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Supernova
Carbon Fusion
• At 15 MK carbon can fuse
with four hydrogen nuclei to
create more helium.
carbon-12
photons and
neutrinos
• At 100 MK carbon can
directly fuse with helium to
form oxygen.
• Both processes release
photons.
carbon-12
oxygen-16
Core Fusion
• High mass stars continue
beyond helium and carbon
fusion.
– Higher temperatures
– Higher pressures
– Deeper layers
• Iron is stable and doesn’t
fuse without massive
added energy.
Fusion steps
 Hydrogen to helium
 Helium to carbon
 Carbon to oxygen
 Oxygen to neon
 Neon to silicon
 Silicon to iron
Degenerate electrons
• The nuclei from fusion are separated from their electrons.
– Very close degenerate electrons
• During core fusion degenerate electrons build up.
– Electric charge opposes gravity
– Opposing forces create enormous stress
inward
force of
gravity
outward
force of
electrons
Death of Supergiants
-20
supernovae
-15
Abs. Magnitude
-10
-5
0
5
Sun
• A supergiant changes
temperature becoming
more luminous.
– More than 8 M
– Core collapses more
– Charge loses to gravity
10
15
20
O B A F G K M
Spectral Type
• This becomes a type II
supernova.
Stellar Explosion
• When gravitational force
exceeds the electron
repulsion, the core
collapses immediately.
– Energy in photons and
neutrinos
• The outward energy hits
collapsing material and
the star explodes.
Binary Explosions
• A binary can transfer gas from a giant to a white dwarf.
– Increases white dwarf size
– Gravity exceeds electron repulsion
• It will explode into a type I supernova.
– Brighter than type II
white
dwarf
giant star
gas pulled
to partner
supernova
Supernova Remnants
• The supernova core collapse
is at 200 billion K.
– Photon energies enough to
break up iron nuclei
• Broken nuclei fuse with iron
to create heavy elements.
• This matter goes to form
new stars and planets.