What happens when a neutron star collapses into a black hole?

[edearl]

Specifically, what happens to the identical fermions in a neutron star as the neutron star collects additional mass that makes it into a black hole. Fermions cannot occupy the same state according to the Pauli exclusion principle, what happens to them in the black hole?

 

[edearl]

TY to the thread "a neutron star collapses - where's pauli?"

 

[mathman]

Specifically, what happens to the identical fermions in a neutron star as the neutron star collects additional mass that makes it into a black hole. Fermions cannot occupy the same state according to the Pauli exclusion principle, what happens to them in the black hole?

The only answer anyone can give today is: we don't know. To answer that question requires a synthesis of general relativity and quantum theory, which doesn't exist.

 

[Bernie G]

Probably neutron stars don't collapse into black holes. Instead black holes are probably formed when much larger stars collapse. It appears the maximum size for a neutron star is about 1.97 solar mass. It looks like something is limiting the maximum neutron star mass so the neutron star doesn't normally grow big enough to collapse into a black hole. Possibly material gets blown off the neutron star surface in a fusion reaction or maybe the core disintegrates into quarks and radiation, and the radiation leaves the star and the quarks recombine to neutrons. Does anybody have any suggestions as to what might be limiting neutron star mass to 1.97 solar mass?

 

[Drakkith]

I remember reading a paper suggesting that it was something to do with the parent star. I believe something happened when the star was in the right range to form neutron stars around 2-3 solar masses or so that caused them to eject more material in the supernova than they normally would if they were under or over that mass range, which means that it's the supernova process that puts the limit on the mass.

 

[Bernie G]

Yes, what's probable is the goal. There could be some kind of event that causes a neutron star to collapse to a black hole, but is that the way most black holes are formed? There probably is an interesting reason why neutron stars are normally limited to 1.97 solar mass.

 

[Bernie G]

High energy colliders show neutrons disintegrate into quark type matter and radiation. Some sources indicate this generates a resulting pressure of about (rho)(c^2)/3. If a black hole isn't a point singularity the fermions shouldn't have to occupy the same space.

 

[Drakkith]

Yes, what's probable is the goal. There could be some kind of event that causes a neutron star to collapse to a black hole, but is that the way most black holes are formed? There probably is an interesting reason why neutron stars are normally limited to 1.97 solar mass.

There are a couple of ways a black hole can form. They can form directly from the core collapse of a massive star, from accretion of material onto a white dwarf from a companion star, accretion of material onto a neutron star, or from collisions between two massive stellar remnants.

 

[Chronos]

The birthing process for black holes is not well understood. There is a fairly significant mass gap between the most massive neutron stars [~2 solar] and the least massive black holes [~5 solar] and we lack a convenient explanation for this apparent anomaly. Theoretically, there should be a relatively smooth transition from neutron stars to black holes at around 3 solar masses, but, observational support is clearly and conspicuously absent. Most neutron star masses are below the chandresakhar limit for white dwarfs [1.44 solar], which is curious and implies physics at work that have not yet been properly modeled [e.g., quantum gravity].

 

[Bernie G]

" There is a fairly significant mass gap between the most massive neutron stars [~2 solar] and the least massive black holes [~5 solar]"

IF neutron stars are self limiting to 2 solar mass there must be a reason. Doesn't it make more sense that if there is an ejection process at 2 solar mass, that this is generally due to what is happening in the core rather than what is happening at the surface?

 

[Bernie G]

Is there a table giving characteristics for neutron stars above approximately 1.75 solar mass? Ideally it would show things like estimated mass, apparent surface temperature, spin rate, average energy per burst, peak energy per burst, burst rate, length of burst, accretion rate of mass, and other things.

 

[Chronos]

There is a table here of neutron star masses [http://www.stellarcollapse.org/sites/default/files/table.pdf] . As you can see, the number of neutron stars with known masses is not exactly huge. Generally speaking, masses can only be determined from stars that belong to binary systems and we have good reason to believe these do not evolve in the same way as solitary neutron stars. The uncertainties are also rather broad. The reference sources likely have some of the more exotic data you are interested in.

 

[Bernie G]

"Specifically, what happens to the identical fermions in a neutron star" ... if it were to collapse to a black hole?

I see your point now. Even if the neutrons were to disintegrate to say 10% quark matter and 90% radiation, that still presents a problem as the quark matter should have a maximum density. Maybe all or almost all of the matter converts to radiation.

