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How come we know what a neutron star is made up of but do not know what's inside black holes? A genuine question...

drevil-v2 7y ago
No information leaks out a black hole. It is opaque to the normal Universe.
perlgeek 7y ago
Nothing comes out of a black hole, so we can't get observations from the inside. (There are nit-picky theoretical ways in which a black hole can evaporate, keyword "Hawking Radiation", but as far as I know that hasn't been observed, because it's too weak and too far away. But even then we learn about its surface/event horizon, not its inside).
- cthalupa 7y ago
  We haven't observed hawking radiation coming off of a black hole, but we have observed it in lab settings. https://iopscience.iop.org/article/10.1088/1367-2630/10/10/103001/pdf https://iopscience.iop.org/article/10.1088/1367-2630/10/10/1...
  - perlgeek 7y ago
    I can't let this comment stand as it is. This is a "numerical observation", so a simulation. And not of a black hole, but of a model of a black hole in one dimension in a Bose-Einstein-Condensate. Nobody has created a black hole in a lab and measured its radiation.
    - cthalupa 7y ago
      I specifically stated we have not seen it coming off of a black hole, but dismissing this as just a simulation is silly and reductionist. To do the same in a counter-argument, if I can accurately model fluid dynamics, I don't have to go drop a log in my bathtub to observe the effects. But sure, if you want, we can discount that specific study and focus on others that use different methods to detect it that aren't "just simulations" https://arxiv.org/abs/1009.4634 https://arxiv.org/abs/1009.4634 https://arxiv.org/abs/1401.6612 https://arxiv.org/abs/1401.6612
krzat 7y ago
We know that current theory predicts singularity, which is most likely incorrect.
- username90 7y ago
  Personally I believe the Universe as we know it is the insides of a black hole, and that the predicted "singularity" is wrong. There is no reason why there would be a singularity there, anyone looking at an object smaller than its Schwarzschild radius will just see a black hole since that equation comes from calculating the curvature outside a homogeneous sphere and not outside a singularity. That way the space expansion in the origin of the universe could just be the black hole forming and quickly eating more mass of its surrounding and thus expanding. Also would explain a lot of things related to lack of anti-matter and such since the part of the outer universe our blackhole ate wouldn't necessarily have an even distribution.
  - cthalupa 7y ago
    >Personally I believe the Universe as we know it is the insides of a black hole, and that the predicted "singularity" is wrong. Well, regardless of whether or not our universe is contained within a black hole, basically no one thinks there is literally a singularity of infinite density inside of black holes. It's just what relativity states (and we already know relativity isn't a complete explanation, especially in regards to some of these incredibly extreme situations) and treating black holes like they contain incredibly massive quantities of mass while basically being a point-particle works for all of our day to day purposes. String theory and loop quantum gravity both explain black holes without needing a singularity, and every astrophysicist that I've spoken to a read comments from discussing this topic has basically said "Yeah, it's not a singularity, we just don't know what it is, and that whole singularity thing is close enough"
DebtDeflation 7y ago
Also, because we understand neutron degeneracy pressure, but don't yet know what (if any) quantum effect would prevent an actual singularity from being reached once the upper limit of a neutron star was breached. There is speculation that quark matter and quark stars may exist but no evidence of it yet.
SiempreViernes 7y ago
That's not quite right, we do know what black holes are made up of: the remains of a star. Well, if they are reasonably small they are made out of the remains of a star, if they are too big they can contain the remains of lots of stars and also gas, dust and maybe bits of planets, but exactly how we get the biggest black holes isn't clear. The issue is rather that we don't know what all that star stuff becomes once it goes into the black hole, though there are theories. The problem is that the defining feature of a black hole, its even horizon, by necessity means there is no way of knowing what theory is correct since nothing happening inside is supposed to matter to us. So before we can make any real progress on the interior of black holes we thus need to figure out exactly in what sense the event horizon leaks information, if it does. In contrast, while we don't really know what happens to matter inside a neutron star, its surface remains visible to us and so we have been able to discard many different theories about what goes inside it. There is still debate about the precise equation of state, which correspond to different internal structure the various models represent and so different ideas of how a neutron star is made up. Honestly, I don't know how much difference there are between the various models, but pretty crazy sounding ideas are still popping up, so there must be at least some space left.
- sidcool 7y ago
  Thanks, this was informative. There are a lot of unknowns about black holes, and perhaps far in the future we will come to know as we fly by one such.
- posterboy 7y ago
  I once figured, could most massive stars have a black hole at the center? With thr crazy time dilations around a BH, I imagine the implosion would capture the escaping image of the prior star. I imagine a microscopic black hole at the core of thessun that immediately evaporates, but immediately looks like an eternity for us
  - SiempreViernes 7y ago
    No, you need something releasing a lot of energy in the middle of a star, otherwise it collapses down on itself and stops being a star, the event horizon doesn't provide any supporting pressure. Also, the process that compresses matter to the point it collapses to a black hole is very destructive; there is no reasonable way to form a black hole in the middle of the star.
deleted 7y ago
[deleted]

No information leaks out a black hole. It is opaque to the normal Universe.

