8&9 Low Mass And High Mass Stars Flashcards
What’s a low mass star? (In terms of mass)
Mass < 2 solar masses
How does fusion occur in low mass stars?
Fuses hydrogen into helium in its core via proton-proton chain (4 hydrogen to 1 helium)
How would we calculate energy generated in a fusion reaction?
Use mass différence and E=mc^2
Life time of a low mass star?
Billions of years ( 10 bill for solar mass star)
What happens when core hydrogen is exhausted?
-Core collapses and hydrogen shell burns around inert helium core
-photosphere expands becoming red giant
-helium is continually added to core and starts burning when T>100mil K
What happens when low mass star is in red giant phase and has exhausted all core helium? (Death of low mass star)
-3 Helium nuclei combine to form one carbon nucleus, so inert carbon core , temp rises and core expands
-double shell burns around inert carbon core (helium shell + carbon shell)
-carbon fusion/ burning can’t occur as T not >600 mil k
-outer layers ejected into space which create planetary nebulae
-démenant core is white dwarf
What is a planetary nebulae ?
-When stars eject outer layers into space Planetry nebulae formed
- huge shell of gas ionised by radiation making it glow brightly
-disappears
Where was most carbon in universe today formed?
Low mass stars
What is a high mass star ? In terms of mass ?
Mass > 8 solar masses
How are stars formed?
-Collapse of dense low pressure clouds when gravity overcomes thermal pressure
-compression gives rising temp and nuclear fusion occurs when T >10 mill k
What do we know about first stars?
-possible formed at start of universe
-almost entirely He and H
Relationship between mass/particle ration and energy in stars?
Mass/particle decrease releases energy
Mass/particle increase absorbs energy
How does hydrogen fusion occur in high mass stars? And why diffferent to low mass?
-CNO cycle ( 4H produce one He with a carbon catalyst
-more efficient than pp as carbon acts as a catalyst
What Life time do high mass stars have and why?
Very short, bc strong gravity so higher temp and rapid fusion rate
What happens in high mass star when core hydrogen is exhausted ?
-hydrogen burning around helium core, and outer layers expand producing super giant
-helium burning in core when T> 100 mil k so inert carbon core w double shell burning
-carbon fusion when T>600 k mil and burn around inert core
-core keeps shrinking and becomes hot for more fusion creating layers until core is full of iron and cannot fuse and release energy
