Question

What is the exact mechanism by which an implosion of a dying star becomes an explosion?

I'm not positive that this is the correct section, but I couldn't find anywhere else that'd better suit the question.

Answer 1

I think the implosion is set off when gravity starts winning, but then as the core shrinks things get too heated up..and the atoms get huge amount of kinetic energy.. such that they finally explode :P

Answer 2

For better information: Google up "Chendrasekhar limit", which deals with the aging of stars and at what conditions, a star would become a 'SUPERNOVA'....

Answer 3

The thing that wonders me is... Even if the atoms gain so so much kinetic energy, why would it explode? I mean why not just increase more and more and something else happens why explode :P ?

Answer 4

Ok a couple of things:
1. The Chandrasekhar limit applies only to specific rare supernovae called type Ia, where a white dwarf (dead low mass star) accretes further mass from a binary companion and exceeds the mass of 1.4 times that of the Sun.
2. General core collapse supernovae occur in stars which were born around 8 times the mass of our Sun. Upon fusing heavier and heavier elements in the core, (to keep the star 'inflated' by radiation pressure against gravity trying to crush it) eventually an iron core is formed. This cannot be fused and so there is a catastrophic collapse when gravity completely overwhelms the now tiny radiation pressure. The entire outer layers of the star fall in seconds (the implosion) and crucially REBOUND off the dense iron core, producing and 'ex'-plosion. This is the currently accepted theory.

Answer 5

for massive stars, more than 10 solar masses, after the formation of an Iron core, fusion cannot generate more energy as Iron requires energy to fuse. Hence gravity takes over. Finally, the contraction of the mass gets to a stage where the atoms in the core break down into protons and neutrons and the protons convert to neutrons. Finally, the core is a mind boggingly dense body of degenerate neutrons. The contraction finally reaches a stage where the neutrons come so close, they essentially touch each other. This produces a rebounce, which is conveyed to the upper shells as massive shock waves resulting in a gigantic explosion, the likes of which a galaxy would remember. The entire out mass of the star gets exploded in this rebounce as a supernova explosion. This is the brightest event in the whole galaxy.
What remains is the core of degenerate neutrons which then again has 2 choices based on its mass.
If the mass is less than 2 solar masses, the pressure due to the dense degenerate neutrons balances gravity and we get a pulsating neutron star.
If the mass is more, neutrons lose, a final contraction takes over sucking everythinng into a singularity. gravity wins. A Blackhole forms.