Question 1

Why is the black hole at the center of the Milky Way growing very slowly in comparison to some other black holes?

Accepted Answer

A)  It is much smaller than the black holes in other galaxies. 
B)  The surrounding gas is too hot. 
C)  There is no nearby matter that could fall into the black hole. 
D)  The nearby matter is composed only of positrons, which annihilate with electrons before they can fall onto the black hole. 
A)  It is much smaller than the black holes in other galaxies. 
B)  The surrounding gas is too hot. 
C)  There is no nearby matter that could fall into the black hole. 
D)  The nearby matter is composed only of positrons, which annihilate with electrons before they can fall onto the black hole.

Question 2

The idea that some of the nebulae that are observed in the sky might be "island universes," immense collections of stars far beyond the Milky Way, was first proposed by

Accepted Answer

A)  Immanuel Kant in 1755. 
B)  Albert Einstein in 1909. 
C)  Heber Curtis in 1920. 
D)  Lord Rosse in 1845. 
A)  Immanuel Kant in 1755. 
B)  Albert Einstein in 1909. 
C)  Heber Curtis in 1920. 
D)  Lord Rosse in 1845.

Question 3

Recent observations seem to indicate that, rather than being a spiral galaxy, the Milky Way may be

Accepted Answer

A)  a barred spiral with a definite, straight bar across its center. 
B)  an irregular galaxy in which matter is distributed chaotically. 
C)  an elliptical galaxy with little structure. 
D)  two elliptical galaxies colliding with one another, in view of the very active star formation within the galactic plane, brought about by the vastly increased density during the collision. 
A)  a barred spiral with a definite, straight bar across its center. 
B)  an irregular galaxy in which matter is distributed chaotically. 
C)  an elliptical galaxy with little structure. 
D)  two elliptical galaxies colliding with one another, in view of the very active star formation within the galactic plane, brought about by the vastly increased density during the collision.

Question 4

The major features of the Milky Way Galaxy have been found to include all of these EXCEPT

Accepted Answer

A)  more than 100 billion stars. 
B)  a bar of stars running through the center. 
C)  a spherical symmetry. 
D)  spiral arms. 
A)  more than 100 billion stars. 
B)  a bar of stars running through the center. 
C)  a spherical symmetry. 
D)  spiral arms.

Question 5

Why are astronomers on Earth able to see only a relatively small part of the Milky Way Galaxy?

Accepted Answer

A)  There are so many stars in the Milky Way that the more distant ones are hidden behind the nearer ones. 
B)  Distant stars are obscured by gas in interstellar space. 
C)  Expansion of the universe has carried the more distant stars out of view. 
D)  Distant stars are obscured by dust in interstellar space. 
A)  There are so many stars in the Milky Way that the more distant ones are hidden behind the nearer ones. 
B)  Distant stars are obscured by gas in interstellar space. 
C)  Expansion of the universe has carried the more distant stars out of view. 
D)  Distant stars are obscured by dust in interstellar space.

Question 6

The Andromeda Galaxy (M31) is BEST described as a(n)

Accepted Answer

A)  extension of the Milky Way. 
B)  vortex surrounding a black hole. 
C)  gaseous nebula extending for 6° across the sky. 
D)  spiral collection of stars, dust, and gas 2 million ly away. 
A)  extension of the Milky Way. 
B)  vortex surrounding a black hole. 
C)  gaseous nebula extending for 6° across the sky. 
D)  spiral collection of stars, dust, and gas 2 million ly away.

Question 7

If the black hole in the center of the Galaxy is 4 * 106 solar masses, what would be its radius (that is, the radius of its event horizon)?

