShow Answer

Based on current evidence,a supercluster is most likely to have formed in regions of space where

Correct AnswerverifiedShow Answer

Briefly describe two different ways of measuring the mass of a cluster of galaxies.

Correct AnswerverifiedThere are three basic methods: The first...View AnswerShow Answer

Imagine that it turns out that dark matter (not dark energy) is made up of an unstable form of matter that decays into photons or other forms of energy about 50 billion years from now.Based on current understanding,how would that affect the universe at that time?

Correct AnswerverifiedShow Answer

Which of the following best summarizes what we mean by dark matter?

Correct AnswerverifiedShow Answer

Briefly explain how dark matter affects the expansion rate of the universe and the significance of the term critical density in the absence of any mysterious repulsive force.

Correct AnswerverifiedDark matter slows the expansion of the u...View AnswerShow Answer

Which of the following best sums up current scientific thinking about the nature of dark energy?

Correct AnswerverifiedShow Answer

How does gravitational lensing tell us about the mass of a galaxy cluster?

Correct AnswerverifiedShow Answer

It is more difficult to determine the total amount of dark matter in an elliptical galaxy than in a spiral galaxy.Why?

Correct AnswerverifiedShow Answer

What do we mean by the critical density of the universe?

Correct AnswerverifiedIn the absence of any mysterious repulsi...View AnswerShow Answer

The only possible geometry of an accelerating universe is open.

Correct AnswerverifiedShow Answer

Which of the following statements best summarizes current evidence concerning dark matter in individual galaxies and in clusters of galaxies?

Correct AnswerverifiedShow Answer

Based on current evidence concerning the amount of deuterium in the universe,we can conclude that

Correct AnswerverifiedShow Answer

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified
Gravitational lensing provides a mass es...
View Answer

Correct Answer
verified

Correct Answer
verified
The farther we look from a galaxy's cent...
View Answer

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified
There are three basic methods: The first...
View Answer

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified
Dark matter slows the expansion of the u...
View Answer

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified
In the absence of any mysterious repulsi...
View Answer

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified