Question 1

Seyfert galaxies are unique because they have large lobes of radio emission that extend well beyond the visible part of the galaxy.

Accepted Answer

A) True 
 B)False

Question 2

Assume that when a supermassive black hole accretes gas,approximately 50 percent of its mass is converted directly into energy,which is radiated away.If a quasar has a luminosity of 1014 L⨀ then what must its mass accretion rate be?

Accepted Answer

A) 1 M⨀ per year 
B) 10 M⨀per year 
C) 1 M⨀ per century 
D) 10 M⨀ per century 
E) 1 MV per million years 
A) 1 M⨀ per year 
B) 10 M⨀per year 
C) 1 M⨀ per century 
D) 10 M⨀ per century 
E) 1 MV per million years

Question 3

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 4

Describe two ways by which spiral structure may be induced in a spiral galaxy's disk.

Accepted Answer

Possibilities are:
(1)gravitational inte

Question 5

In most galaxies,the amount of dark matter and the amount of luminous matter is about equal.

Accepted Answer

A) True 
 B)False

Question 6

How have astronomers searched for evidence of MACHOs in the halo of the Milky Way?

Accepted Answer

A) They search for stars that are binary companions of MACHOs. 
B) They search for rapidly moving,massive gas clouds. 
C) They search for disturbances in the background of gravitational waves. 
D) They search for stars whose light is briefly amplified by gravitational lensing. 
E) They search for close binary stars undergoing mass transfer. 
A) They search for stars that are binary companions of MACHOs. 
B) They search for rapidly moving,massive gas clouds. 
C) They search for disturbances in the background of gravitational waves. 
D) They search for stars whose light is briefly amplified by gravitational lensing. 
E) They search for close binary stars undergoing mass transfer.

Question 7

The Hubble classification scheme for galaxies sorts them by:

Accepted Answer

A) their evolutionary state 
B) their mass 
C) the amount of dust 
D) the amount of dark matter 
E) their visual appearance 
A) their evolutionary state 
B) their mass 
C) the amount of dust 
D) the amount of dark matter 
E) their visual appearance

Question 8

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

Accepted Answer

A) True 
 B)False

Question 9

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 10

In some radio galaxies,we only see one side of the jet because:

Accepted Answer

A) the black hole only produces a jet in one direction 
B) of relativistic beaming 
C) the other side is inside the black hole's event horizon 
D) of dust obscuration 
E) of dark matter that blocks the light from one side of the jet 
A) the black hole only produces a jet in one direction 
B) of relativistic beaming 
C) the other side is inside the black hole's event horizon 
D) of dust obscuration 
E) of dark matter that blocks the light from one side of the jet

Question 11

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 12

Why is 21-cm radiation a good tracer of spiral arm structure?

Accepted Answer

A) Emitted by neutral hydrogen,it traces the location of high concentrations of gas. 
B) Emitted by O and B stars,it traces the location of newly formed stars. 
C) Emitted by ionized hydrogen,it traces the location of H II regions. 
D) Emitted by molecular hydrogen,it traces the location of clouds in the process of collapsing into stars. 
E) Emitted by red supergiants,it traces the presence of massive stars that are experiencing high rates of mass loss. 
A) Emitted by neutral hydrogen,it traces the location of high concentrations of gas. 
B) Emitted by O and B stars,it traces the location of newly formed stars. 
C) Emitted by ionized hydrogen,it traces the location of H II regions. 
D) Emitted by molecular hydrogen,it traces the location of clouds in the process of collapsing into stars. 
E) Emitted by red supergiants,it traces the presence of massive stars that are experiencing high rates of mass loss.

Question 13

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

Accepted Answer

There is currently n

Question 14

If the radio lobes of a radio galaxy extend out to 10 Mpc from the center of the galaxy and the particles in them are traveling at approximately 0.99 c,then how long must the black hole at the center have been ejecting this material into space? Note that 1 Mpc = 3.1 × 1022 m and 1 year = 3 × 107 s.

Accepted Answer

Because ν d/t,the length of ti

Question 15

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 16

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 17

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 18

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 19

What is the connection between active galaxies and galactic mergers?

Accepted Answer

Astronomers believe that galactic merger

Question 20

Galaxies that are classified as quasars were much more numerous in the past.

Accepted Answer

A) True 
 B)False

Exam 20: Galaxies

Seyfert galaxies are unique because they have large lobes of radio emission that extend well beyond the visible part of the galaxy.

Assume that when a supermassive black hole accretes gas,approximately 50 percent of its mass is converted directly into energy,which is radiated away.If a quasar has a luminosity of 1014 L⨀ then what must its mass accretion rate be?

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

Describe two ways by which spiral structure may be induced in a spiral galaxy's disk.

In most galaxies,the amount of dark matter and the amount of luminous matter is about equal.

How have astronomers searched for evidence of MACHOs in the halo of the Milky Way?

The Hubble classification scheme for galaxies sorts them by:

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

Elliptical galaxies appear red because:

In some radio galaxies,we only see one side of the jet because:

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

Why is 21-cm radiation a good tracer of spiral arm structure?

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

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?

Dust in galaxies does not count as dark matter because:

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

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

What is the connection between active galaxies and galactic mergers?

Galaxies that are classified as quasars were much more numerous in the past.

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 Adornments Moons 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

Assume that when a supermassive black hole accretes gas,approximately 50 percent of its mass is converted directly into energy,which is radiated away.If a quasar has a luminosity of 10¹⁴ L_⨀ then what must its mass accretion rate be?

If there is a 2 million M_⨀ black hole at the center of our galaxy,why is our own galaxy not an AGN?