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Thread: Do black holes grow larger as they pull in more mass?

  1. #1 Do black holes grow larger as they pull in more mass? 
    Forum Freshman zazzerak's Avatar
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    I used to be under the impression that black holes do not gain size, and that all of them are the same size, no bigger than an atom, but their gravitational fields varied.
    and also that any matter coming towards them would Spagettify into a line of molecules and then they would be converted to Hawking radiation. But know I am hearing about theories such as black holes are just concentrated bodies of Dark energy, or that they are some form of worm hole.
    I need a second opinion.


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    The singularity is smaller than a proton. However the black hole, or event horizon, that envelopes the singularity, grows as the mass of the singularity increases.

    P.S. matter crossing the event horizon does not instantly become Hawking Radiation. Supposedly, if a Virtual Particle Pair formed near the event horizon so that one of the virtual particles entered the black hole, the other virtual particle could not pair up and annihilate. It would become a real particle by stealing energy from the black hole. This would be an incredibly slow process, as most black holes accrete more energy from the Cosmic Microwave Background than they would lose to Hawking Radiation.


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    Moderator Moderator Dishmaster's Avatar
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    In addition, the "size" of a Black Hole is often taken as the radius of the event horizon. This radius depends on the total mass of the Black Hole. Therefore, it increases while it gains mass.
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  5. #4 Ah. 
    Forum Freshman zazzerak's Avatar
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    so the black hole itself does not gain size, only the event horizon.
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  6. #5 Re: Ah. 
    Administrator KALSTER's Avatar
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    Quote Originally Posted by zazzerak
    so the black hole itself does not gain size, only the event horizon.
    A black hole is the whole thing, which includes the even horizon and the singularity at the centre. So if the event horizon grows that means the black hole is growing. The more mass that crosses the event horizon, the bigger the event horizon becomes.
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  7. #6  
    Forum Freshman zazzerak's Avatar
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    okay. the singularity doesn't change only the event horizon, and overall size of the black hole.
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    Yes. Some suppose that at the center of the black hole there is not a singularity but a ring. A Kerr ring.

    http://en.wikipedia.org/wiki/Ring_singularity

    But yes the event horizon does grow as matter falls in.
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    I thought black holes destroy matter. How could it possibly get bigger if it acts as an anti matter?
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    Quote Originally Posted by c_a_miller
    I thought black holes destroy matter. How could it possibly get bigger if it acts as an anti matter?
    It doesn't act as antimatter...
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    The singularity is an unproven idea. We do not know if fundamental particles like electrons and quarks (assuming they are as small as "matter" gets), can be crushed. We do know that something as large as a neutron can survive in a neutron star where the escape velocity is upto 2/3 c, so a black hole is not really that much more. It is possible that inside a black hole is a perfect sphere of fundamental particles, spinning. That would explain the rotation of black holes (upto almost light speed for super massive black holes) which a singularity does not.

    Black holes are always measured size wise by their event horizon since that is all we can detect. The largest so far is 18 billion solar masses.
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  12. #11  
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    Quote Originally Posted by Cyberia
    The singularity is an unproven idea. We do not know if fundamental particles like electrons and quarks (assuming they are as small as "matter" gets), can be crushed. We do know that something as large as a neutron can survive in a neutron star where the escape velocity is upto 2/3 c, so a black hole is not really that much more. It is possible that inside a black hole is a perfect sphere of fundamental particles, spinning. That would explain the rotation of black holes (upto almost light speed for super massive black holes) which a singularity does not.

    Black holes are always measured size wise by their event horizon since that is all we can detect. The largest so far is 18 billion solar masses.
    I completely agree. Even Stephen Hawking said that at any time the singularity lies always in the past or the future, but never in the present (in his book The Theory of Everything). What we would see in our cosmos is an ongoing process to singularity, not the singularity itself. We can never say that this is singularity, but this is going to be a singularity (as in case of blackholes, for instance) or this was once a singularity (as in case of the big bang). Therefore, singularity, a theoritical concept of zero-size, PRACTICALLY never exists in the cosmos.

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