I What is the current understanding of supernova mechanisms in 2020?

[virgil1612]

TL;DR Summary

Current status-quo?

Hello,

Could someone explain or post some links for the current status-quo of the mechanisms that make a massive star explode?I know that the prompt mechanism doesn't work, that the shock stalls and must be revived by something (neutrinos, presumably), but where are they (the researchers) as of today? Can they finally make their stars explode in their simulations?

Thanks, Virgil.

 

[stefan r]

I liked the physics girl episode [video] where she explains it.

 

[alantheastronomer]

I liked the physics girl episode [video] where she explains it.

The physics girl's analogy is better suited to the collision between a proton and an electron - it fails when describing a supernova explosion, because the stellar core is only one and a half solar masses while the envelope bearing down on it is ten, so it's more like having the basketball bouncing off of the tennis ball...no wonder the simulations fail! In any case I think Virgil is looking for a slightly more sophisticated answer since he mentions the prompt shock stalling and the possibility of it being revived by neutrinos.
Turns out the neutrinos don't diffuse out fast enough to revive the shock, but soften the infall instead. Recently it's been discovered that convection might give the neutrinos and the shock enough energy, as convection helps transport the neutrinos faster than diffusion could, and the additional velocity provided by the convection helps strengthen the shock. There's a very thorough but technical discussion by Tony Mezzacappa of Oak Ridge National Lab on the UC-HiPACC youtube channel from 2014 entitled Contemporary Core Collapse Supernova Theory.

 

[stefan r]

The physics girl's analogy is better suited to the collision between a proton and an electron - it fails when describing a supernova explosion, because the stellar core is only one and a half solar masses while the envelope bearing down on it is ten, so it's more like having the basketball bouncing off of the tennis ball...

The analogy is just there to explain how a collapse inward to a lower part of a gravity well can also cause mass to burst up out of the gravity well.

Gravity is inverse distance squared. Gravitational binding energy is proportional to 1/radius. When bouncing a basketball a meter or so high Earth's gravity is very nearly constant. Falling from white dwarf size to neutron star size the radius changes by a less than 1000x but at least several hundred. That is enough excess bounce. A basketball has only 250 times the mass of a pingpong ball.

 

[alantheastronomer]

The analogy is just there to explain how a collapse inward to a lower part of a gravity well can also cause mass to burst up out of the gravity well.

Yes but the analogy is misleading because it requires the transfer of momentum from a larger mass to a smaller one in order to get a larger recoil velocity...and the analogy is even less appropriate for a realistic supernova explosion because in the real life situation the collision is inelastic, a large portion of the energy goes into heating instead of kinetic motion.

 

[256bits]

Yes but the analogy is misleading because it requires the transfer of momentum from a larger mass to a smaller one in order to get a larger recoil velocity...and the analogy is even less appropriate for a realistic supernova explosion because in the real life situation the collision is inelastic, a large portion of the energy goes into heating instead of kinetic motion.

Not sure if I understand that.
A gas collapses radially towards its centre of mass. Whether or not there is anything there at that area such as a core of a star would seem irrelevant, except that the core can compress and provide an outward push on rebound. Much as will the collapsing gas, will over-compress and rebound, perhaps sending the outer layers beyond that from which they started.
I think the problem is, is why so much of the star mass rebounds, isn't it?

 

[alantheastronomer]

Not sure if I understand that.

Not trying to be dismissive, but if that's the case can I suggest you look up the following terms?: conservation of linear momentum; elastic and inelastic collisions; ideal gas law; core collapse supernovae

except that the core can compress and provide an outward push on rebound

a neutron star stellar core is very rigid and does not compress...or rebound!

I think the problem is, is why so much of the star mass rebounds, isn't it?

Yes, in the sense that even our best, most sophisticated models fail to produce an explosion - so just how it happens is still a mystery!

 

[256bits]

a neutron star stellar core is very rigid and does not compress...or rebound!

quite true.
I was thinking the outer remnants of the iron core before it ( is it 100% conversion or is some of the iron blown off also ) is converted to neutrons, which would not happen instantaneously throughout.

Not trying to be dismissive, but if that's the case can I suggest you look up the following terms?: conservation of linear momentum; elastic and inelastic collisions; ideal gas law; core collapse supernovae

A short list for anyone to start off with. Mostly at B level.
Most of the 'basic' explanations just talk about core collapse and rebound, which doesn't say much.
Sometimes something about neutrino production.
Anyone looking and finding results, and not going further, would fail to surmise that there is something amiss.

i would suggest someone looking into this, also investigate the Chandrasekhar limit.
https://en.wikipedia.org/wiki/Chandrasekhar_limit
as that is what is at the centre of a star going type two nova.