What is the beginning of the end for main sequence stars?
1 Answer
The beginning of the end for a main sequence star is when the core runs out of fuel for the fusion process.
Explanation:
Main sequence stars are in a state of hydrostatic equilibrium where the outward pressure resulting from fusion reactions stops the core from collapsing under gravity.
The end process is different for smaller stars than it is for larger stars.
It the star is less than 8 solar masses, the beginning of the end occurs when the core runs out of Hydrogen. The core collapses until it is hot enough for Helium fusion to take place. This starts the red giant phase taking the star off the main sequence.
If the star is more than 8 solar masses, the transition from Hydrogen to Helium fusion to Carbon fusion and beyond happens seamlessly. When the core is predominantly Iron, then fusion requires energy rather than producing energy. This is the beginning of what will be a very violent end for the star. Once the core is mainly iron it will collapse under gravity and then the star will explode as a supernova. The stellar core will then become either a neutron star or a black hole.
