Chapter 17- Post Main Sequence Evolution of Stars Flashcards
What happens to the H when in the star
it will eventually run out
Core Hydrogen burning phase
- 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
where does star go after MS on HR diagram
to the up left
what happens when a star can no longer fuse H and He together in its core
the core shrinks and heats up
what is lifetime
energy over luminosity
radiation pressure
- the main source of pressure in the sun today
- aka photons colliding with gas
- photons come from thermonuclear fusion (energy)
hydrogen shell burning
- when the entire core is converted to helium
- and thermonuclear fusion stops in the core
- star LEAVES the Main sequence
when the core collapses
star gets hotter
when the outer layers expand
star gets cooler
what causes the RED GIANT phase
when the core collapses and outer layers expand
what does a star do to compensate for getting colder
gets larger
core helium burning
eventually the core temp becomes high enough to ignite fusion of He
why is helium harder to fuse/burn
He is heavier and has more protons, causing them an unattractive from each other and can’t fuse properly
what are the basic steps after leaving MS
- Main sequence
- Red Giant
- He Flash
- Horizontal branch
- Asymptotic giant branch
- Planetary nebula
horizontal branch
- stars start to move left on the HR diagram
- after He flash in tight up-hand corner
Asymptotic giant branch
- carbon and oxygen core
- no core He fusion
- core collapses
- outer layers expand and cool
- He/H shell burner
thermal pulses
- driven by repeated He shell flashes
- heats up and cools down over and over
Planetary Nebula
- 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
what happens when the stars core runs out of helium
Helium fuses in a shell around the core
what is the death of a massive star like
- 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
finale of massive star death
multiple shell burning- when many shells of elements are burning and looks like an onion
