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How do you know the object is compact? The idea is that quark degeneracy pressure is enough to keep the object from ever becoming dense enough to form a black h

by ars 4y ago

How do you know the object is compact? The idea is that quark degeneracy pressure is enough to keep the object from ever becoming dense enough to form a black hole. No one knows the actual quark degeneracy pressure, so no one knows if stars collapse to black holes or if they get stopped.

pdonis 4y ago
> How do you know the object is compact? Because we have these objects with huge masses but we can't see them, and such objects have to be compact. Objects with those masses that do not emit huge amounts of light that make them easily visible (i.e., that are not stars) can't not be compact. They either have to be held up by degeneracy pressure, which means they are either white dwarfs or neutron stars/quark stars, or they have undergone complete gravitational collapse and are black holes. All of those objects are compact, and there are no other possibilities. > No one knows the actual quark degeneracy pressure, so no one knows if stars collapse to black holes or if they get stopped. This is not correct. I have already explained why: the maximum mass limit. That limit applies regardless of what the actual quark degeneracy pressure turns out to be in an actual gravitational collapse. It is a fundamental fact about relativistic degeneracy.
- ars 4y ago
  We were using different definitions of compact. I assumed you meant compact enough to form a black hole. You have not explained sufficiently about the maximum mass limit, there are plenty of suns that are enormously massive, but they're not black holes because heat is keeping the density from increasing. The same thing would happen with a quark star or a strange star, the degeneracy pressure would keep it from ever becoming a black hole, at least until the pressure was overcome but we don't know what that pressure is. What I'm saying is we cannot distinguish between a black hole and a quark star, not with our present observations.
  - pdonis 4y ago
    > You have not explained sufficiently about the maximum mass limit Yes, I have: I said it applies to objects supported by degeneracy pressure. Ordinary stars are not; as you note, they are supported by thermal pressure. But thermal pressure never lasts forever; eventually any star will stop being able to produce heat and will collapse until it is either supported by degeneracy pressure, or forms a black hole. The maximum mass limit is a limit on the first alternative. Also, as I said, an object supported by thermal pressure will be easily visible since it will emit lots of radiation. The objects that we believe are black holes are not doing that, so they can't be supported by thermal pressure anyway. > The same thing would happen with a quark star or a strange star, the degeneracy pressure would keep it from ever becoming a black hole Not if it is over the maximum mass limit. Sorry, but you are simply wrong as regards what the actual physics says. For the gory details, look up the Harrison-Wakano-Wheeler equation of state, or consult the classic textbook by Shapiro and Teukolsky. > at least until the pressure was overcome but we don't know what that pressure is. The whole point of the maximum mass limit is that any pressure, no matter how large, will be overcome if an object is over the limit. That's why we don't need to know what the actual pressure is. > What I'm saying is we cannot distinguish between a black hole and a quark star, not with our present observations. And what you are saying is wrong. See above.

by ars 4y ago

pdonis 4y ago

> How do you know the object is compact? Because we have these objects with huge masses but we can't see them, and such objects have to be compact. Objects with those masses that do not emit huge amounts of light that make them easily visible (i.e., that are not stars) can't not be compact. They either have to be held up by degeneracy pressure, which means they are either white dwarfs or neutron stars/quark stars, or they have undergone complete gravitational collapse and are black holes. All of those objects are compact, and there are no other possibilities. > No one knows the actual quark degeneracy pressure, so no one knows if stars collapse to black holes or if they get stopped. This is not correct. I have already explained why: the maximum mass limit. That limit applies regardless of what the actual quark degeneracy pressure turns out to be in an actual gravitational collapse. It is a fundamental fact about relativistic degeneracy.

ars 4y ago
We were using different definitions of compact. I assumed you meant compact enough to form a black hole. You have not explained sufficiently about the maximum mass limit, there are plenty of suns that are enormously massive, but they're not black holes because heat is keeping the density from increasing. The same thing would happen with a quark star or a strange star, the degeneracy pressure would keep it from ever becoming a black hole, at least until the pressure was overcome but we don't know what that pressure is. What I'm saying is we cannot distinguish between a black hole and a quark star, not with our present observations.
- pdonis 4y ago
  > You have not explained sufficiently about the maximum mass limit Yes, I have: I said it applies to objects supported by degeneracy pressure. Ordinary stars are not; as you note, they are supported by thermal pressure. But thermal pressure never lasts forever; eventually any star will stop being able to produce heat and will collapse until it is either supported by degeneracy pressure, or forms a black hole. The maximum mass limit is a limit on the first alternative. Also, as I said, an object supported by thermal pressure will be easily visible since it will emit lots of radiation. The objects that we believe are black holes are not doing that, so they can't be supported by thermal pressure anyway. > The same thing would happen with a quark star or a strange star, the degeneracy pressure would keep it from ever becoming a black hole Not if it is over the maximum mass limit. Sorry, but you are simply wrong as regards what the actual physics says. For the gory details, look up the Harrison-Wakano-Wheeler equation of state, or consult the classic textbook by Shapiro and Teukolsky. > at least until the pressure was overcome but we don't know what that pressure is. The whole point of the maximum mass limit is that any pressure, no matter how large, will be overcome if an object is over the limit. That's why we don't need to know what the actual pressure is. > What I'm saying is we cannot distinguish between a black hole and a quark star, not with our present observations. And what you are saying is wrong. See above.