Nuetron star collapses to B.H., a final plunge of matter and energy?

[Spinnor]

The moment before a neutron star collapses matter is distributed across the whole volume of the neutron star?

Can we say anything of the actual collapse, such as matter moves towards the center of the neutron star?

 

[mathman]

The moment before a neutron star collapses matter is distributed across the whole volume of the neutron star?

Can we say anything of the actual collapse, such as matter moves towards the center of the neutron star?

Not really. What goes on inside a black hole is an open question of physics theory. Quantum theory and general relativity are in conflict here.

 

[yuiop]

Not really. What goes on inside a black hole is an open question of physics theory. Quantum theory and general relativity are in conflict here.

Spinnor was not asking what happens inside a black hole. He was asking what happens just before a black hole forms, as a neutron star collapses from say 9/8Rs towards r= Rs.

 

[mathman]

I am no expert on the specifics here, but I know in the case of white dwarfs you end up with a Supernova Ia explosion. I suspect something similar will happen for neutron stars.

 

[pervect]

I'm not quite sure what the OP was asking, or why...

 

[Spinnor]

Spinnor was not asking what happens inside a black hole. He was asking what happens just before a black hole forms, as a neutron star collapses from say 9/8Rs towards r= Rs.

I did want to know what happens after collapse. I do have this picture of matter no longer being able to resist the collapse, after adding enough matter to a neutron star, and the matter "actually" moving towards the center. Is this correct, I don't know if General Relativity allows us to calculate what goes on during collapse.

Thanks for the help!

 

[Spinnor]

I'm not quite sure what the OP was asking, or why...

I thought my title said it all,

Neutron star collapses to B.H., a final plunge of matter and energy?

Thanks.

 

[Spinnor]

I thought my title said it all,

Neutron star collapses to B.H., a final plunge of matter and energy?

Thanks.

From Gravitation, page 863, realistic gravitational collapse-an overview:

"... within a fraction of a second the instability develops into a full scale implosion: for realistic density distributions, the stellar core falls rapidly inward on itself, and the outer envelopes trail along behind. ..."

But as pointed out

"... What goes on inside a black hole is an open question of physics theory. Quantum theory and general relativity are in conflict here. "

 

[yuiop]

But as pointed out

"... What goes on inside a black hole is an open question of physics theory. Quantum theory and general relativity are in conflict here. "

I was just making the point that if we can not discuss what goes on inside a black hole, that we can still talk about what happens in the stages immediately prior to the formation of the black hole.

I believe GR can tell us a lot about what happens at this stage, but the calculations are non trivial, because the simplest Schwarzschild solutions assume a static spacetime which is not the case during during a collapse.

 

[twofish-quant]

Can we say anything of the actual collapse, such as matter moves towards the center of the neutron star?

Yes. It's not that hard to model the collapse of a neutron star to a black hole. It's really not that hard to model an implosion for a core collapse supernova. It's the explosion that causes problems.

The way that you model a collapsing neutron star is with a scheme by Van Riper (1979). What happens is that each layer of the star has a different clock, and as the center stars to form a black hole you slow the clocks down, so the computer doesn't actually calculate what happens after the neutron star becomes a black hole, but just slows the clocks down as you get closer and closer to turning into a black hole.

It turns out that this doesn't change what happens to the supernova explosion since the stuff that determines whether there is an explosion or not happens far enough away from the center that you don't have to worry about GR.

 

[twofish-quant]

I believe GR can tell us a lot about what happens at this stage, but the calculations are non trivial, because the simplest Schwarzschild solutions assume a static spacetime which is not the case during during a collapse.

If you run a computer simulation, they really aren't that hard. Van Riper (1979) published a scheme that you can add GR to any spherical calculation.

http://adsabs.harvard.edu/abs/1979ApJ...232..558V

The hard / unknown part isn't really the general relativity. That's easy to calculate. The hard / messy / unknown part is how neutron star material behaves under high density. The question (which is really unknown) is whether neutron star matter is "soft" or "stiff." It it turns out to be soft, then things will quickly collapse to a black hole if you pile on enough matter. If it's "stiff" then the collapse is going to be slower.

 

[yuiop]

I'm not quite sure what the OP was asking, or why...

His question followed on from a previous thread he started here https://www.physicsforums.com/showthread.php?t=352429 and I assumed the two questions are connected. In that other thread I mentioned that that proper time appears to stop or even go backwards when analysed using the Schwarzschild interior solution, but that was a very simplistic analysis assuming even mass density distribution and a static situation which is almost certainly not the case in reality. A step closer to a more realistic answer would require a better knowledge of the real mass distribution of the neutron star immediately prior to the collapse and a knowledge of how the particles move during the collapse and how that affects the mass density distribution during the collapse. I assumed that was where his second question was leading. I am sure there are many other factors such as degeneracy pressure and stress that have to be taken into account also.

 

[twofish-quant]

but that was a very simplistic analysis assuming even mass density distribution and a static situation which is almost certainly not the case in reality.

I think the big question is whether or not the situation as described is physically possible or if someone is putting in an unphysical assumption.

A step closer to a more realistic answer would require a better knowledge of the real mass distribution of the neutron star immediately prior to the collapse and a knowledge of how the particles move during the collapse and how that affects the mass density distribution during the collapse.

If anyone is interested in a Ph.D. dissertation project, I have a slightly used supernova hydro code that could be used to study this question. What's interesting here is that most supernova code really doesn't care very much about the center of the star, and most calculations are made assuming Newtonian gravity since it is less computationally intensive.

To get the code to calculate this, you'd have to do some GR work, since I think the Van Riper formalism would break down in this situation. What I'd do is to forget about using real equations of state, and run the simulation with some polytropic equation of state.

I assumed that was where his second question was leading. I am sure there are many other factors such as degeneracy pressure and stress that have to be taken into account also.

Those are in the EOS, but they shouldn't matter.