Question 1

Based on the chemical abundances and velocities of stars in the Milky Way's disk and halo,we can conclude that the protogalactic fragments that came together to form the galaxy merged when the fragments had:

Accepted Answer

The chemical abundances and velocities of stars in the Milky Way's disk and halo suggest that the protogalactic fragments that formed the galaxy had already begun forming stars before they merged. This is consistent with current models of galaxy formation, which suggest that stars begin to form in individual protogalactic fragments before they merge to form a larger galaxy.

Question 2

By comparing globular clusters,you find that Cluster A's RR Lyrae stars are 225 times fainter than Cluster B's RR Lyrae stars.You know that both clusters have approximately the same chemical composition and age,and thus their RR Lyrae stars should have the same luminosities.Which cluster has the larger distance,and what is the ratio of the clusters' distances?

Accepted Answer

The answer of By comparing globular clusters,you find that Cluster...

Question 3

Magnetic fields in the Milky Way are concentrated in the disk because:

Accepted Answer

The magnetic fields in the Milky Way are tied to the charged particles in dense molecular clouds, which are concentrated in the disk. This is why the magnetic fields are predominantly found in the disk and not in the halo.

Question 4

Because of the ages of globular clusters in the Milky Way,we think our galaxy's early formation history was characterized by:

Accepted Answer

The answer of Because of the ages of globular clusters...

Question 5

What is the radius of the event horizon for the 4 × 10⁶ M_⨀ black hole at the center of the Milky Way?

Accepted Answer

The radius of the event horizon, or Schwarzschild radius, for a black hole is calculated using the formula $ R_s = \frac{2GM}{c^2} $. For a black hole with a mass of 4 × 10^6 solar masses, this radius is approximately 0.08 AU.

Question 6

If the central black hole started accreting a lot of gas,it would appear as what kind of an object?

Accepted Answer

If the central black hole started accreting a lot of gas, it would become an Active Galactic Nucleus (AGN). AGN is a highly luminous and compact region at the center of a galaxy that is powered by the accretion of gas onto a supermassive black hole.

Question 7

A typical globular cluster is composed of 500,000 stars in a sphere whose radius is approximately 5 pc.The distance between stars in a globular cluster is given approximately by d ≈ r/N¹^⁄³,where r is the radius and N is the number of stars in the cluster.Calculate this distance,and determine how many times smaller it is than the typical distance between stars in the solar neighborhood,which is 3 light-years.

Accepted Answer

The answer of A typical globular cluster is composed of...

Question 8

Explain how a standard candle allows you to determine the distance to an object.What is it that you have to measure or know about the standard candle to derive its distance?

Accepted Answer

The answer of Explain how a standard candle allows you...

Question 9

How have astronomers measured the mass of the black hole at the center of our galaxy?

Accepted Answer

Astronomers have measured the mass of the black hole at the center of our galaxy by observing the motions of stars near the center of the galaxy. These stars orbit an invisible object with a mass estimated to be 4.1 million times that of our Sun, indicating the presence of a supermassive black hole.

Question 10

Cosmic rays in the Milky Way are important because:

Accepted Answer

Cosmic rays in the Milky Way carry energy that is equivalent to that contained in magnetic fields and gas clouds. This energy is important for understanding the overall energy budget of the galaxy and the processes that shape its structure and evolution.

Question 11

Why do we know that at least one generation of stars formed and died before the Milky Way's globular clusters formed?

Accepted Answer

The answer of Why do we know that at least...

Question 12

Describe the differences between the ages and chemical abundances of globular and open star clusters.

Accepted Answer

The answer of Describe the differences between the ages and...

Question 13

How do we think the central black hole in the galaxy primarily grew to its current mass?

Accepted Answer

The most likely method for the growth of the central black hole in a galaxy is through the accretion of nearby gas. As gas falls towards the center of the galaxy, it can form a disk around the black hole, providing a source of fuel for it to grow. This process is thought to be responsible for the growth of supermassive black holes in the centers of galaxies, including our Milky Way. The other choices, while they may contribute to the overall growth of a black hole, are not thought to be the primary mechanism for its growth.

Question 14

Describe the population of globular star clusters in the Milky Way: how many are there,where do they reside in the Milky Way,and how do their ages and chemical abundances compare to the Sun?

Accepted Answer

The answer of Describe the population of globular star clusters...

Question 15

What are the main observational difficulties in observing the shape and spiral arm pattern of the Milky Way?

Accepted Answer

The answer of What are the main observational difficulties in...

Question 16

The oldest disk stars are both __________ and __________ compared to halo stars.

Accepted Answer

The answer of The oldest disk stars are both __________...

Question 17

What is ripping apart the Sagittarius dwarf spheroidal galaxy?

Accepted Answer

The gravitational tidal force of the Milky Way is pulling and stretching the Sagittarius dwarf spheroidal galaxy, causing it to be torn apart. This phenomenon is known as tidal stripping.