Accepted Answer

A)  1.2 * 107 m (about twice the radius of Earth) 
B)  1.2 * 109 m (about twice the radius of the Sun) 
C)  1.2 * 1010 m (about one-fifth of Mercury's orbital radius) 
D)  1.2 * 1012 m (almost twice Jupiter's orbital radius) 
A)  1.2 * 107 m (about twice the radius of Earth) 
B)  1.2 * 109 m (about twice the radius of the Sun) 
C)  1.2 * 1010 m (about one-fifth of Mercury's orbital radius) 
D)  1.2 * 1012 m (almost twice Jupiter's orbital radius)

Question 8

Suppose astronomers could examine a star and determine its apparent magnitude M without any intervening gas and dust. Compared to its apparent magnitude measured with gas and dust between Earth and the star, this "clean" measurement of M would be

Accepted Answer

A)  a larger number. 
B)  a smaller number. 
C)  the same number. 
D)  either larger or smaller depending on the star's speed (toward or away). 
A)  a larger number. 
B)  a smaller number. 
C)  the same number. 
D)  either larger or smaller depending on the star's speed (toward or away).

Question 9

What evidence now exists for a supermassive black hole at the center of the Milky Way Galaxy?

Accepted Answer

A)  very bright, steady X-ray emissions from the galactic center 
B)  observations of intense inflow of matter toward the center of the Galaxy as seen by light, Doppler-shifted toward the red, emitted by this matter 
C)  very rapid motion of matter close to the nucleus of the Galaxy, requiring a very massive body to hold it in orbit 
D)  very dark void in an otherwise bright region of space near the galactic center, indicating the presence of a black hole 
A)  very bright, steady X-ray emissions from the galactic center 
B)  observations of intense inflow of matter toward the center of the Galaxy as seen by light, Doppler-shifted toward the red, emitted by this matter 
C)  very rapid motion of matter close to the nucleus of the Galaxy, requiring a very massive body to hold it in orbit 
D)  very dark void in an otherwise bright region of space near the galactic center, indicating the presence of a black hole

Question 10

The period-luminosity relationship for Cepheid variable stars, relating variability to absolute overall brightness, was discovered by

Accepted Answer

A)  Harlow Shapley. 
B)  Henrietta Leavitt. 
C)  Edwin Hubble. 
D)  Sir Isaac Newton. 
A)  Harlow Shapley. 
B)  Henrietta Leavitt. 
C)  Edwin Hubble. 
D)  Sir Isaac Newton.

Question 11

In 1917, Harlow Shapley plotted the positions of almost a hundred globular clusters. But the galactic plane is cloaked by gas and dust, and the best way to "see" through this is with long wavelength radio waves. However, in 1917 radio astronomy did not exist. How did Shapley accomplish his task?

Accepted Answer

A)  He could only see globulars that were relatively close to the Sun. 
B)  He concentrated on using the long-wavelength end of the visible spectrum-red. This worked well because globulars are old and are dominated by red stars. 
C)  The globulars are mostly in a halo up off the galactic plane, so the dust was not a great problem. 
D)  In order to form a globular cluster, a great deal of interstellar dust is used up. Thus, globulars create holes in the dust and are relatively easy to see. 
A)  He could only see globulars that were relatively close to the Sun. 
B)  He concentrated on using the long-wavelength end of the visible spectrum-red. This worked well because globulars are old and are dominated by red stars. 
C)  The globulars are mostly in a halo up off the galactic plane, so the dust was not a great problem. 
D)  In order to form a globular cluster, a great deal of interstellar dust is used up. Thus, globulars create holes in the dust and are relatively easy to see.

Question 12

A classical Cepheid variable star is seen to vary regularly with a period of 25 days. Approximately how many times brighter than the Sun would this star appear to be if it were to replace the Sun in the solar system? Refer to Figure 16-4 from the text.

Accepted Answer

A)  1000 
B)  4 
C)  10,000 
D)  102 
A)  1000 
B)  4 
C)  10,000 
D)  102

Question 13

Radio waves of 21-cm wavelength originate from which component of the interstellar medium?

