Question 1

An astronomer discovers an unusual active galactic nucleus without any orbiting clouds.How would such a source differ from a typical quasar?
A) It would lack emission lines.
B) It would lack a jet.
C) It would not have variability.
D) all of the above

Accepted Answer

Active galactic nuclei (AGNs) typically have orbiting clouds of gas and dust that emit light at specific wavelengths, creating emission lines in their spectra. Without these clouds, an AGN would lack these characteristic emission lines, differentiating it from a typical quasar, which is a type of AGN known for its strong emission lines. The presence of a jet or variability does not depend on the orbiting clouds.

Question 2

A bright source doubles its luminosity over the course of a week.How large is the source?
A) 12 AU
B) 1200 AU
C) 0.12 parsecs
D) 1.2 parsecs

Accepted Answer

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Question 3

Which astronomer discovered dark matter in spiral galaxies?
A) Harlow Shapley
B) Edwin Hubble
C) Arno Penzias
D) Vera Rubin

Accepted Answer

Vera Rubin discovered dark matter in spiral galaxies through her observations of the rotations of stars within them.

Question 4

What type of galaxy is shown in the image below?

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Question 5

Why was the large size of Edwin Hubble's telescope essential for resolving the nature of spiral nebulae?

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Question 6

Which cosmic distance measurement techniques rely on the observation of standard candles?

Accepted Answer

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Question 7

What are the four major classes of galaxies in the Universe?

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Question 8

The figure below shows the rotation curves of several spiral galaxies,extending to the very edge of their visible disks.What do these curves tell us about the distribution of dark matter in these galaxies? 
A) Most of the dark matter is in clumps.
B) Most of the dark matter is in the bulge.
C) Most of the dark matter is near stars.
D) Most of the dark matter is in the galaxies' outskirts.

Accepted Answer

The rotation curves show that the outer parts of the spiral galaxies are rotating faster than expected based on the visible matter alone. This implies the presence of additional matter, which we call "dark matter", and that it is distributed throughout the outer regions of the galaxies. Therefore, the most plausible explanation is that most of the dark matter is in the galaxies' outskirts.

Question 9

A black hole with a mass of 10⁹ MSᵤn brightens rapidly and increases its luminosity by a factor of two.Approximately how long would it take for an observer on Earth to see the black hole reach its maximum brightness?
A) 3 minutes
B) 3 hours
C) 3 days
D) 3 weeks

Accepted Answer

The time it takes for a black hole to brighten and reach its maximum brightness depends on the accretion rate and the physics of the accretion disk around the black hole, not on the speed of light or the distance from Earth. The given options suggest a range of timescales that are typical for various astrophysical processes. A timescale of hours is reasonable for changes in the accretion disk of a supermassive black hole, which can lead to rapid increases in luminosity observable from Earth.

Question 10

The mass of a supermassive black hole within the galaxy will most accurately predict the:
A) total mass of the galaxy.
B) mass of the galaxy's stellar halo.
C) mass of the galaxy's bulge.
D) mass of the galaxy's gas clouds.

Accepted Answer

The mass of a supermassive black hole within a galaxy is directly correlated with the mass of the galaxy's bulge. Therefore, knowing the mass of the supermassive black hole can give an accurate prediction of the mass of the galaxy's bulge.

Question 11

Name three aspects of elliptical galaxies that point toward their origin in collisions between galaxies.

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Question 12

Why were Cepheid variables essential to the discovery of galaxies outside the Milky Way?

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Question 13

Which of the following quantities is most useful to astronomers when measuring the dark matter content of galaxies?
A) color
B) age
C) stellar velocities
D) luminosity

Accepted Answer

Stellar velocities are most useful for measuring the dark matter content of galaxies. This is because the gravitational pull of dark matter affects the motion of stars in a galaxy, causing them to move at higher velocities than expected based on the visible mass alone. By studying the velocities of stars in a galaxy, astronomers can determine the amount of dark matter present. Color, age, and luminosity are all properties of stars that can provide useful information for astronomers, but they are not directly related to measuring the dark matter content of galaxies.

