PX282 - E6 - higher mass stars

they evolve similarly to low-mass stars, up to AGB, but they burn faster with no helium flash

fusion can continue, potentially up to iron

C-burning

• temperature $\sim 6\times {10}^{8}K$
• forms Ne, Na and Mg
• lasts about $300$ years

O-burning

• a temperature $\sim {10}^{9}K$
• forms Si, P, S and Mg
• lasts about $200$ days

Si burning

• forms Fe,
• lasts about 2 days

a shell structure forms with an degenerate iron core

if the mass of the core goes above the chandrashekhar limit $(>1.4M_{\odot })$, it collapses, resulting in a supernova

this is a gravitational collapse, ie. a free fall timescale

as the inner core collapses, eventually the strong nuclear force causes a bounce-back

this causes a substantial energy release of $\sim {10}^{46}J$

about 1% of it is kinetic energy released as neutrinos in about $10s$

observationally, such core-collapse supernovae are labelled type $II$, $Ib$, $Ic$

the outer layers fall slower and they are suspended over the collapsing core

a lot happens in a short time

the core collapses in seconds, while the shockwave takes hours to reach the surface

a large quantity of $\alpha$-elements is produced