9. Just stars

Question 1

birth of a star

Answer 1

1. stellar nebula
2. gravitational force pulls in material
3. more material more grav force

repeat

4. dense core has high temperature and high pressure
5. hydrogen overcomes electrostatic repulsion & fuses
6. protostar

Question 2

how does a protostar go into main sequence

Answer 2

1. the material forms a spherical atmosphere
2. the core keeps on fusing

Question 3

how does a star stay in main sequence

Answer 3

the atmosphere is pulled in by weight
the atmosphere is pushed out by fusion pressure

Question 4

death of a star (hydrogen shell burning)

Answer 4

1. core runs out of H
2. core contracts
3. fusion pressure decreases
4. atmosphere pulled in
5. fusion pressure increases
6. fusion pressure > weight
7. expands and cools

Question 5

death of a red giant

Answer 5

1. red giant keeps expanding
2. fusion diminishes
3. heavier elements form (Fe and lower)
4. fusion pressure decreases
5. atmosphere collapses and rebounds from core
6. material thrown out into space (forms a planetary nebula)
7. core gets left behind and keeps fusing (white giant)

Question 6

death of a big star

Answer 6

1. core runs out of H
2. fusion pressure decreases
3. atmosphere collapses
4. elements heavier than Fe are produced
5. force of collapse > electron degeneracy pressure
6. core collapses
7. outer layers rebound from core @ high velocity
8. huge shockwave (supernova)

Question 7

< 1.43MSUN

Answer 7

neutron star aka pulsar

• core particles get forced together into densely packed neutrons
• 20km diameter
• so dense that the only radiation is from the axis of rotation (radio waves)

Question 8

< 1.43MSUN

Answer 8

black hole

• core continues collapsing into an infinitely dense point (singularity)
• event horizon around black hole
• all objects in the EH would need to be > speed of light (300 000 000 m/s) to escape