Accepted Answer

A)  cool, neutral atomic hydrogen 
B)  cold molecular hydrogen, H2 
C)  cool carbon monoxide, CO 
D)  hot, ionized atomic hydrogen 
A)  cool, neutral atomic hydrogen 
B)  cold molecular hydrogen, H2 
C)  cool carbon monoxide, CO 
D)  hot, ionized atomic hydrogen

Question 14

What was the implication of the observation by Hubble that the Cepheid variable stars he measured in the Andromeda "nebula" appeared to be very faint compared with what was expected?

Accepted Answer

A)  The observed period was affected by the intense gravitational field of the "nebula" as predicted by general relativity, leading to incorrect luminosity determination. 
B)  The Andromeda "nebula" was very far away and was in fact a galaxy. 
C)  Hubble had discovered a new class of intrinsically faint Cepheid variable stars. 
D)  Dust and gas in the "nebula" had severely reduced the light from these stars. 
A)  The observed period was affected by the intense gravitational field of the "nebula" as predicted by general relativity, leading to incorrect luminosity determination. 
B)  The Andromeda "nebula" was very far away and was in fact a galaxy. 
C)  Hubble had discovered a new class of intrinsically faint Cepheid variable stars. 
D)  Dust and gas in the "nebula" had severely reduced the light from these stars.

Question 15

The orbits of stars around the center of the Milky Way Galaxy suggest that the mass at the center of the Galaxy is about 4 million solar masses. What is believed to be the diameter of this supermassive object?

Accepted Answer

A)  about half a parsec 
B)  about 8 ly 
C)  smaller than Earth's orbit 
D)  smaller than the diameter of the Sun 
A)  about half a parsec 
B)  about 8 ly 
C)  smaller than Earth's orbit 
D)  smaller than the diameter of the Sun

Question 16

The ratio of thickness to diameter of the Milky Way Galaxy is

Accepted Answer

A)  1/500. 
B)  1/5. 
C)  1/50. 
D)  1/1000. 
A)  1/500. 
B)  1/5. 
C)  1/50. 
D)  1/1000.

Question 17

What physical process has allowed astronomers to rule out brown dwarfs as the source of dark matter in the Milky Way Galaxy?

Accepted Answer

A)  The gravitational fields of brown dwarfs can bend the light from background stars. 
B)  Brown dwarfs emit copious amounts of infrared radiation, which can penetrate the interstellar medium. 
C)  Molecules in the atmospheres of brown dwarfs emit radio waves that can be detected from Earth. 
D)  Brown dwarfs occasionally eclipse (block the light from) more distant stars. 
A)  The gravitational fields of brown dwarfs can bend the light from background stars. 
B)  Brown dwarfs emit copious amounts of infrared radiation, which can penetrate the interstellar medium. 
C)  Molecules in the atmospheres of brown dwarfs emit radio waves that can be detected from Earth. 
D)  Brown dwarfs occasionally eclipse (block the light from) more distant stars.

Question 18

Harlow Shapley's original estimate of the distance from the Sun to the galactic center was incorrect because it did not take scattering by interstellar dust into account. Shapley's original estimate was

Accepted Answer

A)  too large because light scattering and absorption by dust made nearer stars look dim-as though they were more distant. 
B)  too large because scattering by dust made stars look redder-as though they were highly Doppler-shifted and thus more distant. 
C)  too small because gas and dust tend to reflect light into the path of the beam, thus making stars look brighter and nearer. 
D)  too large because scattering by dust made stars look redder-as though they were red giants of larger luminosity and thus farther away. 
A)  too large because light scattering and absorption by dust made nearer stars look dim-as though they were more distant. 
B)  too large because scattering by dust made stars look redder-as though they were highly Doppler-shifted and thus more distant. 
C)  too small because gas and dust tend to reflect light into the path of the beam, thus making stars look brighter and nearer. 
D)  too large because scattering by dust made stars look redder-as though they were red giants of larger luminosity and thus farther away.

