Massive star end.

vanesch

I have a (probably elementary) question about the end of a massive star. I know that the two issues are a neutron star and a black hole, depending on the remaining mass of the core.

In as much as I understand things, a type II supernova results from the sudden halting of the collapse of the core after the Chandrasekar limit has been passed and most protons recombined with electrons to make neutrons. Neutron degeneracy brings this collapse to a sudden end, and this sends out a powerful shockwave (together with a neutrino pulse) through the outer layers, giving rise to the massive energy release and blasting of material in the supernova.

However, when the limit of neutron degeneracy is reached (I think around 2.5 solar masses for the core), this doesn't stop the collapse and we are supposed to end up with a black hole.

Now, my question is: do we still have a supernova when there's a black hole formation ? Because there's not going to be a shockwave now, no ? There are probably still the neutrino's because I guess they get out before the black hole forms (not sure). That's maybe sufficient. But I thought that the main cause of a supernova was the sudden halting of the inward collapse of the outer layers, giving rise to a shock wave - halting which is, if I understand correctly, absent in the case of a BH. So is there nevertheless a supernova ? Or does the star silently go "poof" into a black hole ?

phyzguy

The exact details of what happens at the end of life of a massive star are still the subject of active research, and I think there is still controversy. However, according to presentations I have seen by experts doing these simulations, it appears that a "proto-neutron-star" always forms, halting the collapse and launching a shock wave outward. The proto-neutron star halts the collapse because the equation of state of the nuclear matter is so much "stiffer" than that of ordinary matter. If the star is massive enough, the material that continues to fall onto this proto-neutron star eventually pushes it above the limit of stability, and it collapses into a black hole. Otherwise, the neutron star remains intact. The current puzzle is how the shock wave makes it out of the star, since many simulations show that the shock wave "stalls" and isn't capable of blowing the start apart. This is where a lot of the current research and uncertainty lies.

HossamCFD

The question of the OP, and Core collapse supernovas in general have puzzled me a lot. The "proto-neutron-star" explanation is quite reasonable. I wonder if you can cite any reference so that I can check it.


Could the neutrino release be responsible for that ?

one last question: are there any significant role for the magnetic fields to play in core collapse supernovas ?

twofish-quant

Did my Ph.D. dissertation on this. The basic answer is that we don't know.

We think we more or less causes type II supernova. The problem is that we don't understand the details of the process, so we don't know if you can have an explosion and then a black hole.

And then mumble, mumble, mumble you get an explosion. The mumble, mumble, mumble may have something to do with magnetic fields, convention, multi-dimensional effects, or possibly unknown particles. It's an area of active research, but last I checked, we don't know although people have been doing some interesting things with multi-d calculations.

Check back in a year :-) :-)

Good question.

twofish-quant

The shock stalls, and then something weird happens.

The basic problem is that you have this massive amount of neutrino energy that leaves the star. If you can trap 1% of the energy, you have an explosion. The trouble is that neutrinos tend to go through everything so trapping 1% of the energy of the neutrinos turns out to be very difficult.

twofish-quant

Neutrinos has something to do with it. Exactly how they have something to do with the explosion people aren't sure.

Maybe :-) :-) :-)

twofish-quant

Also by a weird and wacky coincidence. The mathematics of how neutrinos flow through a supernova just happens to be the same as how stock prices change over time. Imagine the neutrino bouncing up and down as it leaves the star. Now imagine a basket of stocks with prices bouncing up and down.

Same math.

vanesch

Mmm, that's the most convincing way to tell me that people don't know

phyzguy

The talk I saw was by Christian Ott from Caltech, and it was at the APS meeting in Wash DC in Jan, 2010. He and his group have a lot of papers on this topic - one good one to start with might be:

http://arxiv.org/abs/0907.4043

They also have a web site at www.stellarcollapse.org that has a lot of useful information.

twofish-quant

One thing that's amusing thing that's not obvious unless you read the paper carefully is that they don't get an explosion. :-) :-) :-)

But the are doing a pretty good job of turning lemons into lemonade. They are converting their code to use GR. It turns out that GR really isn't that relevant in getting a supernova explosion, but since they aren't getting those, what they are doing is to focus on the collapse itself and trying to get gravity wave predictions.

This is pretty important because if a supernova goes off in our galaxy then we ought to be able to see the gravity waves from it, and some predictions on what the gravity waves look like will give us some clue as to what we are missing.

The other thing to note is that they are leaving out magnetic fields. This is because it's going to take you about three years or so to get 2/3-d hydro working. Putting in a magnetic field model is going to take you another three to five years.

You put in magnetic fields later, because you can get a rotational model that doesn't have magnetic fields, but since the magnetic fields are generated by rotation, it doesn't make any much sense to model magnetic fields without rotation.

Chronos

Its more a matter of massive shock waves that interact in ways we do not understand, and probably have random components. I doubt there is any simple predictive model that would explain every such event.

Aryden

Hello all, I'm new here and have a question that is most likely so elementary as to deserve no response, but here goes:


Could the cessation of reaction occur in a star before the core reaches sufficient mass to collapse, resulting in an omni directional release of energy forcing mass/neutrinos to move away from the object, yet forcing the iron core into a super dense material resulting in a black hole?

twofish-quant

No problem, it's actually a very good question.

This sort of reverses cause and effect. Once nuclear reactions stop, there is nothing holding the a massive star up, so it collapses. Nuclear reactions produce energy, the energy gets trapped, the trapped energy creates pressure which keeps the star from collapsing. With lighter stars, there is something called degenerate pressure that keeps the star from collapsing even without nuclear reactions. Basically, there is an important principle that you can't have two electrons or neutrons in the same energy state at the same time, and with light stars all of the energy states fill up. It's what keeps you from falling through the floor.

Astronuc

FYI - Gravitational Waves from Gravitational Collapse
http://relativity.livingreviews.org/...es/lrr-2003-2/


pdf - http://relativity.livingreviews.org/...003-2Color.pdf