Nothing comes out of a black hole, so we can't get observations from the inside. (There are nit-picky theoretical ways in which a black hole can evaporate, keyword "Hawking Radiation", but as far as I know that hasn't been observed, because it's too weak and too far away. But even then we learn about its surface/event horizon, not its inside).

cthalupa 7y ago
We haven't observed hawking radiation coming off of a black hole, but we have observed it in lab settings. https://iopscience.iop.org/article/10.1088/1367-2630/10/10/103001/pdf https://iopscience.iop.org/article/10.1088/1367-2630/10/10/1...
- perlgeek 7y ago
  I can't let this comment stand as it is. This is a "numerical observation", so a simulation. And not of a black hole, but of a model of a black hole in one dimension in a Bose-Einstein-Condensate. Nobody has created a black hole in a lab and measured its radiation.
  - cthalupa 7y ago
    I specifically stated we have not seen it coming off of a black hole, but dismissing this as just a simulation is silly and reductionist. To do the same in a counter-argument, if I can accurately model fluid dynamics, I don't have to go drop a log in my bathtub to observe the effects. But sure, if you want, we can discount that specific study and focus on others that use different methods to detect it that aren't "just simulations" https://arxiv.org/abs/1009.4634 https://arxiv.org/abs/1009.4634 https://arxiv.org/abs/1401.6612 https://arxiv.org/abs/1401.6612

krzat 7y ago

We know that current theory predicts singularity, which is most likely incorrect.

username90 7y ago
Personally I believe the Universe as we know it is the insides of a black hole, and that the predicted "singularity" is wrong. There is no reason why there would be a singularity there, anyone looking at an object smaller than its Schwarzschild radius will just see a black hole since that equation comes from calculating the curvature outside a homogeneous sphere and not outside a singularity. That way the space expansion in the origin of the universe could just be the black hole forming and quickly eating more mass of its surrounding and thus expanding. Also would explain a lot of things related to lack of anti-matter and such since the part of the outer universe our blackhole ate wouldn't necessarily have an even distribution.
- cthalupa 7y ago
  >Personally I believe the Universe as we know it is the insides of a black hole, and that the predicted "singularity" is wrong. Well, regardless of whether or not our universe is contained within a black hole, basically no one thinks there is literally a singularity of infinite density inside of black holes. It's just what relativity states (and we already know relativity isn't a complete explanation, especially in regards to some of these incredibly extreme situations) and treating black holes like they contain incredibly massive quantities of mass while basically being a point-particle works for all of our day to day purposes. String theory and loop quantum gravity both explain black holes without needing a singularity, and every astrophysicist that I've spoken to a read comments from discussing this topic has basically said "Yeah, it's not a singularity, we just don't know what it is, and that whole singularity thing is close enough"

DebtDeflation 7y ago

Also, because we understand neutron degeneracy pressure, but don't yet know what (if any) quantum effect would prevent an actual singularity from being reached once the upper limit of a neutron star was breached. There is speculation that quark matter and quark stars may exist but no evidence of it yet.

SiempreViernes 7y ago

That's not quite right, we do know what black holes are made up of: the remains of a star. Well, if they are reasonably small they are made out of the remains of a star, if they are too big they can contain the remains of lots of stars and also gas, dust and maybe bits of planets, but exactly how we get the biggest black holes isn't clear. The issue is rather that we don't know what all that star stuff becomes once it goes into the black hole, though there are theories. The problem is that the defining feature of a black hole, its even horizon, by necessity means there is no way of knowing what theory is correct since nothing happening inside is supposed to matter to us. So before we can make any real progress on the interior of black holes we thus need to figure out exactly in what sense the event horizon leaks information, if it does. In contrast, while we don't really know what happens to matter inside a neutron star, its surface remains visible to us and so we have been able to discard many different theories about what goes inside it. There is still debate about the precise equation of state, which correspond to different internal structure the various models represent and so different ideas of how a neutron star is made up. Honestly, I don't know how much difference there are between the various models, but pretty crazy sounding ideas are still popping up, so there must be at least some space left.

sidcool 7y ago
Thanks, this was informative. There are a lot of unknowns about black holes, and perhaps far in the future we will come to know as we fly by one such.
posterboy 7y ago
I once figured, could most massive stars have a black hole at the center? With thr crazy time dilations around a BH, I imagine the implosion would capture the escaping image of the prior star. I imagine a microscopic black hole at the core of thessun that immediately evaporates, but immediately looks like an eternity for us
- SiempreViernes 7y ago
  No, you need something releasing a lot of energy in the middle of a star, otherwise it collapses down on itself and stops being a star, the event horizon doesn't provide any supporting pressure. Also, the process that compresses matter to the point it collapses to a black hole is very destructive; there is no reasonable way to form a black hole in the middle of the star.

deleted 7y ago

[deleted]