Super novae mechanics - how does it work?

[lavinia]

I was watching a popular TV series on the Universe which briefly described super novae.

Here are two naive questions not well answered in the video.

1) When a white dwarf becomes a super nova through accretion of gas from a companion star. the pressure from the accreted material ignites carbon-carbon fusion which explodes the star into a super nova. Why does this carbon-carbon fusion release so much energy and blow the star?

2) For huge stars carbon-carbon fusion apparently is no problem and in fact fusion is able to form elements all the way up to iron. At some point the iron core implodes from its own weight.
Why is this? Is this saying that if one builds up an iron ball in space - slowly adding more iron - until the ball is enormous that at some point it will no be able to support itself? Secondly, why is the implosion so violent and where does the energy come from?

 

[SteamKing]

This article explains in more detail the mechanics of SN formation:

https://en.wikipedia.org/wiki/Supernova

1) Briefly, the WD exceeds the Chandrasekhar mass limit due to the accretion of gas from the companion star. The WD is no longer able to support its structure against gravity and collapses. The collapse causes the C-C fusion reaction, which takes place in a matter of seconds. The sudden release of this energy in a short amount of time causes the WD to disperse violently.

2) In a core collapse SN, the iron core is enclosed in layers of other fusion products, with hydrogen forming the outermost layer, followed by helium, etc., until the iron is at the center. Iron is incapable of generating energy by fusion and thus cannot support itself against gravity. In a matter of milliseconds, the iron core collapses, with the outer layer rushing in on itself at a substantial fraction of the speed of light. The rest of the star is momentarily suspended while the core collapse takes place. If the core is too massive, a black hole forms. If the core is not massive enough to form a black hole, a neutron star will form. When the outer layers of the star hit the surface of the neutron star, a shock wave is formed which ejects this material into space. Additional heat from the collapse causes further fusion reactions in the outer layers.

 

[lavinia]

This article explains in more detail the mechanics of SN formation:

https://en.wikipedia.org/wiki/Supernova

1) Briefly, the WD exceeds the Chandrasekhar mass limit due to the accretion of gas from the companion star. The WD is no longer able to support its structure against gravity and collapses. The collapse causes the C-C fusion reaction, which takes place in a matter of seconds. The sudden release of this energy in a short amount of time causes the WD to disperse violently.

2) In a core collapse SN, the iron core is enclosed in layers of other fusion products, with hydrogen forming the outermost layer, followed by helium, etc., until the iron is at the center. Iron is incapable of generating energy by fusion and thus cannot support itself against gravity. In a matter of milliseconds, the iron core collapses, with the outer layer rushing in on itself at a substantial fraction of the speed of light. The rest of the star is momentarily suspended while the core collapse takes place. If the core is too massive, a black hole forms. If the core is not massive enough to form a black hole, a neutron star will form. When the outer layers of the star hit the surface of the neutron star, a shock wave is formed which ejects this material into space. Additional heat from the collapse causes further fusion reactions in the outer layers.

Lovely. Thank you.

 

[Chronos]

The mass of the core of a core collapse supernova is rather uncertain. Assuming it is no more than the Chandrasekhar mass [which seems reasonable], it may be difficult for the remnant to directly form a black hole without fallback of sufficient mass to exceed neutron degeneracy pressure of the remnant. In theory, any star exceeding 20 solar masses should form a black hole, yet, we have evidence of significantly more massive progenitors that left a neutron star remnant [e.g., The most massive progenitors of neutron stars: CXO J164710.2-455216, http://arxiv.org/abs/0804.4143] . Another possibility is stars that bypass the supernova phase and collapse directly into a black hole [re: Mass Limits For Black Hole Formation, http://arxiv.org/abs/astro-ph/9902315: A Survey About Nothing: Monitoring a Million Supergiants for Failed Supernovae, http://arxiv.org/abs/0802.0456 ]. This may explain the apparent mass gap between the most massive neutron stars and the least massive black holes [re: The Mass Distribution of Stellar-Mass Black Holes, http://arxiv.org/abs/1011.1459: Missing Black Holes Unveil The Supernova Explosion Mechanism, http://arxiv.org/abs/1110.1635] .

 

[SteamKing]

Only the survey paper has a good link; all of the others give a 'Bad Paper Indentifier' message.

 

[Spourk]

Only the survey paper has a good link; all of the others give a 'Bad Paper Indentifier' message.

Remove the colons/brackets at the end of the links, they are glitchy.