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Stellar evolution - Coggle Diagram
Stellar evolution
Star's mass determines its evolutionary path
Chandrasekhar limit: .Provided the mass of the core is less than about 1,4 solar masses – the star will become a stable white dwarf.
Oppenheimer–Volkoff limit: Provided the mass of the core is not more than about 2–3 solar masses the star will become a neutron star.
Changes in nucleosynthesis
Star with mass less than 8 solar masses
In low-mass stars, helium collects in the core of the star, surrounded by a thin shell of hydrogen and a bigger hydrogen envelope. Both H and He fuse causing a release of energy that is called a planetary nebula that increases the star’s size when it cannot fuse elements heavier than oxygen.
The star then leaves the main sequence due to increase in size and becomes a red giant.
The star gets bigger and cooler on the surface.
The path then takes the star to the white dwarf region.
The star is now a stable but dead star with no nuclear reactions taking place in the core and will cool down to the background temperature.
HR-diagram
Star with mass more than 8 solar masses
The process begins much the same way as it did for low-mass stars, but differences begin to show when carbon fuses with helium in the core to form oxygen.
If the mass of the star is large enough, the pressure caused by gravity is enough to raise the temperature sufficiently to allow the formation of ever-heavier elements: neon, more oxygen, magnesium and then silicon; eventually, iron is produced in the most massive stars, and that is where the process stops since iron is near the peak of the binding energy curve.
The star moves away from the main sequence and into the red supergiant area.
The star is very hot in the core and photons are able to rip nuclei apart so that the core eventually only consists of neutrons.
The star contracts rapidly and then rebounds with an enormous shockwave - a supernova.
The core that is left behind, which is more massive than the Chandrasekhar limit, will most likely become a neutron star.
Neutron pressure keeps such a star stable, provided the mass of the core is not more than about 2–3 solar masses – the Oppenheimer–Volkoff limit.
If its mass is higher than this, it may collapse further and become a black hole.
HR-diagram
Evolutionary paths
