Question 1

How do we measure directly that AGNs have black holes at their centers?

Accepted Answer

A)  We know that massive stars make black holes, and most galaxies contain a lot of massive stars. 
B)  We know black holes are made of dark matter, and galaxies are mostly made up of dark matter. 
C)  We know that black holes emit radio waves, and many AGNs are bright at radio waves. 
D)  We measure that the mass of the black hole is increasing as material falls into it. 
E)  In some systems, we can see both redshifted and blueshifted emission lines from material orbiting around the black hole. 
A)  We know that massive stars make black holes, and most galaxies contain a lot of massive stars. 
B)  We know black holes are made of dark matter, and galaxies are mostly made up of dark matter. 
C)  We know that black holes emit radio waves, and many AGNs are bright at radio waves. 
D)  We measure that the mass of the black hole is increasing as material falls into it. 
E)  In some systems, we can see both redshifted and blueshifted emission lines from material orbiting around the black hole.

Question 2

If you observed a gas cloud orbiting in a disk of a spiral galaxy that was located 10,000 pc from the center and it rotated with a speed of 300 km/s, what is the mass of the galaxy interior to gas cloud's orbit?

Accepted Answer

A)  1 * 1011 M $\odot$ 
B)  2 * 1011 M $\odot$ 
C)  8 *1011 M $\odot$ 
D)  1 * 1012 M $\odot$ 
E)  4 * 1012 M $\odot$ 
A)  1 * 1011 M $\odot$ 
B)  2 * 1011 M $\odot$ 
C)  8 *1011 M $\odot$ 
D)  1 * 1012 M $\odot$ 
E)  4 * 1012 M $\odot$

Question 3

If the rotational speed of the gas in the disk of a spiral galaxy is 100 km/s at a distance of 26,000 light-years from its center, then what is the mass enclosed within this radius? If the mass of luminous matter inside this radius is 5 billion M $\odot$  then what fraction of the galaxy's mass is made of dark matter?

Accepted Answer

The radius of the gas is:
r=26,000 ly =

Question 4

Today in our local universe, approximately 30 percent of galaxies are AGNs.

Accepted Answer

A) True 
 B)False

Question 5

We interpret the fact that we saw more AGNs in the past than we do today to indicate that:

Accepted Answer

A)  there were fewer galaxy-galaxy interactions in the past 
B)  there were more galaxy-galaxy interactions in the past 
C)  supermassive black holes were larger in the past 
D)  today's AGNs are primarily hidden by large amounts of cold gas and dust 
E)  AGNs had bigger central black holes in the past 
A)  there were fewer galaxy-galaxy interactions in the past 
B)  there were more galaxy-galaxy interactions in the past 
C)  supermassive black holes were larger in the past 
D)  today's AGNs are primarily hidden by large amounts of cold gas and dust 
E)  AGNs had bigger central black holes in the past

Question 6

The image below was probably taken in ____________ wavelengths because _______________________.

Accepted Answer

A)  radio; the disk probably contains many planets with intelligent life, who are beaming out radio and television signals into space 
B)  infrared; the central regions are bright, and cool stars in the bulges emit a lot of infrared light 
C)  visible; there is a lot dust in this galaxy that blocks light in a ring about halfway along the disk 
D)  ultraviolet; the light from hot young stars is mainly found along spiral arms 
E)  X-ray; the central nucleus is easily seen, and AGN emit a lot of X-rays 
A)  radio; the disk probably contains many planets with intelligent life, who are beaming out radio and television signals into space 
B)  infrared; the central regions are bright, and cool stars in the bulges emit a lot of infrared light 
C)  visible; there is a lot dust in this galaxy that blocks light in a ring about halfway along the disk 
D)  ultraviolet; the light from hot young stars is mainly found along spiral arms 
E)  X-ray; the central nucleus is easily seen, and AGN emit a lot of X-rays

Question 7

Spiral structure:

