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Why is it so accepted that matter falls into black holes?

  1. Aug 19, 2011 #1
    It seems like black holes could just as easily be expelling the matter they rip up. Couldn't a black hole just be something that rips matter apart atom by atom and then blasts it back into space? In this case there wouldn't be a need for a singularity. Quasars are one example of how they expel matter/energy. Maybe nothing goes beyond the event horizon and instead just gets churned up and around and blasted back out.
     
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  3. Aug 19, 2011 #2

    mathman

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    Black holes are simply highly dense masses, defined by having a gravitational strength so great that the escape velocity is greater than the speed of light.

    What goes on inside is an open question. The singularity is predicted by General Relativity, but quantum theory is not taken into account. When calculations are made using both theories, nonsense results.
     
  4. Aug 19, 2011 #3
    If the escape velocity is greater than the speed of light then how does the material from quasars escape? I know they say that a black hole takes in too much matter than it can handle and expels it but how does that light escape?
     
  5. Aug 19, 2011 #4

    PAllen

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    The light comes from matter well outside the event horizon. Black holes can tear apart approaching stars well before their matter settles near the horizon, leading to very strong radiation emission and jets.
     
  6. Aug 20, 2011 #5
    Who says that?

    Nobody says that.
     
  7. Aug 20, 2011 #6

    Ryan_m_b

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    Once something has gone beyond the event horizon it cannot come out because to do so would require a velocity faster than light. In addition tidal forces around a black hole cause http://en.wikipedia.org/wiki/Spaghettification" [Broken].

    By "expelled matter" you may be confusing the jets seen in http://en.wikipedia.org/wiki/Accretion_disc" [Broken].
     
    Last edited by a moderator: May 5, 2017
  8. Aug 20, 2011 #7

    Drakkith

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    Astroboy, a black hole acts EXACTLY like anything else with mass until you reach the event horizon. Other than strength and gradiant, the Earths gravitational field has the same effect on matter that a black hole does. One can orbit a black hole, use it for slingshot maneuvers, laugh at it's face for being supermassively fat (Bad black hole! *swats with newspaper* I told you TWO stars per million years! Two!), etc.
     
  9. Aug 20, 2011 #8
    Is anything known about the nature of things beyond the event horizon? Specifically how light is not fast enough to escape (once it goes beyond the event horizon), does this mean matter is falling into a black hole faster than light? If so, is this an exception to the cosmic speed limit?
     
  10. Aug 20, 2011 #9

    Drakkith

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    In-falling matter does not exceed the speed of light. As to the why light cannot escape, I believe it has to do with the curvature of space inside the event horizon making it so that all paths available to a photon lead back to the black hole.
     
  11. Aug 21, 2011 #10
    I also think you are confusing the rad streams at the poles vs the eccretion disc. The disc or quasar is everything falling in or in the orbit.

    To add on to this thread's question, how does the radiation at the poles escape if it starts below the EH? How is it launched out, + and - charged particles?
     
  12. Aug 21, 2011 #11

    PAllen

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    Nothing escapes from the event horizon (classically). Hawking radiation from astronomic black holes is much more dim than cosmic background radiation. Polar emissions from a rotating black holes system originate above the event horizon, strong EM fields playing the major role.

    From the point of view of external observers (us) nothing ever reaches the event horizon, so it is not even conceivable to talk about escape from below the event horizon for an external observer.
     
  13. Aug 22, 2011 #12
    This is not neccesarily true - Hawking predicts that Black Holes lose mass via the process of Hawking radiation. The smaller the BH the more ,mass it radiates.

    I do however concede that when "something" goes in it can only come out as "something else" - ie: there is no preservation of state.
     
    Last edited by a moderator: May 5, 2017
  14. Aug 22, 2011 #13

    Ryan_m_b

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    To be fair Hawking radiation is not something escaping from beyond the event horizon. As I understand it (and my knowledge is based on pop-sci books I read years ago so I could be wrong) Hawking radiation works by the black hole making virtual particles-pairs real right on the cusp of the event horizon, it absorbs one of the pair that has negative energy (thus lowering the holes mass) causing the radiation of the positive energy particle.
     
  15. Aug 22, 2011 #14
    Yes I can concede this - the particles are not directly escaping from beyond the EH. I wanted to just outline a mechansim for mass loss. :smile:
     
  16. Aug 22, 2011 #15

    WannabeNewton

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    Classically I don't see how this could be at all. Past the EH (r < 2M for schwarzchild Black holes) you will see that the time - like coordinate and space - like radial coordinate switch signs. Since r becomes time - like past the EH, r = 0 becomes inevitable. We know that a test particle can pass the EH in finite proper time and finite proper distance so why wouldn't it go through and, due to the aforementioned issue, meet the infinite tidal forces at r = 0?
     
  17. Aug 22, 2011 #16
    You're referring to theoretical models? What if the EH is just a buzzsaw that shreds matter and then bats it back out into space? I don't see why it anything has to pass the EH.
     
  18. Aug 23, 2011 #17

    Drakkith

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    We have nothing but theoretical models. Perhaps you do not know what a theoretical model actually means. Do you know what a scientific theory is?
     
  19. Aug 23, 2011 #18
    Can black holes still add to their own mass? If matter falls into a black hole, could it be that this matter is just absorbed and just makes the hole bigger? Or does a black hole have a finite amount of mass it can sustain?
     
  20. Aug 23, 2011 #19

    Ryan_m_b

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    Any mass that crosses the event horizon is added to the black hole. Think of it this way: if matter falls through Earth's atmosphere then it adds to Earth's mass. Simplistically the only difference between this and a black hole is that the escape velocity of a black hole is faster than light speed (thus an event horizon forms) and according to current understanding anything beyond an event horizon is crushed into a singularity of zero volume, infinite density. Though regarding the latter as I understand it the consensus is that our understanding of singularities is incomplete.
     
  21. Aug 25, 2011 #20
    there is nothing inside a black hole. at the event horizon matter is converted to zero point energy and ceases to exist as real mass.
     
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