Type Ia supernova:
Dense white dwarf attracts some of the material from companion start and mass of white dwarf increases. After it compresses and heats up. Fusion reactions start when mass gets close to chandrasekhar limit at 1.38m.
So much energy is released that entire system is disrupted in a gigantic explosion (Type Ia supernova).
Note: no hydrogen spectral lines in spectrum of type Ia supernova.
Due to high luminosity can see easily at very large distance. They all have the same luminosity.
Then we can use
[pic 1]
To find their distance d. This method is used to find the distances of the most distant galaxies.
The life story of a high mass star (m>8m.):
Because of their high mass all stages last a shorter period of time.
Protostar stage (the star contracts quickly because it has a high mass), main sequence life (m/l)
[pic 2]
Because of a very high mass the helium core is compressed and heated right away and the fusion of 4He into 12C and 16O proceeds without a pause (no first red giant stage).
Nucleosynthesis: formation of heavier nuclei by fusion of the lighter nuclei.
[pic 3]
Each fusion reaction releases less energy than the previous one and the rate at which the nuclear fuel is used increases with the mass of the nuclei that make up the fuel.
A mature supergiant near the end of its life:
[pic 4]
Lec 11 Type II Supernova
[pic 5]
The energy is released (they are exothermic reactions).
To fuse the nuclei heavier than iron (e.g. silver & gold) the energy must be supplied (the endothermic reactions).
The reason for that is that the binding energy per nucleon (proton or neutron) is the highest for iron.