Black Holes: Key to the beginning and end of the universe?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Electro522, Nov 2, 2011.

  1. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    From localised increases in matter/ gravity.
    But, from what I'm reading, you're contending that this can't happen except in the presence of a black hole: ergo ALL suns are built on/ around a BH.
     
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  3. KilljoyKlown Whatever Valued Senior Member

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    I'm saying in an early very hot expanding universe, you are not going to ever get enough gravity together to cause stars to form. I don't believe it would happen even once, let alone hundreds of billions of times all over the universe at about the same time. Do you see my problem?

    The question about early BH's. Do you believe they formed before stars as some scientists believe? To me that's a more absurd than thinking stars could form all over the universe without ready made gravity sources.

    Why is it so hard for people to believe that our local universe (all galaxies with visible stars) is nothing more than a natural part of a much greater cosmic structure?
     
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  5. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    So stars only form because of black holes?

    But black holes before stars is absurd?

    :shrug:

    I've got nothing against it all being part of a "great structure", I'd be surprised if it wasn't.
     
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  7. wellwisher Banned Banned

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    Here is an interesting black hole consideration to think about. If we had a hollow shell of mass, whose inside was a vacuum, the center of gravity of this shell would be a point in empty space. From a distance, the mass and gravity of the shell would be mathematically defined by this point in empty space even though the mass of the shell is in its perimeter.

    Relative to black holes, we can only inferred them from a great distance, just like in the above example of the empty shell, with the mass being able to be defined by a point in the center of gravity; nanoblack hole. Could black holes be the centers of gavity of a perimeter thereby defining a point? For example, galaxies have black holes in their centers of gravity, which we can only see from a distance. How do you tell the difference from a center of gavity and a black hole when can only observe both from great distances?
     
  8. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    1) Black holes (and their formation) were predicted by the mathematics long before we found any. They are not simply "centres of gravity" for a shell.
    2) We detect by holes by their interaction with infalling matter.
     
  9. wellwisher Banned Banned

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    A ball would fall toward the center of gravity of a hollow shell, even though this point has no content. The direction of falling is being defined by a distant perimeter. From light years away, if the shell was semi-transparent, it would appear like a nano-black hole causing the pull. I made that term up for center of gravity special effects. We can make up anything if we are too far away to be proven wrong with real data.

    I remember when they began to explore Mars. This planet was close and studied for centuries. But things were learned that nobody saw or expected even though the theory was infallible; as long as we could not see directly. we are much further from black holes or nano holes than we are Mars.
     
  10. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    So what?

    Yeah, obviously, since you appear to be misusing terms.

    Sure. But don't expect it to be taken seriously.

    Again, so what?
     
  11. wellwisher Banned Banned

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    It too bad you are not smart enough to discuss this but feel the need to divert away to protect what you have memorized. Maybe others have the smarts.
     
  12. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    Yeah, and it's too bad that you aren't smart enough to discuss the actual subject, and have to invent your own terms while employing specious arguments.
    I note that, once again, you go directly to attacks on me rather than attempting to support your "idea" or discuss it.
     
  13. wellwisher Banned Banned

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    That is only because you distract and don't contribute. All I would need to do is create a scenario with center of gravity in space, to get a black hole look alike. I like the galaxy example since nobody can prove black hole or center of gravity with irrefutable evidence.
     
  14. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    Correction, you don't contribute and I point out errors.

    Still no support for your contentions?
     
  15. wellwisher Banned Banned

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    Useless.
     
  16. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    Quite.
    But never mind. If you get an education you won't always be so.

    Still no supp...
    Forget it. I didn't really expect any since that's your modus operandi: post drivel, complain when someone points out that it is drivel, divert to personal attacks and still fail to provide support.
     
  17. AlexG Like nailing Jello to a tree Valued Senior Member

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    No, it wouldn't. The interior of a hollow shell has zero gravity. Everything inside it is in free fall.
     
  18. OnlyMe Valued Senior Member

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    I believe he meant a ball outside the hollow sphere. Though I don't see any real point, in this case he is correct.
     
  19. AlphaNumeric Fully ionized Moderator

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    Newton's shell theorem, so? The centre of mass of an object need not be located within a piece of the object.

    Because for black holes of the size observed in Nature no material can possibly exist which is able to hold itself up from gravitational collapse if it were somehow arranged in the manner you described, ie a hollow shell within its own event horizon.

    I hardly think you're in a position to be throwing stones from your glass house.

    Yes, you can. If the shell is outside the event horizon you can see it. If it's inside then it would collapse under the strain. Even if its outside the material strength would be staggering. To build a Dyson Sphere would require making it out of a material whose strength is stronger than solid quark bondings. And that's just considering it's own weight with a star in the middle, never mind a black hole formed from gravitational collapse.
     
  20. KilljoyKlown Whatever Valued Senior Member

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    You didn't say how thick the shell was. If the shell was say 1000 miles thick of some rocky material or some metallic material. I would say from any point within the shell the center of gravity would be about 500 miles into the shell at any point you are closer to. However if you were outside the shell the center of gravity would be at the center of the sphere.
     
  21. billvon Valued Senior Member

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    Agreed, although there would be no "center of gravity" in terms of a place everything was attracted to. Gravity is equipotential inside a massive sphere (which is why Dyson spheres don't work well.)

    There would, however, be a theoretical center of gravity, a place where the center of the spatially averaged contributions of all nearby matter was.

    Not easily. No known force of physics could support a shell of ultradense matter with a vacuum inside.

    Are you asking "how can you tell a black hole from the center of a regular galaxy?" Via several methods. One is that rotating black holes have axial jets of plasma ejected at relativistic speeds; these are relatively easy to detect. Another way is to observe the accretion disk around the black hole.
     
  22. billvon Valued Senior Member

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    Agreed. But a large enough gas cloud has a very large amount of gravity working on it. Remember, gravity is dependent on total mass - so a lot of mass of even a very light substance (like hydrogen or helium) generates a lot of gravity.

    This goes against our intuition, because we think of hydrogen as something we have trouble keeping in a balloon; how absurd that it could ever become so dense that it attracts _itself!_ Yet the Sun is made up primarily of hydrogen, and is incredibly dense at the center (~100 times denser than water) due solely to its own gravitational attraction. And that attraction is not only sufficient to hold all that hydrogen together, it's enough to hold all that hydrogen together as nuclear fusion tries to blow it apart!

    Yes - and that cloud supplies its own gravity. Tiny imperfections in a close-to-homogenous cloud give rise to small concentrations of mass which grow and grow as they absorb everything near them. Radial asymmetries cause rotation, and pretty soon you have a slightly more dense rotating disk of hydrogen, helium, iron, sodium, oxygen, nitrogen etc etc. And from there, planetary formation begins.
     
  23. OnlyMe Valued Senior Member

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    Vacuum is not the problem. We did that sort of thing with vacuum tubes, in the olden days... Gravity itself becomes an issue. If the shell has enough mass to be gravitationally significant, any variation in the force distribution would result in a colapse.

    Another way is to just map the orbits of stars at the center of a galaxy. I had a link to a map of the star trajectories at the center of the Milky Way. I'll try to look it up... http://www.astro.ucla.edu/~ghezgroup/gc/pictures/orbitsMovie.shtml

    A short animation assembled from I think six years of data shows stars in mostly highly elliptical orbits around something unseen...
     

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