 

[twofish-quant]

Specifically, what happens to the identical fermions in a neutron star as the neutron star collects additional mass that makes it into a black hole. Fermions cannot occupy the same state according to the Pauli exclusion principle, what happens to them in the black hole?

Great question.

What happens is that as the energies increase and the matter starts getting relativistic, the energy levels change so that the matter lose stiffness. As you increase the pressure, the energy levels start getting closer and closer which means that in the limit of extreme gravity, you have a lot more energy levels than particles, and you lose Pauli pressure.

The same thing happens with white dwarves.

One other way of thinking about it. The energy levels in a atom are approximately equal energies from each other. If the particles are moving at low speeds, then there are only a limited number of energy states available before you run out and so you fill up all of the energy levels quickly. Now when things start moving near the speed of light, you have can stick in a huge number of energy levels near the speed of light, which means if the energies are high enough, you'll always end up with more empty energy levels than particles.

 

[twofish-quant]

The only answer anyone can give today is: we don't know. To answer that question requires a synthesis of general relativity and quantum theory, which doesn't exist.

In fact it doesn't. We are still at in the densities and masses of "sort of known physics". One way of thinking about it is to imagine the neutron star as a giant atom. As the gravitational pull increases, the energy levels will get closer and closer and you can squeeze more and more particles in the same energy level. Once you get close to the speed of light, then the number of available energy levels increases by a huge number, and Pauli stops keeping the star from collapsing.

 

[twofish-quant]

Theoretically, there should be a relatively smooth transition from neutron stars to black holes at around 3 solar masses, but, observational support is clearly and conspicuously absent. Most neutron star masses are below the chandresakhar limit for white dwarfs [1.44 solar], which is curious and implies physics at work that have not yet been properly modeled [e.g., quantum gravity].

Nope. It's very unlikely that quantum gravity is involved. The density involved are nuclear densities and nowhere near quantum gravity.

The important physics includes

* neutrino energy transfer
* magnetic fields
* turbulence
* nuclear densities
* nuclear reactions
* convection
* rotation

All of those are curiously much more difficult to model than quantum gravity. It turns out that for the places that "interesting things happen" you don't even need general relativity. Typically what you do is to do one run with general relativity, show that it doesn't make a difference, and then run everything Newtonian.

In fact the fact that there is no room for "quantum gravity" makes this a more interesting problem. The trouble with quantum gravity is that you can make up anything, but you can show through some pretty simple arguments, that we are no where near the densities and pressures at which quantum gravity is important. The densities and pressures involved are nuclear, and we can do those experiments on earth.

The irony is that black holes are easy to model. They are round and they are black. Simple.

 

[Cosmo Novice]

The irony is that black holes are easy to model. They are round and they are black. Simple.

I agree with this, they are easy to model - but is this only applicable from an external perspective?

 

[alexg]

Mass, charge and spin are all that can be known about a BH.

 

[Bernie G]

"Mass, charge and spin are all that can be known about a BH."

I'm not so sure about that. If two or three black holes interact, which could happen at the cores of merging galaxies, there might be sufficient forces to tear apart a black hole, if black holes are not a point singularity. Thusly we could see what's in there.

 

[Bernie G]

And you forgot to mention magnetic field.

 

[Chronos]

Accretion is not a good candidate process for neutron stars to evolve into black holes. They tend to get annoyed when fuel accumulates on their surface which leads to nuclear detonations - e.g., http://www-news.uchicago.edu/releases/00/000321.neutron.shtml

 

[Drakkith]

Accretion is not a good candidate process for neutron stars to evolve into black holes. They tend to get annoyed when fuel accumulates on their surface which leads to nuclear detonations - e.g., http://www-news.uchicago.edu/releases/00/000321.neutron.shtml

Hmmm. I think my earlier post was incorrect then. Accretion onto white dwarfs and neutron stars doesn't lead to a collapse...for white dwarfs it does lead to a supernova, but no black hole.

 

[Chronos]

Mergers with a degenerate matter companion [neutron-neutron or neutron-white dwarf] is a different story, albeit that is probably a rare event.

 

[Bernie G]

"Accretion is not a good candidate process for neutron stars to evolve into black holes. They tend to get annoyed when fuel accumulates on their surface which leads to nuclear detonations"

Yes, accretion is probably not a good candidate process for neutron stars to evolve into black holes. But nuclear detonation at the surface is a simulated working model and not an observation. Doesn't it make more sense that if there is an ejection process above about 2 solar mass, that this is generally due to what is happening in the core rather than what is happening at the surface?