Question 19

The 21-cm line is one of the most important wavelengths in radio astronomy. The fact that it is a relatively long wavelength is important because long wavelengths

Accepted Answer

A)  are more likely to interact with clouds of gas and dust. 
B)  are more likely to pass through clouds of gas and dust. 
C)  carry more energy than short wavelengths of the same energy. 
D)  can be detected with greater resolution than can short wavelengths. 
A)  are more likely to interact with clouds of gas and dust. 
B)  are more likely to pass through clouds of gas and dust. 
C)  carry more energy than short wavelengths of the same energy. 
D)  can be detected with greater resolution than can short wavelengths.

Question 20

In a recent survey of stars in the sky, it was found that occasionally a star that is normally of constant brightness will slowly brighten and then fade back to its original brightness again over the space of several weeks. What is believed to be the cause of this change in brightness?

Accepted Answer

A)  massive coronal ejection on a star with abnormally strong magnetic fields 
B)  gradual motion of the star through a break or hole between interstellar dust clouds 
C)  microlensing by compact objects such as brown dwarfs passing in front of the star 
D)  "lighthouse beam" of a slowly rotating neutron star companion 
A)  massive coronal ejection on a star with abnormally strong magnetic fields 
B)  gradual motion of the star through a break or hole between interstellar dust clouds 
C)  microlensing by compact objects such as brown dwarfs passing in front of the star 
D)  "lighthouse beam" of a slowly rotating neutron star companion

Why is the black hole at the center of the Milky Way growing very slowly in comparison to some other black holes?

The idea that some of the nebulae that are observed in the sky might be "island universes," immense collections of stars far beyond the Milky Way, was first proposed by

Recent observations seem to indicate that, rather than being a spiral galaxy, the Milky Way may be

The major features of the Milky Way Galaxy have been found to include all of these EXCEPT

Why are astronomers on Earth able to see only a relatively small part of the Milky Way Galaxy?

The Andromeda Galaxy (M31) is BEST described as a(n)

If the black hole in the center of the Galaxy is 4 * 10⁶ solar masses, what would be its radius (that is, the radius of its event horizon)?

Suppose astronomers could examine a star and determine its apparent magnitude M without any intervening gas and dust. Compared to its apparent magnitude measured with gas and dust between Earth and the star, this "clean" measurement of M would be

What evidence now exists for a supermassive black hole at the center of the Milky Way Galaxy?

The period-luminosity relationship for Cepheid variable stars, relating variability to absolute overall brightness, was discovered by

In 1917, Harlow Shapley plotted the positions of almost a hundred globular clusters. But the galactic plane is cloaked by gas and dust, and the best way to "see" through this is with long wavelength radio waves. However, in 1917 radio astronomy did not exist. How did Shapley accomplish his task?

A classical Cepheid variable star is seen to vary regularly with a period of 25 days. Approximately how many times brighter than the Sun would this star appear to be if it were to replace the Sun in the solar system? Refer to Figure 16-4 from the text.

Radio waves of 21-cm wavelength originate from which component of the interstellar medium?

What was the implication of the observation by Hubble that the Cepheid variable stars he measured in the Andromeda "nebula" appeared to be very faint compared with what was expected?

The orbits of stars around the center of the Milky Way Galaxy suggest that the mass at the center of the Galaxy is about 4 million solar masses. What is believed to be the diameter of this supermassive object?

The ratio of thickness to diameter of the Milky Way Galaxy is

What physical process has allowed astronomers to rule out brown dwarfs as the source of dark matter in the Milky Way Galaxy?

Harlow Shapley's original estimate of the distance from the Sun to the galactic center was incorrect because it did not take scattering by interstellar dust into account. Shapley's original estimate was

The 21-cm line is one of the most important wavelengths in radio astronomy. The fact that it is a relatively long wavelength is important because long wavelengths

In a recent survey of stars in the sky, it was found that occasionally a star that is normally of constant brightness will slowly brighten and then fade back to its original brightness again over the space of several weeks. What is believed to be the cause of this change in brightness?

