Question 1

The images in the figure below are both of the Milky Way.Why can more detail be seen in the infrared image than in the visible light image?

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The answer of The images in the figure below are...

Question 2

When winds blow the gas away from a forming protostar, the protostar

Accepted Answer

When winds blow the gas away from a forming protostar, it becomes visible as a T Tauri star, which is a young, pre-main-sequence star.

Question 3

Which of the following stars spend the longest time on their Hayashi tracks?

Accepted Answer

0.08 M_SUN stars, which are at the lower end of the main sequence, spend the longest time on their Hayashi tracks because they have lower masses and thus evolve more slowly compared to more massive stars.

Question 4

In the densest molecular clouds, the average density is approximately 300 atoms/cm³.If a cube of molecular cloud gas with this density contained 100 M_SUN of material (the amount needed to make a 1 M_SUN star), what would be the length of a side of the cube in units of AU? For reference, the mass of the Sun is 2 *10³⁰ kg, the mass of a hydrogen atom is 1.7 *10 ^- ²⁷ kg, and 1 AU = 1.5 *10¹¹ m.

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The answer of In the densest molecular clouds, the average...

Question 5

When a molecular cloud fragments,

Accepted Answer

The most massive stars form first because they can accumulate mass more quickly due to their stronger gravitational pull.

Question 6

What is the interstellar medium made of? Give rough percentages of each.

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The answer of What is the interstellar medium made of?...

Question 7

Suppose we observe two molecular clouds containing dust.The dust in Cloud 1 peaks in emission at 50 mm, while the dust in Cloud 2 peaks in emission at 78 mm.How much warmer is the dust in Cloud 1 compared to Cloud 2?

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The answer of Suppose we observe two molecular clouds containing...

Question 8

Herbig-Haro objects are almost always found

Accepted Answer

Herbig-Haro objects are typically found in pairs on either side of a young protostar, as they are formed by jets of gas ejected by the protostar colliding with the surrounding interstellar medium.

Question 9

How are typical interstellar gas clouds different from the clouds that we see in Earth's sky?

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The answer of How are typical interstellar gas clouds different...

Question 10

Compare the volume of the Sun with the volume of interstellar space it dominates.Is the occupied percentage large or small? Consider the volume around the Sun to be a sphere whose radius is equal to the distance to the nearest star, which is equal to 5 light-years.(Note: the radius of the Sun is 7 *10⁵ km, and 1 light-year = 9.5 * 10¹² km.)

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The answer of Compare the volume of the Sun with...

Question 11

Where have astronomers observed the existence of planets?

Accepted Answer

Astronomers have observed planets in our Solar System, orbiting other stars (exoplanets), in binary systems, and rogue planets traveling through the Milky Way without orbiting a star.

Question 12

How are H II regions and the hot intercloud gas heated?

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The answer of How are H II regions and the...

Question 13

Suppose the 21-cm photon of neutral hydrogen were instead emitted at 500 nm (i.e., a visible blue photon).Would it still be a useful probe of the Milky Way's structure? Why?

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The answer of Suppose the 21-cm photon of neutral hydrogen...

Question 14

Which of the following stars spend the LEAST amount of time on their Hayashi tracks?

Accepted Answer

Type B main-sequence stars are massive and have high luminosities, causing them to evolve quickly and spend the least amount of time on their Hayashi tracks compared to less massive stars.

Question 15

If you could watch stars forming out of a gas cloud, which stars would form first?

Accepted Answer

High-mass stars form first because they have stronger gravitational forces that allow them to accumulate mass more quickly from the surrounding gas cloud.

Question 16

Star formation is an inefficient process, with only a few percent of the initial cloud fragment ending up as stars.This means the initial mass of a molecular cloud fragment that formed a 2 M_SUN star was probably close to

Accepted Answer

Star formation is inefficient, with only a few percent of the cloud's mass forming stars. To form a 2 M_SUN star, the initial cloud mass would need to be significantly larger, around 100 M_SUN, to account for the inefficiency.

Question 17

Bipolar outflows create bright bow shocks because

Accepted Answer

Bipolar outflows create bright bow shocks primarily because the material in the outflows collides with particles in the interstellar medium, causing compression and heating, which results in the emission of light.

Question 18

Why do molecules readily exist in Earth's atmosphere but not in most of interstellar space?

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The answer of Why do molecules readily exist in Earth's...

Question 19

What is the difference between interstellar extinction and interstellar reddening?

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The answer of What is the difference between interstellar extinction...

Question 20

How long does it typically take for a protostar to form a 1 M_SUN star?

Accepted Answer

A protostar is a young star that is still forming. It takes about 10 million years for a protostar to form a 1 M_SUN star.

Quiz 15: The Interstellar Medium and Star Formation