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Thread: Black hole radiation

  1. #1 Black hole radiation 
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    I have read of black holes emitting radiation when they are active.

    http://antwrp.gsfc.nasa.gov/apod/ap090419.html

    But I was just wondering how a black hole, which has gravity of such magnitude that not even light can escape it, can be emitting anything. The instant it is kicked out by the black hole, would it not be instantly be re-absorbed? So how can this radiation escape from the black hole.

    http://www.nasa.gov/home/hqnews/2007...lack_Hole.html


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  3. #2  
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    Nothing is emitted by the black hole itself. The radiation is from from the stuff outside of the black hole which is falling in. It is the high energy collisions of this material before it enters the black hole that causes the radiation.


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  4. #3  
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    Oh ok, thanks. That's what it seemed like it would logically be, but I just never actually found anything to say it. Anything I read always said "from the black hole" or "coming out of the black hole" things of that nature. Thank you for clarifying for me.
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    Quote Originally Posted by Haasum
    Oh ok, thanks. That's what it seemed like it would logically be, but I just never actually found anything to say it. Anything I read always said "from the black hole" or "coming out of the black hole" things of that nature. Thank you for clarifying for me.
    This is just another example of sloppy popularised science. It just sounds cooler that a Black Hole can emit radiation than only the boring material that surrounds it.
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    A few years ago it was found that powerful magnetic fields were whipping up particles of infalling material of black holes, so you can have two jets at near light speed from the north and south poles of the black holes. A bit like the way the magnetic storms of the sun causes prominences and sometimes sends millions of tons of matter off into space.

    Only one thing escapes a black hole and that is gravity because gravity cannot stop gravity.
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    Forum Freshman Sophie's Avatar
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    Quote Originally Posted by Dishmaster
    Quote Originally Posted by Haasum
    Oh ok, thanks. That's what it seemed like it would logically be, but I just never actually found anything to say it. Anything I read always said "from the black hole" or "coming out of the black hole" things of that nature. Thank you for clarifying for me.
    This is just another example of sloppy popularised science. It just sounds cooler that a Black Hole can emit radiation than only the boring material that surrounds it.
    What about Hawking radiation?
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    Hawking relies on two atomic particles being created next to each other. One enters the hole and the other escapes. If charged particles, the particle that falls into the black hole is neutralised at cost to the mass of the black hole.

    To put it at our level, we have a very steep hill a thousand miles long. At the 750 mile mark from the bottom, you have two cricket balls together. One rolls up hill and the other rolls down hill. Likely?
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  9. #8  
    Forum Ph.D. Steve Miller's Avatar
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    Quote Originally Posted by Cyberia
    Hawking relies on two atomic particles being created next to each other. One enters the hole and the other escapes. If charged particles, the particle that falls into the black hole is neutralised at cost to the mass of the black hole.

    To put it at our level, we have a very steep hill a thousand miles long. At the 750 mile mark from the bottom, you have two cricket balls together. One rolls up hill and the other rolls down hill. Likely?
    Don't understand, or not very likely. Why should one ball roll uphill, for 250 miles?
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  10. #9  
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    Quote Originally Posted by Cyberia
    Hawking relies on two atomic particles being created next to each other. One enters the hole and the other escapes. If charged particles, the particle that falls into the black hole is neutralised at cost to the mass of the black hole.

    To put it at our level, we have a very steep hill a thousand miles long. At the 750 mile mark from the bottom, you have two cricket balls together. One rolls up hill and the other rolls down hill. Likely?
    Yes, if you push the ball running uphill. This is exactly what happens during particle pair production. You need a photon with a minimum amount of energy to produce these particles (2 times 511 keV for an electron-positron pair). This means, the photon must have a wavelength smaller than , i.e. hard X rays or soft gamma rays. The energy that remains after the production is transformed into kinetic energy, i.e. the particles get a momentum. If this is enough to overcome the gravity potential close to the event horizon, one particle may be able to escape.
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  11. #10  
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    It's believed all black holes formed from the the collapse of certain stars will eventually evaporate, turning back to the basic elements or nothingness as it pertains to matter. Since we have not detected, possibly unable to observe this process most believe this process takes longer than the age of the Universe or has not yet happened.

    One theory, Hawking Radiation, denotes that every black hole, after a very long time, will eventually evaporate into nothing. Thus far, it is one of the few proposed theories regarding black hole evaporation, and remains a hotly debated topic. It is this theory that we will discuss here.

    However, only the smallest black holes could possibly evaporate in this way, because a black hole any larger than Earth's moon would have a larger constant intake of cosmic microwave background radiation—the electromagnetic radiation that fills the whole universe—than it would emit through Hawking radiation. Indeed, there are currently no known, nor predicted, black holes even close to being as small as our moon, and therefore, as of now, Hawking Radiation is not, technically, a viable cause of evaporation in the present universe.
    http://en.wikibooks.org/wiki/General...the_Black_Hole


    On radiation from inbound matter;


    However, if a black hole passes through a cloud of interstellar matter, or is close to another "normal" star, the black hole can accrete matter into itself. As the matter falls or is pulled towards the black hole, it gains kinetic energy, heats up and is squeezed by tidal forces. The heating ionizes the atoms, and when the atoms reach a few million Kelvin, they emit X-rays. The X-rays are sent off into space before the matter crosses the Schwarzschild radius and crashes into the singularity. Thus we can see this X-ray emission.