 

[twofish-quant]

Yes, accretion is probably not a good candidate process for neutron stars to evolve into black holes. But nuclear detonation at the surface is a simulated working model and not an observation. Doesn't it make more sense that if there is an ejection process above about 2 solar mass, that this is generally due to what is happening in the core rather than what is happening at the surface?

There are two mechanisms. One is if you have a white dwarf and dump stuff on it. In that situation the core starts burning and the whole star gets blown up and you don't leave anything.

In the case of iron core collapse supernova everything is already burned and burning Si doesn't add much energy. It is important because the way that things burn changes the nuclear abundances so that gives you a clue as to what is going on. In particular we know that not too much of the neutron star gets blown away or else all of the iron isotopes would be wrong.

The stuff that does have a lot of energy involves magnetic fields and neutrino interactions.

Also, I disagree with accretion not being a good model for what happens with iron core supernova. You can try to model the star as a neutron star with the rest of the star falling on top of it.

 

[twofish-quant]

I'm not so sure about that. If two or three black holes interact, which could happen at the cores of merging galaxies, there might be sufficient forces to tear apart a black hole, if black holes are not a point singularity. Thusly we could see what's in there.

Nope. Unless GR is wrong, then what happens when you get black holes interacting is an even bigger black hole. Weird stuff might happen with the stuff around the BH, but the BH itself is pretty simple.

What happens when you simulate a neutron star collapse is that the center quickly collapses to a neutron star and sits there as stuff falls on top of it. The only thing way that the core influences the stuff that is falling is that if you have different nuclear equations of state then you change the pressure of the bottom of the interesting area.

It's also interesting to see what happens when something does turn into a black hole. The way that you simulate general relativity is to include a "time dilation" factor (see Van Riper 1979). When the core starts turning into a black hole, the time dilation factor of the layer that goes into the black hole starts going to zero, and from the point of view of the simulation that "freezes" that layer as it falls into the event horizon. From a computer calculation point of view, this is good since by "freezing" the layer, you don't have to spend CPU cycles calculating what happens.

 

[Bernie G]

Ah, there we go again, general relativity supposedly requires a point singularity. Anyway, the blog initial question was about what happens to the fermions, which I interpreted to mean quark type matter. If neutrons collapse, do fermions collapse?

 

[chill_factor]

when electron degeneracy fails, inverse beta decay is energetically favorable such that protons and electrons can merge to form neutrons.

now, is it so much of a stretch to think that at even higher pressures, neutrons, or quarks, have interactions that are favorable to production of a type of boson that we haven't yet observed? this boson would then have no such degeneracy pressure and the entire star could just collapse to however big this boson was (subatomic scales).

 

[Chronos]

... But nuclear detonation at the surface is a simulated working model and not an observation. ...

This looks like an observation to me http://www.nasa.gov/centers/goddard/news/topstory/2004/0220stardisk.html

 

[twofish-quant]

Ah, there we go again, general relativity supposedly requires a point singularity. Anyway, the blog initial question was about what happens to the fermions, which I interpreted to mean quark type matter. If neutrons collapse, do fermions collapse?

Oh.

As the thing goes toward a singularity, all of the energy levels flatten so that Pauli exclusion doesn't stop the collapse. What happens at the singularity is a big unknown. The neutrons get crushed to quarks, but what the quarks get crushed to is a big unknown.

 

[twofish-quant]

now, is it so much of a stretch to think that at even higher pressures, neutrons, or quarks, have interactions that are favorable to production of a type of boson that we haven't yet observed?

It's possible once you reach GUT densities. On the other hand there are some constraints that tell you what is likely to happen.

This boson would then have no such degeneracy pressure and the entire star could just collapse to however big this boson was (subatomic scales).

The thing about degeneracy pressure is that you can show that degeneracy pressure always disappears if you crank up the gravity enough. So even if the fermions stay fermions, the degeneracy pressure disappears.

 

[Bernie G]

So there is no pressure caused by radiation and relativistic particles, approximately equal to (rho)(c^2)/3 ?

 

[twofish-quant]

So there is no pressure caused by radiation and relativistic particles, approximately equal to (rho)(c^2)/3 ?

