7 ms·

Maybe there's a zone between neutron stars and black holes where the object consists at least partly of quark-gluon plasma because the neutrons have been forced

by not2b 6y ago

Maybe there's a zone between neutron stars and black holes where the object consists at least partly of quark-gluon plasma because the neutrons have been forced together until they break, but it's a hair too small to form a black hole.

ajross 6y ago
My understanding is that that's been ruled out by fairly routine QCD work. Dark-energy stars are the exotic material du jour in this space.
pdonis 6y ago
There is no such thing as "too small to form a black hole". There is no minimum mass for a black hole. There is a maximum mass for white dwarfs and neutron stars; for white dwarfs, it's about 1.4 solar masses, and for neutron stars, it's somewhere between about 1.5 and 3 solar masses. We can't pin it down for neutron stars any closer because we have a poor understanding of the equation of state of matter in the relevant density and pressure regime. I don't know if quark-gluon plasma is even stable in the relevant density and pressure regime, but if it is, I suppose there could be a maximum mass for a quark-gluon plasma "star" that was somewhat larger than the maximum mass for a neutron star, so there would be a range of masses where gravitational collapse could stop at a quark-gluon plasma star instead of a neutron star, and would not go on to form a black hole.
- perl4ever 6y ago
  >There is no such thing as "too small to form a black hole". >There is no minimum mass for a black hole. The first sentence could be true, but it's not implied by the second sentence being true.
  - pdonis 6y ago
    Hm, yes, I should probably clarify what I meant: what determines whether an object undergoing gravitational collapse forms a black hole is not whether or not it is too small to form a black hole, but whether or not it is too large to form anything else. There is no minimum mass for a black hole, but every stable state of matter we know of short of a black hole has a maximum mass. (And there are good theoretical reasons to suspect that every stable state of matter short of a black hole must have a maximum mass, even if we haven't yet discovered all of the possible ones.) So a collapsing object that is under the maximum mass limit for some stable state other than a black hole (white dwarf, neutron star, etc.) could be said to be "too small to form a black hole" in one sense (since it won't end up collapsing to a black hole), but I think it's more useful to view things in terms of it not being too large to form a stable state short of a black hole.
    - deepspace 6y ago
      I am pretty sure that is what the parent commenter to your first reply meant, at least that is how I understood their question. Semantics aside, I would like to know if one of the possible states you mention might be "more dense than a neutron star but not dense enough to collapse into a black hole"? I.e. some kind of quark-gluon plasma or other exotic state?
      - pdonis 6y ago
        > I would like to know if one of the possible states you mention might be "more dense than a neutron star but not dense enough to collapse into a black hole"? I.e. some kind of quark-gluon plasma or other exotic state? I'm not aware of any such state that is known, and ajross commented upthread (a sibling to my original comment) that he thinks a quark-gluon plasma state has been ruled out by QCD work. I have seen some papers about the "dark energy stars" he mentions in the same comment, but I don't know of any proposed observational test for such objects and they seem highly speculative to me. Note, btw, that there isn't an awful lot of room for objects more dense than a neutron star but which can remain stable against collapse to a black hole. There is a theorem called Buchdahl's Theorem that says that any stable object that doesn't collapse to a black hole must have a radius at least 9/8 of the Schwarzschild radius corresponding to its mass. The denser neutron stars are already fairly close to this limit.