    Any emitted photons are trapped into an orbit by the intense gravitational field; they will never leave it. Because no light escapes after the star reaches this infinite density, it is called a black hole.
    http://imagine.gsfc.nasa.gov/docs/sc...ack_holes.html
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  12. #11  
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    couldn't a black hole connected to a white hole lose all its matter that way?
    http://s1.zetaboards.com/Conceptual_Evolution/index/

    Is the new address for speculative evolution.
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    Quote Originally Posted by Holbenilord
    couldn't a black hole connected to a white hole lose all its matter that way?
    As far as I know, there is not even the slightest indication that such objects could exist. In that sense, the expression "White Hole" is just a game of words without any real meaning. If there are "Black Holes" (remember, it is just an expression) does not mean that there have to be "White Holes" as well.
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  14. #13  
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    No, but there is nothing in physics saying they couldn't work(albeit for a few nanoseconds).
    http://s1.zetaboards.com/Conceptual_Evolution/index/

    Is the new address for speculative evolution.
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  15. #14  
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    Quote Originally Posted by Holbenilord
    No, but there is nothing in physics saying they couldn't work(albeit for a few nanoseconds).
    There isn't anything in physics prohibiting the existence of pink cows either.
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  16. #15  
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    Quote Originally Posted by Dishmaster
    Quote Originally Posted by Cyberia
    To put it at our level, we have a very steep hill a thousand miles long. At the 750 mile mark from the bottom, you have two cricket balls together. One rolls up hill and the other rolls down hill. Likely?
    Yes, if you push the ball running uphill. This is exactly what happens during particle pair production. You need a photon with a minimum amount of energy to produce these particles (2 times 511 keV for an electron-positron pair). This means, the photon must have a wavelength smaller than , i.e. hard X rays or soft gamma rays. The energy that remains after the production is transformed into kinetic energy, i.e. the particles get a momentum. If this is enough to overcome the gravity potential close to the event horizon, one particle may be able to escape.

    I can understand it if both particles escape, or both fall into the black hole, but the chance of two particles atomically close with one escaping and one falling into the black hole are about zero.
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  17. #16  
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    Pink cows exist if you shave a normal cow.

    Can black holes be quantumly entangled?
    http://s1.zetaboards.com/Conceptual_Evolution/index/

    Is the new address for speculative evolution.
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  18. #17  
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    Quote Originally Posted by Holbenilord
    couldn't a black hole connected to a white hole lose all its matter that way?

    Back in the 70's, John Taylor wrote a book called White Holes in which he believed that black holes were connected to white holes via worm holes and would lose matter that way as radiation. Apart from the fact that worm holes would probably need so much energy that even a black hole could not generate one which went beyond it's event horizon, we would probably have no black holes even a million years old as all would have exhausted their matter to the point where they literally blew up with not enough matter left to sustain a black hole. So no black holes left.

    While we do have some very powerful sources of energy in the universe (GRB's and Quasars) these seem to be "powered" by black holes which actually are "messy eaters" and lose much of what they try to swallow.
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  19. #18  
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    Quote Originally Posted by Holbenilord
    Can black holes be quantumly entangled?
    Entanglement seems to only work on particles. I don't know what would affect a black hole other than another black hole.
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  20. #19  
    Forum Freshman Holbenilord's Avatar
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    Or a supermassive black hole.

    When matter goes into the black hole, is it added to the black holes mass? That is, does the black holes gravity well increase after 'feeding'?
    http://s1.zetaboards.com/Conceptual_Evolution/index/

    Is the new address for speculative evolution.
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  21. #20  
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    When matter goes into the black hole, is it added to the black holes mass? That is, does the black holes gravity well increase after 'feeding'?
    Yip.
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  22. #21  
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    Quote Originally Posted by Cyberia
    Quote Originally Posted by Dishmaster
    Quote Originally Posted by Cyberia
    To put it at our level, we have a very steep hill a thousand miles long. At the 750 mile mark from the bottom, you have two cricket balls together. One rolls up hill and the other rolls down hill. Likely?
    Yes, if you push the ball running uphill. This is exactly what happens during particle pair production. You need a photon with a minimum amount of energy to produce these particles (2 times 511 keV for an electron-positron pair). This means, the photon must have a wavelength smaller than , i.e. hard X rays or soft gamma rays. The energy that remains after the production is transformed into kinetic energy, i.e. the particles get a momentum. If this is enough to overcome the gravity potential close to the event horizon, one particle may be able to escape.

    I can understand it if both particles escape, or both fall into the black hole, but the chance of two particles atomically close with one escaping and one falling into the black hole are about zero.
    Why? The velocity vectors of both particles are not necessarily parallel. If a magnetic field is present (very likely for Black Holes), both particles would spiral away in opposite directions because of their inverse charges. For further explanations you may want to read this:
    http://en.wikipedia.org/wiki/Pair_production
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  23. #22  
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    The particles would be atomically close. Even if their charges repelled each other, in a field of a zillion Gauss around a black hole, it would make little difference. Basically, what happens to one is going to happen to the other except on the very rarest of chances with astronomical odds.
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  24. #23  
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    Being close is not the issue here. All particle are close just after their production. There are some aspects I want highlight:

    Both particles get a kinetic energy that is the excess energy that remains after the transition of a photon to the particle pair. If the energy is higher than the escape velocity, they will never see each other again.

    Pair production is very commonly visualised in bubble chambers. The magnetic field separates the charged particles. They usually do not recombine. However, it is possible that they hit another particle causing new reactions.





    There is even a strange phenomenon called Positronium, where an electron and a positron form a semi-stable configuration. So, even if they are very close, they do not necessarily recombine. It all depends on their kinetic energy and momentum.

    Maybe a little analogue to illustrate what I mean: There are very close binary stars in the universe. According to your argumentation they should not exist, because their immediate neighbourhood should cause them to collide. The only difference is the acting force (electric = gravitational). But in those to situations, they are both attracting.
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