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

1. ### edearl

18
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?

2. ### edearl

18
TY to the thread "a neutron star collapses - where's pauli?"

3. ### mathman

6,437
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.

4. ### Bernie G

136
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?

### Staff: Mentor

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.

6. ### Bernie G

136
Yes, whats 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.

7. ### Bernie G

136
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.

### Staff: Mentor

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.

9. ### Chronos

9,881
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].

Last edited: Mar 5, 2012
10. ### Bernie G

136
" 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?

11. ### Bernie G

136
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.

12. ### Chronos

9,881
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.

13. ### Bernie G

136
"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.

14. ### twofish-quant

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.

Last edited: Mar 6, 2012
15. ### twofish-quant

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.

16. ### twofish-quant

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.

Last edited: Mar 6, 2012
17. ### Cosmo Novice

366
I agree with this, they are easy to model - but is this only applicable from an external perspective?

18. ### alexg

126
Mass, charge and spin are all that can be known about a BH.

19. ### Bernie G

136
"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 whats in there.

20. ### Bernie G

136
And you forgot to mention magnetic field.
{"extraction_info": {"found_math": false, "script_math_tex": 0, "script_math_asciimath": 0, "math_annotations": 0, "math_alttext": 0, "mathml": 0, "mathjax_tag": 0, "mathjax_inline_tex": 0, "mathjax_display_tex": 0, "mathjax_asciimath": 0, "img_math": 0, "codecogs_latex": 0, "wp_latex": 0, "mimetex.cgi": 0, "/images/math/codecogs": 0, "mathtex.cgi": 0, "katex": 0, "math-container": 0, "wp-katex-eq": 0, "align": 0, "equation": 0, "x-ck12": 0, "texerror": 0, "math_score": 0.8251184225082397, "perplexity": 644.2034110942151}, "config": {"markdown_headings": true, "markdown_code": true, "boilerplate_config": {"ratio_threshold": 0.18, "absolute_threshold": 10, "end_threshold": 15, "enable": true}, "remove_buttons": true, "remove_image_figures": true, "remove_link_clusters": true, "table_config": {"min_rows": 2, "min_cols": 3, "format": "plain"}, "remove_chinese": true, "remove_edit_buttons": true, "extract_latex": true}, "warc_path": "s3://commoncrawl/crawl-data/CC-MAIN-2015-14/segments/1427131309986.40/warc/CC-MAIN-20150323172149-00086-ip-10-168-14-71.ec2.internal.warc.gz"}