Question: What would happen if a star imploded?

Sarah Casewell answered on 16 Jun 2014:

This is what happens when a star dies. All the helium that is produced when hydrogen is burned, ends up in the core of the star. This can also be burned into heavier elements like carbon, oxygen and nitrogen.
All this stays in the core until the star can’t burn anything else. Then the outer layers of the star all fall inwards, pulled by gravity.
In most stars, the core gets squeezed until about the mass of the sun is in the core, and then all the outer layers of the stars fall into it. The core can’t get squished any more though, so the gas hits it and rebounds back into space – this is a planetary nebula (google ring nebula for a picture – you can see this on a clear night with a good telescope in your back garden). The hot core that is left is the white dwarf.

This happens in most stars, but if you have a massive star – more than 8 times the mass of the sun, then the core can get squeezed even further – all the protons and electrons are squeezed together into neutrons and you have a neutron star or if the star is really massive, a black hole! The explosion when the outer layers of the star are blown off are called supernovae in this case, and all the heavy elements in the universe (more massive than iron) are formed in these explosions!