Question 14

Two elliptical galaxies have identical radii and luminosities,but stars in galaxy A have a maximum orbital speed three times that of galaxy B.How much more massive is galaxy A than galaxy B?
A) nine times more
B) three times more
C) 1.7 times more
D) 1.3 times more

Accepted Answer

The mass of a galaxy can be estimated using the formula derived from the virial theorem, which relates the mass of a galaxy to the orbital speed of its stars (v) and the radius (r) of the galaxy. Since the radii are identical and only the orbital speeds differ, the mass is directly proportional to the square of the orbital speed (v^2). If the maximum orbital speed in galaxy A is three times that of galaxy B, then the mass of galaxy A is 3^2 = 9 times more massive than galaxy B.

Question 15

Why is it important for astronomers to find galaxies with Type Ia supernova and Cepheid variables?

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Question 16

The figure below shows a schematic diagram of an active galactic nucleus.Which region is responsible for broad emission lines? 
A) A
B) B
C) C
D) D

Accepted Answer

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Question 17

How do astronomers most directly measure the amount of dark matter in elliptical galaxies?
A) through their rotation curves
B) through their velocity dispersion
C) through their radii
D) through their reddening

Accepted Answer

Astronomers most directly measure the amount of dark matter in elliptical galaxies through their velocity dispersion, which is the measure of the range of velocities of stars within the galaxy. The velocity dispersion is affected by both the visible and dark matter components of the galaxy. By comparing the observed velocity dispersion with theoretical predictions, astronomers can estimate the amount of dark matter in the galaxy.

Question 18

Why are the bars in barred spiral galaxies typically bright?

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Question 19

The figure below shows three spiral galaxies.Classify them as Sa,Sb,and Sc galaxies.There is one of each type of galaxy in the figure.

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Question 20

Contrast spiral and elliptical galaxies in terms of their color,gas content,and orbital properties.

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Quiz 16: A Universe of Galaxies

An astronomer discovers an unusual active galactic nucleus without any orbiting clouds.How would such a source differ from a typical quasar?

A bright source doubles its luminosity over the course of a week.How large is the source?

Which astronomer discovered dark matter in spiral galaxies?

What type of galaxy is shown in the image below?

Why was the large size of Edwin Hubble's telescope essential for resolving the nature of spiral nebulae?

Which cosmic distance measurement techniques rely on the observation of standard candles?

What are the four major classes of galaxies in the Universe?

The figure below shows the rotation curves of several spiral galaxies,extending to the very edge of their visible disks.What do these curves tell us about the distribution of dark matter in these galaxies?

A black hole with a mass of 10⁹ MSᵤn brightens rapidly and increases its luminosity by a factor of two.Approximately how long would it take for an observer on Earth to see the black hole reach its maximum brightness?

The mass of a supermassive black hole within the galaxy will most accurately predict the:

Name three aspects of elliptical galaxies that point toward their origin in collisions between galaxies.

Why were Cepheid variables essential to the discovery of galaxies outside the Milky Way?

Which of the following quantities is most useful to astronomers when measuring the dark matter content of galaxies?

Two elliptical galaxies have identical radii and luminosities,but stars in galaxy A have a maximum orbital speed three times that of galaxy B.How much more massive is galaxy A than galaxy B?

Why is it important for astronomers to find galaxies with Type Ia supernova and Cepheid variables?

The figure below shows a schematic diagram of an active galactic nucleus.Which region is responsible for broad emission lines?

How do astronomers most directly measure the amount of dark matter in elliptical galaxies?

Why are the bars in barred spiral galaxies typically bright?

The figure below shows three spiral galaxies.Classify them as Sa,Sb,and Sc galaxies.There is one of each type of galaxy in the figure.

Contrast spiral and elliptical galaxies in terms of their color,gas content,and orbital properties.