No degeneracy pressure. I walk on a floor of wood, I don't fall through the floor. If I create a floor of photons, then I can't walk on it.

The problem with non-degeneracy pressure is that it doesn't generate much force. If I take a gas, and increase the density, the pressure only goes up slightly, which means that you don't have much force to resist gravity. If I take a solid, and increase the density even slightly, the pressure increases by a huge amount. So while photons do exert pressure, it's the dependency between density and pressure that matters, and for non-degenerate matter even if the pressure is high, increasing the density only increases the pressure slightly.

As things go relativistic all particles start behaving more like photons, so once the floor of wood goes relativistic it's like a floor of photons (i.e. you can't walk on it).

On thing about these sorts of arguments is that they are independent of the details. We don't know exactly at what mass neutron stars will collapse, but if special relativity is correct, then at some mass they'll collapse.

Also you can put upper limits. If you assume an unknown particle that increases the number of energy states available, so any unknown particle is going to decrease the critical mass. If you look at the estimated critical mass of neutron stars over time, it's gone down, because as you discover new particle interactions, you make the material softer.

One other note, is one big difference between neutron stars and black holes is that neutron stars have a hard surface whereas black holes don't. What this means is that if you look at a one solar mass object, you see big radiation flashes whereas with eight solar mass objects you don't. The explanation for this is that with neutron stars, sometimes matter will bunch up and hit the surface and when that happens there is a huge radiation burst. With black holes, there is no surface, so no radiation bursts.

 

[chill_factor]

It's possible once you reach GUT densities. On the other hand there are some constraints that tell you what is likely to happen.
The thing about degeneracy pressure is that you can show that degeneracy pressure always disappears if you crank up the gravity enough. So even if the fermions stay fermions, the degeneracy pressure disappears.

the degeneracy pressure doesn't really disappear i think, its just that there's really enough energy to force the fermions into very high energy states close to each other (or inside each other). if it did actually disappear i'd think there'd be many problems with even chemistry that we could observe.

No degeneracy pressure. I walk on a floor of wood, I don't fall through the floor. If I create a floor of photons, then I can't walk on it.

The problem with non-degeneracy pressure is that it doesn't generate much force. If I take a gas, and increase the density, the pressure only goes up slightly, which means that you don't have much force to resist gravity. If I take a solid, and increase the density even slightly, the pressure increases by a huge amount. So while photons do exert pressure, it's the dependency between density and pressure that matters, and for non-degenerate matter even if the pressure is high, increasing the density only increases the pressure slightly.

As things go relativistic all particles start behaving more like photons, so once the floor of wood goes relativistic it's like a floor of photons (i.e. you can't walk on it).

On thing about these sorts of arguments is that they are independent of the details. We don't know exactly at what mass neutron stars will collapse, but if special relativity is correct, then at some mass they'll collapse.

Also you can put upper limits. If you assume an unknown particle that increases the number of energy states available, so any unknown particle is going to decrease the critical mass. If you look at the estimated critical mass of neutron stars over time, it's gone down, because as you discover new particle interactions, you make the material softer.

One other note, is one big difference between neutron stars and black holes is that neutron stars have a hard surface whereas black holes don't. What this means is that if you look at a one solar mass object, you see big radiation flashes whereas with eight solar mass objects you don't. The explanation for this is that with neutron stars, sometimes matter will bunch up and hit the surface and when that happens there is a huge radiation burst. With black holes, there is no surface, so no radiation bursts.

accretion disks, converting angular momentum and gravitational potential energy to radiation?

as things go relativistic, can we think of it as "thermalizing" the degenerate materials such that they attain a more "Boltzman-like" distribution?

 

[twofish-quant]

the degeneracy pressure doesn't really disappear i think, its just that there's really enough energy to force the fermions into very high energy states close to each other (or inside each other).

Nope. What happens is that there are more energy states available, and so the effect of having the limited number of energy states disappears.

if it did actually disappear i'd think there'd be many problems with even chemistry that we could observe.

Great!

If you can have fermions at relativistic states, then degeneracy pressure should disappear. Now figuring out how to set up that sort of experiment in the lab is something I'll leave for other people to do.

as things go relativistic, can we think of it as "thermalizing" the degenerate materials such that they attain a more "Boltzman-like" distribution?

Not quite. What happens is that the energy levels change so that fermi and boltzman distributions converge to something that is different than non-relativistic gases.

http://en.wikipedia.org/wiki/Chandrasekhar_limit