Question 18

Sagittarius A*,the radio source located at the center of our galaxy,is believed to be:

Accepted Answer

Sagittarius A* is believed to be a supermassive black hole based on its gravitational effects on stars orbiting around it and the observation of high-energy radiation near its location.

Question 19

The presence of dwarf galaxies around the Milky Way supports what picture of our galaxy's formation?

Accepted Answer

The presence of dwarf galaxies around the Milky Way supports the theory that our galaxy formed by the merger of smaller systems. This is because the dwarf galaxies are likely remnants of these smaller systems that were absorbed by the Milky Way during its formation.

Question 20

If the Large Magellanic Cloud is orbiting the Milky Way in a circular orbit with a speed of 175 km/s and a distance of 50 kpc from the center,how long would it take for the Large Magellanic Cloud to complete one orbit around the Milky Way?

Accepted Answer

The formula for orbital period is T = 2πr/v, where T is the period, r is the distance from the center of the orbit, and v is the velocity. Plugging in the given values, we get:
T = 2π(50 kpc)/(175 km/s) ≈ 1.14 billion years
Therefore, the best choice is B, 2 billion years, as it is the closest option to the calculated result.

Quiz 21: The Milky Waya Normal Spiral Galaxy

Based on the chemical abundances and velocities of stars in the Milky Way's disk and halo,we can conclude that the protogalactic fragments that came together to form the galaxy merged when the fragments had:

Magnetic fields in the Milky Way are concentrated in the disk because:

Because of the ages of globular clusters in the Milky Way,we think our galaxy's early formation history was characterized by:

What is the radius of the event horizon for the 4 × 10⁶ M_⨀ black hole at the center of the Milky Way?

If the central black hole started accreting a lot of gas,it would appear as what kind of an object?

Explain how a standard candle allows you to determine the distance to an object.What is it that you have to measure or know about the standard candle to derive its distance?

How have astronomers measured the mass of the black hole at the center of our galaxy?

Cosmic rays in the Milky Way are important because:

Why do we know that at least one generation of stars formed and died before the Milky Way's globular clusters formed?

Describe the differences between the ages and chemical abundances of globular and open star clusters.

How do we think the central black hole in the galaxy primarily grew to its current mass?

Describe the population of globular star clusters in the Milky Way: how many are there,where do they reside in the Milky Way,and how do their ages and chemical abundances compare to the Sun?

What are the main observational difficulties in observing the shape and spiral arm pattern of the Milky Way?

The oldest disk stars are both and compared to halo stars.

What is ripping apart the Sagittarius dwarf spheroidal galaxy?

Sagittarius A*,the radio source located at the center of our galaxy,is believed to be:

The presence of dwarf galaxies around the Milky Way supports what picture of our galaxy's formation?

If the Large Magellanic Cloud is orbiting the Milky Way in a circular orbit with a speed of 175 km/s and a distance of 50 kpc from the center,how long would it take for the Large Magellanic Cloud to complete one orbit around the Milky Way?

Quiz 21: The Milky Waya Normal Spiral Galaxy

Based on the chemical abundances and velocities of stars in the Milky Way's disk and halo,we can conclude that the protogalactic fragments that came together to form the galaxy merged when the fragments had:

Magnetic fields in the Milky Way are concentrated in the disk because:

Because of the ages of globular clusters in the Milky Way,we think our galaxy's early formation history was characterized by:

What is the radius of the event horizon for the 4 × 106 M⨀ black hole at the center of the Milky Way?

If the central black hole started accreting a lot of gas,it would appear as what kind of an object?

Explain how a standard candle allows you to determine the distance to an object.What is it that you have to measure or know about the standard candle to derive its distance?

How have astronomers measured the mass of the black hole at the center of our galaxy?

Cosmic rays in the Milky Way are important because:

Why do we know that at least one generation of stars formed and died before the Milky Way's globular clusters formed?

Describe the differences between the ages and chemical abundances of globular and open star clusters.

How do we think the central black hole in the galaxy primarily grew to its current mass?

Describe the population of globular star clusters in the Milky Way: how many are there,where do they reside in the Milky Way,and how do their ages and chemical abundances compare to the Sun?

What are the main observational difficulties in observing the shape and spiral arm pattern of the Milky Way?

The oldest disk stars are both __________ and __________ compared to halo stars.

What is ripping apart the Sagittarius dwarf spheroidal galaxy?

Sagittarius A*,the radio source located at the center of our galaxy,is believed to be:

The presence of dwarf galaxies around the Milky Way supports what picture of our galaxy's formation?

If the Large Magellanic Cloud is orbiting the Milky Way in a circular orbit with a speed of 175 km/s and a distance of 50 kpc from the center,how long would it take for the Large Magellanic Cloud to complete one orbit around the Milky Way?

What is the radius of the event horizon for the 4 × 10⁶ M_⨀ black hole at the center of the Milky Way?

The oldest disk stars are both and compared to halo stars.