The Lives and
Deaths of Stars
SESAME Astronomy Winer 2011
Week 6?
Review of Star
Gas Formation
clouds begin to collapse
Gas heats up, spins faster
In the meantime:
bits of dust and rock and ice are
sticking together and forming
planets
these planets kick out the last
balls of ice in their orbits
fusion starts in the densest
part
(maybe*)
*if it doesn’t, we don’t call it a star
fusio
2 protons come close together, one
turns into a neutron, they stick together,
nforming Deuterium (total proton count
so far = 2)
this deuterium nucleus collides with
another proton, forming Helium-3 (total
proton count so far = 3)
These 2 steps occur many many times
per second (total proton count = 6)
2 Helium nuclei collide, forming Helium4 and emitting 2 protons (total proton
Live* Stars
wide range of masses: 0.08
M to about 120 M
“high-mass” M > 8M and
“low-mass” < 8 M
⊙
⊙
⊙
⊙
lower mass
higher mass
higher Temperature->brighter,
Temperature->fainter, longer lived, redder
shorter lived, bluer
smaller Radius
larger Radius
CNO Cycle
comparison of
efficiencies
leaving the main
sequence
evolution of a lowmass star
ome clusters
initial mass
function
evolved cluster
evolution of a
cluster
other evolved
cluster
evolution of a lowmass star