Accepted Answer

A)  rotates at the same speed as the gas in the disk 
B)  rotates at a speed that is different than the gas in the disk 
C)  stays constant in time as the gas in disk rotates through it 
D)  rotates backward compared to the stellar orbits 
E)  must only last a short time, since few galaxies with disks show spiral patterns 
A)  rotates at the same speed as the gas in the disk 
B)  rotates at a speed that is different than the gas in the disk 
C)  stays constant in time as the gas in disk rotates through it 
D)  rotates backward compared to the stellar orbits 
E)  must only last a short time, since few galaxies with disks show spiral patterns

Question 8

Two elliptical galaxies have the same apparent size and brightness. Galaxy A appears lumpy, and it is possible to observe individual stars and star clusters. The other one, galaxy B, appears very smooth, with no fine detail. Which one is likely to be more luminous?

Accepted Answer

A)  Galaxy A. It has to contain more luminous objects if we can see them individually, and so the galaxy as a whole has to be more luminous. 
B)  Galaxy A. The lumpiness means that there is a lot of dust in the galaxy, which absorbs some of the starlight. Therefore the total amount actually emitted must be larger, if it is to have the same brightness as the other galaxy. 
C)  Neither. If they have the same apparent size and brightness, they must be at equal distances. 
D)  Galaxy B. This galaxy appears smooth because it is farther away and the light from its stars all blends together. Because it is farther away, it has to be more luminous. 
E)  Galaxy B. The smooth light distribution means that the stars are moving around very quickly. Therefore the galaxy has more mass and is more luminous. 
A)  Galaxy A. It has to contain more luminous objects if we can see them individually, and so the galaxy as a whole has to be more luminous. 
B)  Galaxy A. The lumpiness means that there is a lot of dust in the galaxy, which absorbs some of the starlight. Therefore the total amount actually emitted must be larger, if it is to have the same brightness as the other galaxy. 
C)  Neither. If they have the same apparent size and brightness, they must be at equal distances. 
D)  Galaxy B. This galaxy appears smooth because it is farther away and the light from its stars all blends together. Because it is farther away, it has to be more luminous. 
E)  Galaxy B. The smooth light distribution means that the stars are moving around very quickly. Therefore the galaxy has more mass and is more luminous.

Question 9

We know that spiral galaxies contain dark matter because the gas in the disk rotates with a velocity that decreases in a way that is proportional to r -1/2.

Accepted Answer

A) True 
 B)False

Question 10

What do the broad emission lines in quasar spectra tell astronomers about these objects?

Accepted Answer

A)  They are very far away. 
B)  They are moving away from us. 
C)  They have rapid internal motions. 
D)  They are very dense. 
E)  They have few heavy elements. 
A)  They are very far away. 
B)  They are moving away from us. 
C)  They have rapid internal motions. 
D)  They are very dense. 
E)  They have few heavy elements.

Question 11

The type of AGN we see depends mostly on the angle at which we view the galaxy.

Accepted Answer

A) True 
 B)False

Question 12

The Hubble tuning fork diagram represents an evolutionary diagram of galaxies from elliptical to spiral.

Accepted Answer

A) True 
 B)False

Question 13

In spiral galaxies, the size of the central bulge is correlated with the:

Accepted Answer

A)  tightness of the spiral arms 
B)  luminosity of the galaxy 
C)  age of the galaxy 
D)  thickness of the disk 
E)  presence of an active nucleus 
A)  tightness of the spiral arms 
B)  luminosity of the galaxy 
C)  age of the galaxy 
D)  thickness of the disk 
E)  presence of an active nucleus

Question 14

What are the main components of an AGN?

Accepted Answer

All AGN of any luminosity cons

Question 15

How do we know that AGNs have sizes on the order of our Solar System?

