Question 1

Why is carbon important to the energy-generation process in a massive star?

Accepted Answer

It acts as a catalyst in the CNO fusion cycle.

Question 2

What is a proplyd?

Accepted Answer

A)   the smallest form of molecular cloud
B)   a bright knot in a protostellar jet
C)   the visible result of colliding winds
D)   none of the above C

Question 3

How do the density and central temperature change as it approaches the main sequence?

Accepted Answer

The density and central temperature increase.

Question 4

Which of the following effects would extend the lifetime of a protostar (before it becomes a star),if everything else remained the same?

Accepted Answer

A)   increase the opacity of the protostar material
B)   increase the luminosity of the protostar
C)   increase the rate of fusion inside the protostar
D)   increase the temperature of the protostar

Question 5

What is the best evidence that giant molecular clouds formed through collisions of large gas flows?

Accepted Answer

A)   the Doppler shifts of segments of the clouds
B)   the balance between gravity and pressure in the clouds
C)   the long lifetimes of the clouds
D)   the magnetic field structure within clouds

Question 6

According to most astronomers,what two factors are necessary to launch a protostellar jet?

Accepted Answer

The answer of According to most astronomers,what two factors are...

Question 7

How do astronomers measure the properties of molecular clouds?

Accepted Answer

A)   through emission lines of H2
B)   through absorption lines of H2
C)   through emission lines of tracer molecules like CO2
D)   through interactions with nearby clouds

Question 8

The figure below shows the HR diagram for an astronomical object.What kind of object is it?

Accepted Answer

A)   an elliptical galaxy
B)   a spiral galaxy
C)   a globular cluster
D)   an open cluster

Question 9

Which regions of a molecular cloud collapse under gravity first?

Accepted Answer

A)   those with the smallest linear size
B)   the densest
C)   the least massive
D)   the most massive

Question 10

A protostar forming without magnetic fields will most likely lack:

Accepted Answer

A)   a molecular outflow.
B)   an accretion disk.
C)   an envelope.
D)   the conditions necessary for fusion.

Question 11

A gas cloud is in pressure equilibrium with its surroundings,which have a temperature of 10⁴ K.If the gas cloud is 100 times denser than the surrounding medium,what is its temperature?

Accepted Answer

A)   104 K
B)   1 K
C)   10 K
D)   100 K

Question 12

A T Tauri star is a:

Accepted Answer

A)   low-mass main sequence star.
B)   red giant star with strong winds.
C)   white dwarf that undergoes novae.
D)   protostar that produces X-ray flares.

Question 13

A star with which of the following masses is most likely to form in a molecular cloud?

Accepted Answer

A)   0.5 MSun
B)   1 MSun
C)   10 MSun
D)   100 MSun

Question 14

A massive protostar is more luminous than a low-mass protostar because it:

Accepted Answer

A)   undergoes a different set of fusion reactions.
B)   has a lower temperature.
C)   releases less of its thermal energy.
D)   had more potential gravitational energy before it collapsed.

Question 15

Which of the following helps support molecular clouds against gravitational collapse?

Accepted Answer

A)   thermal pressure
B)   turbulence
C)   magnetic fields
D)   all of the above

Question 16

Which of the following changes would help a molecular cloud to resist gravitational collapse longer?

Accepted Answer

A)   increasing the cloud's average velocity relative to the center of the Milky Way.
B)   decreasing the cloud's temperature
C)   decreasing the fraction of metals in the cloud
D)   changing the cloud's composition

Question 17

A gas cloud with a temperature of 100 K is embedded in a medium of temperature 3 × 10⁶ K and density 0.1 particle per cubic centimeter.If the gas cloud is neither expanding nor contracting,what is its density?

Accepted Answer

The answer of A gas cloud with a temperature of...

Question 18

What is the typical density of the interstellar medium?

Accepted Answer

A)   0 particles/cm3 (vacuum) 
B)   1 particle/cm3
C)   1012 particles/cm3
D)   1019 particles/cm3

Question 19

Astronomers have not found any stars more massive than about 125 MSᵤn in the Milky Way.What stops more massive stars from forming?

Accepted Answer

The answer of Astronomers have not found any stars more...

Question 20

Which of the following lists the phases of the interstellar medium in order,from densest to least dense?

Accepted Answer

A)   molecular clouds, H I clouds, H II regions, warm interstellar medium, coronal gas
B)   H II regions, warm interstellar gas, coronal gas, H I clouds, molecular gas
C)   molecular clouds, H II regions, coronal gas, warm interstellar gas, H I clouds
D)   H I clouds, molecular clouds, warm interstellar medium, H II regions, H I clouds, coronal gas

Exam 12: Nursery of the Stars: the Interstellar Medium and Star Formation