Chapter 17- Post Main Sequence Evolution of Stars

Question 1

What happens to the H when in the star

Answer 1

it will eventually run out

Question 2

Core Hydrogen burning phase

Answer 2

• pressure drops due to conversion of H to He
• core contracts to make up for loss of pressure
• contraction cause temp to increase
• this causes fusion and luminosity to increase

Question 3

where does star go after MS on HR diagram

Answer 3

to the up left

Question 4

what happens when a star can no longer fuse H and He together in its core

Answer 4

the core shrinks and heats up

Question 5

what is lifetime

Answer 5

energy over luminosity

Question 6

radiation pressure

Answer 6

• the main source of pressure in the sun today
• aka photons colliding with gas
• photons come from thermonuclear fusion (energy)

Question 7

hydrogen shell burning

Answer 7

• when the entire core is converted to helium
• and thermonuclear fusion stops in the core
• star LEAVES the Main sequence

Question 8

when the core collapses

Answer 8

star gets hotter

Question 9

when the outer layers expand

Answer 9

star gets cooler

Question 10

what causes the RED GIANT phase

Answer 10

when the core collapses and outer layers expand

Question 11

what does a star do to compensate for getting colder

Answer 11

gets larger

Question 12

core helium burning

Answer 12

eventually the core temp becomes high enough to ignite fusion of He

Question 13

why is helium harder to fuse/burn

Answer 13

He is heavier and has more protons, causing them an unattractive from each other and can’t fuse properly

Question 14

what are the basic steps after leaving MS

Answer 14

• Main sequence
• Red Giant
• He Flash
• Horizontal branch
• Asymptotic giant branch
• Planetary nebula

Question 15

horizontal branch

Answer 15

• stars start to move left on the HR diagram

- after He flash in tight up-hand corner

Question 16

Asymptotic giant branch

Answer 16

• carbon and oxygen core
• no core He fusion
• core collapses
• outer layers expand and cool
• He/H shell burner

Question 17

thermal pulses

Answer 17

• driven by repeated He shell flashes

- heats up and cools down over and over

Question 18

Planetary Nebula

Answer 18

• outer layers thrown off by ejection of H and He into space
• last phase of star like out sun
• a white dwarf core is left behind

Question 19

what happens when the stars core runs out of helium

Answer 19

Helium fuses in a shell around the core

Question 20

what is the death of a massive star like

Answer 20

• high mass stars fuse at a higher rate causing a much higher temp
• the high temp allows He to fuse with heavier elements
• turns into Iron and then stops because iron has the highest binding energy of any nucleus
• then gets stuck
• when fusion stops, star will contract and heat up

Question 21

finale of massive star death

Answer 21

multiple shell burning- when many shells of elements are burning and looks like an onion