Question 1

Neutral hydrogen atoms are found only inside dense clouds where they are shielded from stellar radiation.

Accepted Answer

Neutral hydrogen atoms can be ionized by the strong ultraviolet radiation from hot stars. Therefore, they are generally found only in dense clouds where they are shielded from such radiation.

Question 2

There is a 10⁹ M_$\odot$ black hole at the center of the Milky Way that is rapidly accreting stars and gas.

Accepted Answer

The black hole at the center of the Milky Way, Sagittarius A*, has a mass of about 4 million solar masses (4 x 10^6 M☉) and is not rapidly accreting stars and gas.

Question 3

Cosmic rays come mostly from extragalactic sources and contribute little to the overall energy balance in the Milky Way disk.

Accepted Answer

False

Question 4

Our galaxy is a typical barred spiral galaxy.

Accepted Answer

Our Milky Way galaxy is indeed a barred spiral galaxy. It has a bar-shaped structure at its center, with spiral arms extending outward from the ends of the bar.

Question 5

Stars in the Milky Way that are 12 to 13 billion years old are only found in globular clusters.

Accepted Answer

The answer of Stars in the Milky Way that are...

Question 6

The coldest molecular clouds in our galaxy have temperatures of approximately 1000 K.

Accepted Answer

The coldest molecular clouds in our galaxy have temperatures of approximately 10 K, not 1000 K.

Question 7

Every open star cluster in the Milky Way is younger than even the youngest globular cluster.

Accepted Answer

Open star clusters are formed from the same molecular cloud, hence they are relatively young (few million years old) while globular clusters are formed during the early stage of galaxy formation hence they are relatively old (few billion years old).

Question 8

The chemical abundance of a main-sequence star usually reflects how much nuclear burning has gone on inside it.

Accepted Answer

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Question 9

The Milky Way has two major spiral arms that emanate from the ends of its bar.

Accepted Answer

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Question 10

There are many more individual stars residing in the Milky Way stellar halo than inside globular clusters.

Accepted Answer

The Milky Way's stellar halo is estimated to contain up to a trillion stars, while the total number of stars in all known globular clusters within the Milky Way is estimated to be in the range of a few hundred million to a few billion. Therefore, there are many more individual stars in the Milky Way stellar halo than inside globular clusters.

Question 11

Stars forming in molecular clouds tend to form first in the low-density periphery.

Accepted Answer

The answer of Stars forming in molecular clouds tend to...

Question 12

Open clusters are only found in the disk of the Milky Way; globular clusters are only found in the halo of the Milky Way.

Accepted Answer

While it is true that open clusters are primarily found in the disk of the Milky Way, some are also found in the halo. Similarly, while globular clusters are primarily found in the halo, a few have been found within the disk.

Question 13

The dust in the interstellar medium comes primarily from stellar winds of main-sequence stars.

Accepted Answer

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Question 14

The only effect of interstellar dust is that it makes objects appear redder than they really are.

Accepted Answer

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Question 15

We observe molecular hydrogen gas (H₂)using 21-cm emission.

Accepted Answer

21-cm emission is a characteristic of atomic hydrogen (H I), not molecular hydrogen (H₂).

Question 16

Our galaxy is classified as an Sd galaxy in the Hubble sequence.

Accepted Answer

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Question 17

The average density of the interstellar medium is many times less dense than the best vacuum on Earth.

Accepted Answer

The interstellar medium is considered a low-density environment, with an average density of about 1 atom per cubic centimeter. This is much less dense than the best vacuum on Earth, which can have a density of about 10^-8 atoms per cubic centimeter.

Question 18

Halo stars formed before gas in the Milky Way collapsed to form the disk.

Accepted Answer

Halo stars are thought to have formed in the early universe and were pulled into the Milky Way's gravitational field as it was forming. The gas that collapsed to form the disk of the Milky Way came later.

Question 19

Globular clusters have much higher stellar densities than the local solar neighborhood.

Accepted Answer

Globular clusters are densely packed groups of stars, with densities ranging from hundreds to thousands of stars per cubic parsec. In comparison, the star density in the local solar neighborhood is about one star per cubic parsec.

Question 20

The lowest-density gas in the interstellar medium is also the coldest.

Accepted Answer

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Quiz 16: Our Galaxy: The Milky Way