3 ms·

Yes but the mechanism that makes the disk form from the general cloud is physical collisions, two "particles" that have opposite inclinations compared to the av

Yes but the mechanism that makes the disk form from the general cloud is physical collisions, two "particles" that have opposite inclinations compared to the average hit each other and end up closer to that average plane. But basically nothing can hit a black hole that size so where would it get its momentum from?

whatshisface 7y ago
>But basically nothing can hit a black hole that size Why would that be true? Individual gas molecules manage to disk-ify and turn in to planets, I don't see why a black hole couldn't. This would presumably happen in the early stages of system formation when there was a lot of stuff flying around separately.
- qubex 7y ago
  Obviously, nothing can ‘hit’ a black hole: anything that does just gets absorbed by it as it falls in. However, more broadly speaking, the angular momentum is conserved, so the result would be more or less the same. However, given the enormous, ridiculous difference of relative masses (and therefore angular momentum) in the case of black holes and some gas particles, I think my initial point stands.
  - whatshisface 7y ago
    The black hole would interact with many gas particles, not just one. How many would be reasonable? Well, Jupiter is a gas giant and it had to form somehow. Yes, conservation of momentum is the right way to think about that.
    - qubex 7y ago
      > conservation of momentum is the right way to think about that So you’re saying you’d expect a body that were captured at an arbitrary angle to end up orbiting in the same ecliptic as the planets roughly around the sun’s equator?
      - whatshisface 7y ago
        If the body was there from the start it would obey the same rules as all of the dust that was there from the start.
  - jayd16 7y ago
    >anything that does just gets absorbed by it as it falls in. I don't think this is true. Plenty of (almost everything) things would interact with the black hole's gravitation but not be close enough fall in.
    - qubex 7y ago
      You have an object the mass of a gas giant. Planets by definition sweep their local neighbourhood clear of objects. So the black hole is going to carve out an area that is largely devoid of other bodies, and particularly in the context of a gaseous planetary nebula, it’s going to swallow stuff. This will lead to a roughly spherical void around it, and a gravitational bias towards the centre of mass of the planetary nebula (i.e. radially inwards towards the sun).
      - radford-neal 7y ago
        "Planets by definition sweep their local neighbourhood clear of objects" What makes you think that a black hole orbiting the sun is a "planet" by the definition you're using? More generally, you can't prove things about the physical world just by citing somebody's arbitrary definition of a word.
- bladedtoys 7y ago
  Molecules are much lower density than black-holes. If an object were infinitely small, it would never be hit by physical collisions. If it were infinitely massive it would never be affected by them. I would have thought that any model of a black hole in this scenario essentially approximates one of those conditions.
  - nine_k 7y ago
    A close enough gravitational interaction, even if not a collision, could do sufficient momentum exchange.
  - whatshisface 7y ago
    The black hole in this scenario is neither infinitely massive nor infinitely small... 10 times more massive than Earth and five cm across.
fit2rule 7y ago
>where would it get its momentum from? The Sun itself, surely?
foxyv 6y ago
Do not forget that a collision is just an interaction of two objects through a force. Gravitational slingshot maneuvers are a way to bounce a spacecraft off of a planet using gravity as the force. Kind of like bouncing a ball off a fast moving car and seeing it fly off at high speed. A theoretical black hole in our outer solar system would do something similar to low mass objects such as comets and asteroids as well as interstellar gasses.

whatshisface 7y ago

>But basically nothing can hit a black hole that size Why would that be true? Individual gas molecules manage to disk-ify and turn in to planets, I don't see why a black hole couldn't. This would presumably happen in the early stages of system formation when there was a lot of stuff flying around separately.

qubex 7y ago
Obviously, nothing can ‘hit’ a black hole: anything that does just gets absorbed by it as it falls in. However, more broadly speaking, the angular momentum is conserved, so the result would be more or less the same. However, given the enormous, ridiculous difference of relative masses (and therefore angular momentum) in the case of black holes and some gas particles, I think my initial point stands.
- whatshisface 7y ago
  The black hole would interact with many gas particles, not just one. How many would be reasonable? Well, Jupiter is a gas giant and it had to form somehow. Yes, conservation of momentum is the right way to think about that.
  - qubex 7y ago
    > conservation of momentum is the right way to think about that So you’re saying you’d expect a body that were captured at an arbitrary angle to end up orbiting in the same ecliptic as the planets roughly around the sun’s equator?
    - whatshisface 7y ago
      If the body was there from the start it would obey the same rules as all of the dust that was there from the start.
- jayd16 7y ago
  >anything that does just gets absorbed by it as it falls in. I don't think this is true. Plenty of (almost everything) things would interact with the black hole's gravitation but not be close enough fall in.
  - qubex 7y ago
    You have an object the mass of a gas giant. Planets by definition sweep their local neighbourhood clear of objects. So the black hole is going to carve out an area that is largely devoid of other bodies, and particularly in the context of a gaseous planetary nebula, it’s going to swallow stuff. This will lead to a roughly spherical void around it, and a gravitational bias towards the centre of mass of the planetary nebula (i.e. radially inwards towards the sun).
    - radford-neal 7y ago
      "Planets by definition sweep their local neighbourhood clear of objects" What makes you think that a black hole orbiting the sun is a "planet" by the definition you're using? More generally, you can't prove things about the physical world just by citing somebody's arbitrary definition of a word.
bladedtoys 7y ago
Molecules are much lower density than black-holes. If an object were infinitely small, it would never be hit by physical collisions. If it were infinitely massive it would never be affected by them. I would have thought that any model of a black hole in this scenario essentially approximates one of those conditions.
- nine_k 7y ago
  A close enough gravitational interaction, even if not a collision, could do sufficient momentum exchange.
- whatshisface 7y ago
  The black hole in this scenario is neither infinitely massive nor infinitely small... 10 times more massive than Earth and five cm across.

fit2rule 7y ago

>where would it get its momentum from? The Sun itself, surely?

foxyv 6y ago

Do not forget that a collision is just an interaction of two objects through a force. Gravitational slingshot maneuvers are a way to bounce a spacecraft off of a planet using gravity as the force. Kind of like bouncing a ball off a fast moving car and seeing it fly off at high speed. A theoretical black hole in our outer solar system would do something similar to low mass objects such as comets and asteroids as well as interstellar gasses.