Accepted Answer

A)  Quasars and Seyfert galaxies are stellar-like sources. 
B)  Their brightness varies by factors of a few. 
C)  The emission lines in their spectra show gas rotating at speeds of thousands of km/s. 
D)  Their brightness varies on timescales ranging from hours to a day. 
E)  We can measure their angular size, which gives us the physical size when we know the distance. 
A)  Quasars and Seyfert galaxies are stellar-like sources. 
B)  Their brightness varies by factors of a few. 
C)  The emission lines in their spectra show gas rotating at speeds of thousands of km/s. 
D)  Their brightness varies on timescales ranging from hours to a day. 
E)  We can measure their angular size, which gives us the physical size when we know the distance.

Question 16

Dark matter consists of material that emits radiation at wavelengths other than visible light.

Accepted Answer

A) True 
 B)False

Question 17

Long-lasting spiral density waves occur in the disk of a spiral galaxy when:

Accepted Answer

A)  the spiral merges with another galaxy 
B)  the galaxy is young 
C)  the galaxy's disk is regularly disturbed 
D)  the galaxy absorbs a satellite galaxy 
E)  a supernova explosion takes place 
A)  the spiral merges with another galaxy 
B)  the galaxy is young 
C)  the galaxy's disk is regularly disturbed 
D)  the galaxy absorbs a satellite galaxy 
E)  a supernova explosion takes place

Question 18

Give three examples of types of active galactic nuclei and give one reason why each is unique.

Accepted Answer

Three types of AGNs: (1) quasars-extreme

Question 19

Roughly what percentage of the total mass of a galaxy is made up of luminous, or normal, matter?

Accepted Answer

A)  5 percent 
B)  25 percent 
C)  33 percent 
D)  50 percent 
E)  90 percent 
A)  5 percent 
B)  25 percent 
C)  33 percent 
D)  50 percent 
E)  90 percent

Question 20

Stars in elliptical galaxies have velocities that:

Accepted Answer

A)  change constantly 
B)  are very large in size 
C)  are equal in all directions 
D)  are constant in time 
E)  are orientated in random in directions 
A)  change constantly 
B)  are very large in size 
C)  are equal in all directions 
D)  are constant in time 
E)  are orientated in random in directions

Exam 20: Galaxies

How do we measure directly that AGNs have black holes at their centers?

If you observed a gas cloud orbiting in a disk of a spiral galaxy that was located 10,000 pc from the center and it rotated with a speed of 300 km/s, what is the mass of the galaxy interior to gas cloud's orbit?

Today in our local universe, approximately 30 percent of galaxies are AGNs.

We interpret the fact that we saw more AGNs in the past than we do today to indicate that:

The image below was probably taken in ____________ wavelengths because _______________________.

Spiral structure:

Two elliptical galaxies have the same apparent size and brightness. Galaxy A appears lumpy, and it is possible to observe individual stars and star clusters. The other one, galaxy B, appears very smooth, with no fine detail. Which one is likely to be more luminous?

We know that spiral galaxies contain dark matter because the gas in the disk rotates with a velocity that decreases in a way that is proportional to r -1/2.

What do the broad emission lines in quasar spectra tell astronomers about these objects?

The type of AGN we see depends mostly on the angle at which we view the galaxy.

The Hubble tuning fork diagram represents an evolutionary diagram of galaxies from elliptical to spiral.

In spiral galaxies, the size of the central bulge is correlated with the:

What are the main components of an AGN?

How do we know that AGNs have sizes on the order of our Solar System?

Dark matter consists of material that emits radiation at wavelengths other than visible light.

Long-lasting spiral density waves occur in the disk of a spiral galaxy when:

Give three examples of types of active galactic nuclei and give one reason why each is unique.

Roughly what percentage of the total mass of a galaxy is made up of luminous, or normal, matter?

Stars in elliptical galaxies have velocities that:

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

The image below was probably taken in wavelengths because ___________.

We know that spiral galaxies contain dark matter because the gas in the disk rotates with a velocity that decreases in a way that is proportional to r ^-^1/2.