Assignment #8 (Chapter 16 in the 4th edition of Bennett et al.)

Read Chapter 16

1.) What is a molecular cloud?

2.) At the beginning of the star formation process, the material that stars eventually form from is:
a.) interstellar gas
b.) relatively dense (density greater than or equal to 300 particles/cm³)
c.) cold (T < 50 K)
d.) all of the above
e.) none of the above

3.) During the star formation process, what happens to the material from which the star eventually forms:
a.) gravity tries to make the clump of material contract
b.) thermal pressure tries to make the clump of material expand
c.) sometimes the clump of material cools down by radiating photons
d.) all of the above
e.) none of the above

4.) Compare the number of initial star forming cloud(s) with the number of star(s) formed:
a.) usually, multiple stars are formed from a single cloud
b.) usually, a single star is formed from a single cloud
c.) usually, multiple clouds combine to form a single star

5.) Consider the dense cloud core that will evolve into a star. While it is collapsing, what what happens to its rotation speed?

6.) What is a protostellar disk?
a.) a wind of material that flows out from a protostar
b.) one of many lumps of material that prevent radiation from leaving the protostar
c.) the portion of a star forming cloud where most of the protostars reside
d.) none of the above

7.) When do stars like the Sun begin to fuse hydrogen into helium:
a.) about the time that the birth cloud begins to contract
b.) about the time that the protostar fires a jet
c.) about the time that the protostar's surface temperature reaches 3000 K
d.) none of the above

8.) Brown dwarfs:
a.) are white dwarfs that have cooled down
b.) are very low mass stars that only started nuclear burning recently
c.) will never fuse hydrogen into helium
d.) all of the above
e.) none of the above

9.) Why is it impossible to make a star with a mass over 200 x M_Sun in the modern universe?
a.) electron degeneracy pressure prevents the protostar from collapsing enough
b.) nuclear burning is not possible when the temperature in the protostar's center is too high
c.) the pressure of photons leaving the star is great enough to blow off some of the material
d.) all of the above
e.) none of the above

10.) (Problem adapted from textbook:) " Briefly describe
the process by which a protostar and protostellar disk form from gas in a molecular cloud".