        perl4ever 6y ago
        There's something on Wikipedia about how maybe all black holes are basically a ball of subatomic stuff, termed a "fuzzball", with a diameter equal to where escape velocity reaches c. This appeals to me, because falling past an event horizon, let alone reaching a singularity, seems like it can't be physical. https://en.wikipedia.org/wiki/Fuzzball_(string_theory) https://en.wikipedia.org/wiki/Fuzzball_(string_theory)
        pdonis 6y ago
        > "fuzzball" As the article notes, this is a speculation in string theory. Since it has no testable consequences, it remains a speculation. > falling past an event horizon, let alone reaching a singularity, seems like it can't be physical "Seems like" is not a good indicator in relativity; lots of things in relativity are counterintuitive. This is one of them. The classical GR model of black holes is perfectly consistent. It's possible that there are quantum corrections that prevent that exact model from being realized in our actual universe, but until we have a good theory of quantum gravity that has actually passed some experimental tests, the classical GR model of black holes is the best we have.
- _joe 6y ago
  The hard upper limit on a neutron star mass, the Rhoades-Ruffini limit, is at 3.2 solar masses. This discovery is significant, because we never found a collapsed object in the 2-3 solar masses range, but it definitely doesn't need new physics to be explained.
- philipov 6y ago
  There is in fact a minimum mass for a black hole. That's called the Plank Mass, which is the amount of mass that forms a Black Hole with a size of 1 plank length. This is also the maximum mass of an elementary point particle.
  - mhh__ 6y ago
    If you can show that there's probably a nobel prize waiting for you
  - pdonis 6y ago
    > There is in fact a minimum mass for a black hole. That's called the Plank Mass This is a speculative hypothesis at this point, since we do not have a good theory of quantum gravity. A lot of physicists think it will turn out to be true once we do have a good theory of quantum gravity, but it's still a speculative hypothesis at this point. > This is also the maximum mass of an elementary point particle. This is part of the same speculative hypothesis.
  - wnoise 6y ago
    There is no reason beyond numerology to believe that any of the Planck units actually mean anything.
    - dogma1138 6y ago
      Plank Units represent physical constants, they are there to make equations and more importantly hypotheses/predictions continue to work in a world where measurements can be constantly refined. Hence they their actual SI values have quite a bit over the years. This is also why Plank units aren’t used much outside of theoretical physics and cosmology which are fields where using absolute value based on current measurements won’t mean that much.
  - Dylan16807 6y ago
    Yeah, okay, but we're talking about stellar objects. In that context, there is no minimum mass for a black hole. If you can figure out a way to cram the mass together. But that was the point of the first comment anyway, that if you didn't quite get enough mass+density that you might get something weird.
- BurningFrog 6y ago
  > for white dwarfs, it's about 1.4 solar masses, and for neutron stars, it's somewhere between about 1.5 and 3 solar masses. A simple thought is that a 2.6 solar mass object could form by two ~1.3 solar mass objects merging.
joe_the_user 6y ago
Like a Quark Star, say? The wikipedia article mentions a number of hypothetical exotic star types. https://en.wikipedia.org/wiki/Quark_star https://en.wikipedia.org/wiki/Quark_star

