The resulting mass of the remnant of a core-collapse SN

[bendaten]

Hi,

This is my first post. If this question is already answered please direct me there. I don't know yet how to narrow my search in the forum.

If a core-collapse SN starts as soon as the degenerate core reaches Chandrasekhar limit and the outer boundary of that core is detached from the surrounding stellar material, then why do we have remnants of different masses after the stellar material is blown away? I would expect exactly 1.4 solar masses remnants.

Thanks,
Daniel

 

[Drakkith]

Hmm. Interesting question.
I'm not sure but I think it could have something to do with more massive cores also being bigger and fusing more material at any given moment than smaller cores. If these cores start to fuse elements into Nickel then before the fuel is burnt completely there will more mass in the bigger cores than the smaller ones. Once the fuel is burnt and the core runs out of energy to hold itself up against gravity it collapses, with the larger more massive cores collapsing into larger remnants.

However that's all my "best guess".

 

[bendaten]

Thanks Drakkith,
According to my understanding, there is nothing burning in the core - it is inert. The Silicon fusion happens in a shell around the core and its "ash" is added to the core until it reaches Chandrasekhar limit and collapses.
Therefore if the core is 1.4 solar masses and it collapses, separates from the rest of the stellar material, and blows it away, it would have stayed the same mass or lower.
However we "know" that more massive remnants exist so there should be a mechanism that draws more mass from the envelope during the collapse, or during the bouncing back, or even later. What is this mechanism?
Daniel

 

[Drakkith]

I'm not sure bendaten. I was under the impression that the core collapsed soon after turning all it's fuel into Nickel, regardless of the outer shells. Anyone else know?

 

[twofish-quant]

If a core-collapse SN starts as soon as the degenerate core reaches Chandrasekhar limit and the outer boundary of that core is detached from the surrounding stellar material

That actually isn't what happens. What happens is that lose pressure in the center of the star, and then the entire star starts to collapse. The inner core stops collapsing when neutron pressure kicks in, and then you have a shock wave that moves out. The shock wave starts at 0.8 solar mass, at about 1.2 solar masses it stalls, and then something magic happens to revive the shock.

How much of the star gets put in the remnant is an open question. We do know from observation that most of the inner core turns into the remnant. If you blasted much of the inner core, you end up with too many neutron-rich elements.

 

[twofish-quant]

Therefore if the core is 1.4 solar masses and it collapses, separates from the rest of the stellar material, and blows it away, it would have stayed the same mass or lower.

The whole star collapses. Once you kill pressure in the center, then gravity takes over, and gravity doesn't know what part of the star you are in.

However we "know" that more massive remnants exist so there should be a mechanism that draws more mass from the envelope during the collapse, or during the bouncing back, or even later. What is this mechanism?

Gravity. Getting higher masses into the core is easy. It's getting an explosion that's tough.

 

[bendaten]

Hi twofish-quant,
Thanks for your reply.
Why would the entire star collapse at the same speed? The shells around the core are still burning Si and lighter fuels up until H. There is still pressure there. Although the pressure below them has suddenly vanished, I would expect them to collapse much slower then 0.23c and get detached from the inner core. So what happens that sucks all that material in?

 

[twofish-quant]

Why would the entire star collapse at the same speed?

They wouldn't. What ends up happening is that once the center of the pressure goes to zero, the information that it's gone to zero goes through the star at the speed of sound.

The shells around the core are still burning Si and lighter fuels up until H. There is still pressure there. Although the pressure below them has suddenly vanished, I would expect them to collapse much slower then 0.23c and get detached from the inner core.

That actually doesn't happen. One way of imaging it is imagine that you sitting on an air cushion on top of a floor. The air cushion provides pressure that keeps you from hitting the floor.

Now imagine that a hole opens up. The air cushion is still exerting pressure on you, but it doesn't matter because once the floor disappears, both you and the air cushion are going to floor through the hole. Once the pressure at the bottom disappears, it doesn't matter how much pressure there is in the middle, you are going to drop.

To put it in more technical terms. What matters is not P, but the difference in pressure between two spots dP/dr. If you are in an air cushion and a hole opens up underneath you, the pressure of the air cushion doesn't change much, but because the pressure at the bottom of the cushion is now zero, you are going to drop.

So what happens that sucks all that material in?

It's not sucking, but falling.

 

[Chronos]

Core collapse is a complicated process. Predicting the remnant mass of a supernova is more sorcery than science.

 

[twofish-quant]

Core collapse is a complicated process.

The collapse part is easy. It's the "go boom" part that's messy.

Predicting the remnant mass of a supernova is more sorcery than science.

It really can't be done with our current state of knowledge.

 

[bendaten]

Hi twofish-quant,
Thanks for your explanation. I really liked your air-cushion analogy.
So what I understand is that the entire star is collapsing, once the inner part gets to a neutron degeneracy state it starts bouncing back, creating a shock wave that propagates out while more matter rushes in. At some point the outward propagation of the shock wave is stalled (by the collapsing matter?) and current models do not explain what resumes the wave that eventually cause the SN explosion. I saw that they have several hypotheses such as outward neutrino flux interacting with the in falling matter. In any case the amount of material left in the core (which determines the fate of the star, neutron star, BH) depends on the balance between the collapse and the shock wave, which we don't know yet.
Did I get it right?