Discovering the Night Sky

Gravitation and the Motion of the Planets

Light and Telescopes

Atomic Physics and Spectra

Exoplanets and the Formation of Planetary Systems

Formation of the Solar System

Earth and the Moon

The Other Terrestrial Planets

The Outer Planets

Vagabonds of the Solar System

The Sun: Our Extraordinary Star

Characterizing Stars

The Lives of Stars From Birth Through Middle Age

The Death of Stars

Black Holes: Matters of Gravity

Galaxies

Quasars and Other Active Galaxies

Cosmology

Astrobiology

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Exam 16: The Milky Way Galaxy

Why is the black hole at the center of the Milky Way growing very slowly in comparison to some other black holes?

The idea that some of the nebulae that are observed in the sky might be "island universes," immense collections of stars far beyond the Milky Way, was first proposed by

Recent observations seem to indicate that, rather than being a spiral galaxy, the Milky Way may be

The major features of the Milky Way Galaxy have been found to include all of these EXCEPT

Why are astronomers on Earth able to see only a relatively small part of the Milky Way Galaxy?

The Andromeda Galaxy (M31) is BEST described as a(n)

If the black hole in the center of the Galaxy is 4 * 106 solar masses, what would be its radius (that is, the radius of its event horizon)?

Suppose astronomers could examine a star and determine its apparent magnitude M without any intervening gas and dust. Compared to its apparent magnitude measured with gas and dust between Earth and the star, this "clean" measurement of M would be

What evidence now exists for a supermassive black hole at the center of the Milky Way Galaxy?

The period-luminosity relationship for Cepheid variable stars, relating variability to absolute overall brightness, was discovered by

In 1917, Harlow Shapley plotted the positions of almost a hundred globular clusters. But the galactic plane is cloaked by gas and dust, and the best way to "see" through this is with long wavelength radio waves. However, in 1917 radio astronomy did not exist. How did Shapley accomplish his task?

A classical Cepheid variable star is seen to vary regularly with a period of 25 days. Approximately how many times brighter than the Sun would this star appear to be if it were to replace the Sun in the solar system? Refer to Figure 16-4 from the text.

Radio waves of 21-cm wavelength originate from which component of the interstellar medium?

What was the implication of the observation by Hubble that the Cepheid variable stars he measured in the Andromeda "nebula" appeared to be very faint compared with what was expected?

The orbits of stars around the center of the Milky Way Galaxy suggest that the mass at the center of the Galaxy is about 4 million solar masses. What is believed to be the diameter of this supermassive object?

The ratio of thickness to diameter of the Milky Way Galaxy is

What physical process has allowed astronomers to rule out brown dwarfs as the source of dark matter in the Milky Way Galaxy?

Harlow Shapley's original estimate of the distance from the Sun to the galactic center was incorrect because it did not take scattering by interstellar dust into account. Shapley's original estimate was

The 21-cm line is one of the most important wavelengths in radio astronomy. The fact that it is a relatively long wavelength is important because long wavelengths

In a recent survey of stars in the sky, it was found that occasionally a star that is normally of constant brightness will slowly brighten and then fade back to its original brightness again over the space of several weeks. What is believed to be the cause of this change in brightness?

Discovering the Night Sky

Gravitation and the Motion of the Planets

Light and Telescopes

Atomic Physics and Spectra

Exoplanets and the Formation of Planetary Systems

Formation of the Solar System

Earth and the Moon

The Other Terrestrial Planets

The Outer Planets

Vagabonds of the Solar System

The Sun: Our Extraordinary Star

Characterizing Stars

The Lives of Stars From Birth Through Middle Age

The Death of Stars

Black Holes: Matters of Gravity

Galaxies

Quasars and Other Active Galaxies

Cosmology

Astrobiology

Filters

If the black hole in the center of the Galaxy is 4 * 10⁶ solar masses, what would be its radius (that is, the radius of its event horizon)?