by not2b 6y ago

ajross 6y ago

My understanding is that that's been ruled out by fairly routine QCD work. Dark-energy stars are the exotic material du jour in this space.

pdonis 6y ago

There is no such thing as "too small to form a black hole". There is no minimum mass for a black hole. There is a maximum mass for white dwarfs and neutron stars; for white dwarfs, it's about 1.4 solar masses, and for neutron stars, it's somewhere between about 1.5 and 3 solar masses. We can't pin it down for neutron stars any closer because we have a poor understanding of the equation of state of matter in the relevant density and pressure regime. I don't know if quark-gluon plasma is even stable in the relevant density and pressure regime, but if it is, I suppose there could be a maximum mass for a quark-gluon plasma "star" that was somewhat larger than the maximum mass for a neutron star, so there would be a range of masses where gravitational collapse could stop at a quark-gluon plasma star instead of a neutron star, and would not go on to form a black hole.

perl4ever 6y ago
>There is no such thing as "too small to form a black hole". >There is no minimum mass for a black hole. The first sentence could be true, but it's not implied by the second sentence being true.
- pdonis 6y ago
  Hm, yes, I should probably clarify what I meant: what determines whether an object undergoing gravitational collapse forms a black hole is not whether or not it is too small to form a black hole, but whether or not it is too large to form anything else. There is no minimum mass for a black hole, but every stable state of matter we know of short of a black hole has a maximum mass. (And there are good theoretical reasons to suspect that every stable state of matter short of a black hole must have a maximum mass, even if we haven't yet discovered all of the possible ones.) So a collapsing object that is under the maximum mass limit for some stable state other than a black hole (white dwarf, neutron star, etc.) could be said to be "too small to form a black hole" in one sense (since it won't end up collapsing to a black hole), but I think it's more useful to view things in terms of it not being too large to form a stable state short of a black hole.
  - deepspace 6y ago
    I am pretty sure that is what the parent commenter to your first reply meant, at least that is how I understood their question. Semantics aside, I would like to know if one of the possible states you mention might be "more dense than a neutron star but not dense enough to collapse into a black hole"? I.e. some kind of quark-gluon plasma or other exotic state?
    - pdonis 6y ago
      > I would like to know if one of the possible states you mention might be "more dense than a neutron star but not dense enough to collapse into a black hole"? I.e. some kind of quark-gluon plasma or other exotic state? I'm not aware of any such state that is known, and ajross commented upthread (a sibling to my original comment) that he thinks a quark-gluon plasma state has been ruled out by QCD work. I have seen some papers about the "dark energy stars" he mentions in the same comment, but I don't know of any proposed observational test for such objects and they seem highly speculative to me. Note, btw, that there isn't an awful lot of room for objects more dense than a neutron star but which can remain stable against collapse to a black hole. There is a theorem called Buchdahl's Theorem that says that any stable object that doesn't collapse to a black hole must have a radius at least 9/8 of the Schwarzschild radius corresponding to its mass. The denser neutron stars are already fairly close to this limit.
      - perl4ever 6y ago
        There's something on Wikipedia about how maybe all black holes are basically a ball of subatomic stuff, termed a "fuzzball", with a diameter equal to where escape velocity reaches c. This appeals to me, because falling past an event horizon, let alone reaching a singularity, seems like it can't be physical. https://en.wikipedia.org/wiki/Fuzzball_(string_theory) https://en.wikipedia.org/wiki/Fuzzball_(string_theory)
        pdonis 6y ago
        > "fuzzball" As the article notes, this is a speculation in string theory. Since it has no testable consequences, it remains a speculation. > falling past an event horizon, let alone reaching a singularity, seems like it can't be physical "Seems like" is not a good indicator in relativity; lots of things in relativity are counterintuitive. This is one of them. The classical GR model of black holes is perfectly consistent. It's possible that there are quantum corrections that prevent that exact model from being realized in our actual universe, but until we have a good theory of quantum gravity that has actually passed some experimental tests, the classical GR model of black holes is the best we have.
_joe 6y ago
The hard upper limit on a neutron star mass, the Rhoades-Ruffini limit, is at 3.2 solar masses. This discovery is significant, because we never found a collapsed object in the 2-3 solar masses range, but it definitely doesn't need new physics to be explained.
philipov 6y ago
There is in fact a minimum mass for a black hole. That's called the Plank Mass, which is the amount of mass that forms a Black Hole with a size of 1 plank length. This is also the maximum mass of an elementary point particle.
- mhh__ 6y ago
  If you can show that there's probably a nobel prize waiting for you
- pdonis 6y ago
  > There is in fact a minimum mass for a black hole. That's called the Plank Mass This is a speculative hypothesis at this point, since we do not have a good theory of quantum gravity. A lot of physicists think it will turn out to be true once we do have a good theory of quantum gravity, but it's still a speculative hypothesis at this point. > This is also the maximum mass of an elementary point particle. This is part of the same speculative hypothesis.
- wnoise 6y ago
  There is no reason beyond numerology to believe that any of the Planck units actually mean anything.
  - dogma1138 6y ago
    Plank Units represent physical constants, they are there to make equations and more importantly hypotheses/predictions continue to work in a world where measurements can be constantly refined. Hence they their actual SI values have quite a bit over the years. This is also why Plank units aren’t used much outside of theoretical physics and cosmology which are fields where using absolute value based on current measurements won’t mean that much.
- Dylan16807 6y ago
  Yeah, okay, but we're talking about stellar objects. In that context, there is no minimum mass for a black hole. If you can figure out a way to cram the mass together. But that was the point of the first comment anyway, that if you didn't quite get enough mass+density that you might get something weird.
BurningFrog 6y ago
> for white dwarfs, it's about 1.4 solar masses, and for neutron stars, it's somewhere between about 1.5 and 3 solar masses. A simple thought is that a 2.6 solar mass object could form by two ~1.3 solar mass objects merging.

joe_the_user 6y ago

Like a Quark Star, say? The wikipedia article mentions a number of hypothetical exotic star types. https://en.wikipedia.org/wiki/Quark_star https://en.wikipedia.org/wiki/Quark_star