Question 1

Elliptical galaxies appear red because:

Accepted Answer

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 
E)  they contain a mix of old and young stars 
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 
E)  they contain a mix of old and young stars

Question 2

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

Accepted Answer

Elliptical and spiral galaxies are organ

Question 3

Dust in galaxies does not count as dark matter because:

Accepted Answer

A)  it only absorbs some wavelengths of light but not all wavelengths the way dark matter does 
B)  it interacts with light 
C)  it is only found in spiral disks, whereas dark matter is more widely distributed 
D)  dust is easily destroyed by dark matter 
E)  there is never enough to make all the gravity 
A)  it only absorbs some wavelengths of light but not all wavelengths the way dark matter does 
B)  it interacts with light 
C)  it is only found in spiral disks, whereas dark matter is more widely distributed 
D)  dust is easily destroyed by dark matter 
E)  there is never enough to make all the gravity

Question 4

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

Accepted Answer

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 approximately constant at distances well beyond the visible edges of galaxies, implying that galaxies contain much more matter than what we observe in stars and gas. 
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. 
E)  The velocity of stars falls slowly in the outer regions of galaxies, showing that while there is a lot of dark matter it is distributed the same way as is the visible light. 
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 approximately constant at distances well beyond the visible edges of galaxies, implying that galaxies contain much more matter than what we observe in stars and gas. 
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. 
E)  The velocity of stars falls slowly in the outer regions of galaxies, showing that while there is a lot of dark matter it is distributed the same way as is the visible light.

Question 5

If you measure the velocity of a cloud of gas that is rotating around the center of a galaxy in a circular orbit with radius R, you can determine:

Accepted Answer

A)  the total mass of the galaxy 
B)  the mass of the stars and gas in the galaxy 
C)  the mass of the galaxy enclosed within the radius R 
D)  the mass of the galaxy located outside the radius R 
E)  the mass of luminous matter within the radius R 
A)  the total mass of the galaxy 
B)  the mass of the stars and gas in the galaxy 
C)  the mass of the galaxy enclosed within the radius R 
D)  the mass of the galaxy located outside the radius R 
E)  the mass of luminous matter within the radius R

Question 6

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

Accepted Answer

The most likely source of the

Question 7

We classify galaxies by:

Accepted Answer

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

Question 8

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

Accepted Answer

A)  They measured the velocities of stars in the inner regions of 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. 
E)  They measured X-ray emission from hot gas gravitationally bound to the galaxies. 
A)  They measured the velocities of stars in the inner regions of 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. 
E)  They measured X-ray emission from hot gas gravitationally bound to the galaxies.

Question 9

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

Accepted Answer

A)  3 percent 
B)  15 percent 
C)  20 percent 
D)  50 percent 
E)  80 percent 
A)  3 percent 
B)  15 percent 
C)  20 percent 
D)  50 percent 
E)  80 percent

Question 10

If the rotational speed of the gas in the disk of a spiral galaxy is 200 km/s at a distance of 25,000 pc from its center, then what is the mass enclosed within this radius?

Accepted Answer

A)  7.5 billion M $\odot$ 
B)  18 billion M $\odot$ 
C)  70 billion M $\odot$ 
D)  230 billion M $\odot$ 
E)  400 billion M $\odot$ 
A)  7.5 billion M $\odot$ 
B)  18 billion M $\odot$ 
C)  70 billion M $\odot$ 
D)  230 billion M $\odot$ 
E)  400 billion M $\odot$

Question 11

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

Accepted Answer

AGNs have been observed to vary dramatic

Question 12

We know AGN are about the size of our Solar System because of how fast they change in brightness over time.

Accepted Answer

A) True 
 B)False

Question 13

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

Accepted Answer

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. 
E)  They both demonstrate the existence of dark matter. 
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. 
E)  They both demonstrate the existence of dark matter.

Question 14

If there is a 2 million M $\odot$  black hole at the center of our galaxy, why is our own galaxy not an AGN?

Accepted Answer

There is currently n

Question 15

You observe a quasar that varies in brightness over a period of 50 days as shown in the figure below. Using these data, estimate the size of the AGN region in AU.

Accepted Answer

A)  20 AU 
B)  100 AU 
C)  500 AU 
D)  3,500 AU 
E)  10,000 AU 
A)  20 AU 
B)  100 AU 
C)  500 AU 
D)  3,500 AU 
E)  10,000 AU

Elliptical galaxies appear red because:

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

Dust in galaxies does not count as dark matter because:

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

If you measure the velocity of a cloud of gas that is rotating around the center of a galaxy in a circular orbit with radius R, you can determine:

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

We classify galaxies by:

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

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

If the rotational speed of the gas in the disk of a spiral galaxy is 200 km/s at a distance of 25,000 pc from its center, then what is the mass enclosed within this radius?

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

We know AGN are about the size of our Solar System because of how fast they change in brightness over time.

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

If there is a 2 million M _$\odot$ black hole at the center of our galaxy, why is our own galaxy not an AGN?

You observe a quasar that varies in brightness over a period of 50 days as shown in the figure below. Using these data, estimate the size of the AGN region in AU.

Why Learn Astronomy

Patterns in the Skymotions of Earth

Motion of Astronomical Bodies

Gravity and Orbits

Light

The Tools of the Astronomer

The Birth and Evolution of Planetary Systems

The Terrestrial Planets and Earths Moon

Atmospheres of the Terrestrial Planets

Worlds of Gas and Liquid the Giant Planets

Planetary Adornmentsmoons and Rings

Dwarf Planets and Small Solar System Bodies

Taking the Measure of Stars

Our Starthe Sun

Star Formation and the Interstellar Medium

Evolution of Low-Mass Stars

Evolution of High-Mass Stars

Relativity and Black Holes

The Expanding Universe

The Milky Waya Normal Spiral Galaxy

Modern Cosmology

Large-Scale Structure in the Universe

Life

Filters

Exam 20: Galaxies

Elliptical galaxies appear red because:

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

Dust in galaxies does not count as dark matter because:

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

If you measure the velocity of a cloud of gas that is rotating around the center of a galaxy in a circular orbit with radius R, you can determine:

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

We classify galaxies by:

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

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

If the rotational speed of the gas in the disk of a spiral galaxy is 200 km/s at a distance of 25,000 pc from its center, then what is the mass enclosed within this radius?

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

We know AGN are about the size of our Solar System because of how fast they change in brightness over time.

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

If there is a 2 million M ⊙\odot⊙ black hole at the center of our galaxy, why is our own galaxy not an AGN?

You observe a quasar that varies in brightness over a period of 50 days as shown in the figure below. Using these data, estimate the size of the AGN region in AU.

Why Learn Astronomy

Patterns in the Skymotions of Earth

Motion of Astronomical Bodies

Gravity and Orbits

Light

The Tools of the Astronomer

The Birth and Evolution of Planetary Systems

The Terrestrial Planets and Earths Moon

Atmospheres of the Terrestrial Planets

Worlds of Gas and Liquid the Giant Planets

Planetary Adornmentsmoons and Rings

Dwarf Planets and Small Solar System Bodies

Taking the Measure of Stars

Our Starthe Sun

Star Formation and the Interstellar Medium

Evolution of Low-Mass Stars

Evolution of High-Mass Stars

Relativity and Black Holes

The Expanding Universe

The Milky Waya Normal Spiral Galaxy

Modern Cosmology

Large-Scale Structure in the Universe

Life

Filters

If there is a 2 million M _$\odot$ black hole at the center of our galaxy, why is our own galaxy not an AGN?