Download STUDY GUIDE FOR CHAPTER 1

STUDY GUIDE FOR CHAPTER 12
The following is a list of topics and subtopics along with some questions and explanations.
I.
Basics
A.
B.
C.
D.
E.
Pressure versus gravity
You can get pressure in a star either through heat or through degeneracy pressure.
What ways can you generate heat in a star to keep the pressure up?
What happens to nuclear fusion rates as the temperature increases?
Why do more massive stars go through each phase of their life in a shorter time than less
massive stars?
F. What is electron degeneracy pressure? Why will it only hold up a star with mass less than
1.4 MSun?
II.
A.
B.
C.
D.
III.
Star formation
You should understand what stars form out of and how they are formed.
What is the source of energy for a protostar?
When does a protostar become a main sequence star?
Why does a brown dwarf not ever become a main sequence star?
Main Sequence Phase
A. Why do more massive stars have higher luminosity’s while on the main sequence than less
massive stars do? How is this related to the shorter amount of time they spend on the main
sequence?
B. What are stars doing to generate energy while they are on the main sequence?
C. Stars very gradually become more luminous while they are on the main sequence. Why is
this the case?
D. When does a star leave the main sequence?
IV.
Old Age and Death of Small and Intermediate Mass Stars
A. Lowest mass stars burn most of their H to He and then become white dwarf stars.
B. For stars with 0.4 MSun < M < 8 MSun the phases are:
1. Red giant phase
2. Helium burning phase
3. Double shell burning phase
4. Planetary nebula phase
5. White dwarf phase
You should know the name of each phase, what is going on with the star’s core and outer layers
in that phase and why
V.
High mass stars
A. They go through first red giant, helium burning in the core, and double shell burning phases.
B. Then they go through a sequence of situations where the core is contracting and heating up
when no fusion is going on inside it and then stops contracting when the next type of fusion
begins. Meanwhile the outer layers expand and cool while the core contracts. They
contract and heat up when the core stops contracting.
C. Eventually you get an iron core.
D. It contracts until it is held up by electron degeneracy pressure.
E. Then when it gets larger than 1.4 times the mass of the Sun it collapses and you get a
supernova type II explosion. You should know the details of how and why this occurs.
You should also distinguish between this type of supernova explosion and a type Ia.
VI.
Very high mass stars
A. These go through all the stages that high mass stars do including the collapse of the iron
core and the generation of a shock wave.
B. However the outer layers of the star are thought to have so much material in them that they
can absorb the shock wave and the star does not blow up.
C. The core consists of neutrons held up by neutron degeneracy pressure.
D. As material from the outer layers falls on the core eventually it gets so massive that neutron
degeneracy pressure cannot hold it up.
E. Then it collapses and becomes a black hole.
F. As the rest of the outer layers of the star fall onto the black hole they form an accretion
disk.
G. It is possible that jets of material may be shot in opposite directions perpendicular to the
accretion disk at very high energy. Collisions of the particles can produce electrons and
positrons which then annihilate to form gamma ray photons. This is called a hypernova.
We are not certain these occur but there is evidence from gamma ray bursters that they do.