What can we see of a Black Hole?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Frud11, Feb 5, 2008.

  1. Frud11 Banned Banned

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    Energy disperses matter, and any disorder at any moment of this process (of heat flowing, or commuting from part of a system to another), is information about the state of individual partitions, of some "evolving" system.

    Physical entropy measures dispersal, information entropy is a measure of order (or disorder)--physical entropy is NOT disorder, despite what a certain Ludwig Boltzmann said all those years ago.
    Both are a kind of snapshot, or time derivative, of some evolution or change.

    Equilibrium is the idea of relaxation, or "finding" a state of lowest energy--greatest dispersal.
    Information about any equilibrium state is also a measure of disorder, or uncertainty.

    A black hole has this reversed, with an instantaneous view of the number of ways to arrange it as its surface, an area.

    If a BH is sufficiently massive, it drags spacetime around its surface, so looking at one means you are looking around it; or it hides behind the curtain of spacetime that its gravity "folds" around it (but it can't disappear completely).

    P.S. wonder if this thread will go straight behind a curtain, or into a black hole (maybe it's already in one)?
     
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  3. Frud11 Banned Banned

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    So what does it mean that (models of) black holes, supposedly real astronomical objects, have time and distance reversed, in the sense that time will cease to exist, but distance won't, from an external observer's perspective, for any object that passes beyond the event horizon?

    An external observer can only see a 2-d surface (of a sphere). Light from an infalling object will appear to persist at the event horizon, the last information available, as the object continues toward the centre of mass of the black hole. The surface can't be observed (by interacting with photons), supposedly, there's only Hawking radiation.

    So the statement "instantaneous view" in the OP is misleading: there is no "view", but there is a surface.
     
    Last edited: Feb 6, 2008
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  5. kaneda Actual Cynic Registered Senior Member

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    A black hole can be "seen" by the radiations it gives off when swallowing matter. By it's accretion disk and by it's spin. Also if something is behind it and a gravitational pull unexplained by conventional light matter.

    It is of course spinning which we can detect in larger BH's. I would forget the time and Hawking radiation for now until some physical evidence is produced.
     
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  7. Frud11 Banned Banned

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    Right. Two external observers could fire photons at each other as they approached a line that was tangent to the surface of an event horizon, and measure the attenuation, or how many photons survive, and how many don't survive an encounter with it, for example. That looks like a way of using light to interact with a black hole. Also the warping of spacetime is "obvious", and would be proportional to the mass (possibly any rotation and frame-dragging).
     
  8. Jozen-Bo The Wheel Spinning King!!! Registered Senior Member

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    Welcome Back Kaneda!!!

    One of the funniest things about black holes is that the bigger they are, the smaller they are. That is, the more massive they are, the smaller they become, and the larger their warping sphere of influence becomes. They also spinning faster as they crush in on themselves. Fascinating stuff.

    When I consider the amount of electromagnetic energy crushed into a spheric black hole, and how electromagnetic energy is the basis of information in the form of the wave/particle, I am forced to wonder how much activity is going on within the hole that we have no awareness about.
     
  9. kaneda Actual Cynic Registered Senior Member

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    Jozen-Bo. I am on a 3 month holiday in Asia and have not been on the internet much lately.

    I think that the cores of black holes would be made of electrons, quarks and such. A neutron star which has an escape velocity of 2/3 light speed still has whole neutrons so more mass which produces a 50% increase in escape velocity need not crush everything out of existence. We know that BH's spin so they cannot have a point source inside them (since a 1D object has no dimensions to show a spin).

    What I found strange was that a stable orbit was found only 100 miles from a black hole of several solar masses. This would be near the centre of a star of that mass, well over a million miles in diameter. You would think it would just suck anything that close in? Maybe gravity behave differently with a black hole than it would from a star?
     
  10. Reiku Banned Banned

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    Yes... welcome back!
     
  11. Reiku Banned Banned

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    We might be able to detect one via a jet-stream. It's a natural occurance of certain black holes which spit out at both ends a stream of energy.
     
  12. draqon Banned Banned

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    perhaps it is made of strings to the core...

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