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    Black Holes

    Since the topic of black holes came up here a while back, I am pasting something by Stephen Hawking, the Cambridge physicist, who wrote the famous A Brief History of Time.

    "Professor Hawking explains on his own website that one of his achievements has been to show, together with Sir Roger Penrose, that Einstein's General Theory of Relativity implies space and time have a beginning in the Big Bang and an end in black holes.

    He also proposed that black holes should not be completely black, but should emit radiation and eventually evaporate and disappear.


    This is taken from an article on his upcoming 60th Birthday on the BBC website.



    #2
    What did Einstein say regarding this?

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      #3
      hehehe, this is my field, i will reply on this when i get home http://www3.pak.org/gupshup/smilies/smile.gif
      There is no salvation for the soul, But to fall in Love.
      It has to creep and crawl, Among the Lovers first.

      Imam Jallal-u-Din Rumi

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        #4
        Please do Dutch_paki. I have followed some of the astrophysics/astronomical stories over the media and would definately like to see a more qualified response or post http://www3.pak.org/gupshup/smilies/smile.gif.

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          #5
          Originally posted by hmcq:
          Since the topic of black holes came up here a while back, I am pasting something by Stephen Hawking, the Cambridge physicist, who wrote the famous A Brief History of Time.

          "Professor Hawking explains on his own website that one of his achievements has been to show, together with Sir Roger Penrose, that Einstein's General Theory of Relativity implies space and time have a beginning in the Big Bang and an end in black holes.

          He also proposed that black holes should not be completely black, but should emit radiation and eventually evaporate and disappear.


          This is taken from an article on his upcoming 60th Birthday on the BBC website.


          Well first of all, Einstein's General Theory of Relativity is: the universe is not in balance, it expends or it gets smaller. But since they belive in the Big bang ( the start of the universe), it means that the universe expends @ a very high rate.

          And the blackholes are cores of collapsed stars, with an incredible gravity. And they indeed emit radiation, At this point, both space and time stop. It's very hard for us to imagine a place where mass has no volume and time does not pass, but that's what it is like at the center of a black hole.The point at the center of a black hole is called a singularity. Within a certain distance of the singularity, the gravitational pull is so strong that nothing--not even light--can escape. That distance is called the event horizon. The event horizon is not a physical boundary but the point-of-no-return

          Black holes are truly black. Light rays that get too close bend into, and are trapped by the intense gravity of the black hole. Trapped light rays will never escape. Since black holes do not shine, they are difficult to detect.


          There is no salvation for the soul, But to fall in Love.
          It has to creep and crawl, Among the Lovers first.

          Imam Jallal-u-Din Rumi

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            #6
            When a star is burning, it holds its shape because the outward force of its radiation (light, heat, etc.) balances the attractive force of its gravity. When very massive stars stop burning, the force of gravity is so strong that not even the densely-packed mass can support itself and
            the star quickly shrinks in size until finally it is crushed, presumably to the size of a pinhead, then to the size of a microbe, and finally to a realm of size smaller than ever measured by humans. At this point, according to theory, there is infinite density. This point is called the black hole singularity

            According to Stephen Hawking, as a black hole singularity forms, "it would be an end of time for the collapsing bodyThis is because space-time (the 3 physical dimensions and the 4th dimension of time) does not exist at the singularity. A black hole singularity is analogous to what the Universe was, in theory, before the Big Bang when all matter was compressed into a very tiny point. Time, for us, began when that singularity expanded, creating 4 dimensional space-time.
            I was not sure what u wanted to know so i just gave u some info.
            There is no salvation for the soul, But to fall in Love.
            It has to creep and crawl, Among the Lovers first.

            Imam Jallal-u-Din Rumi

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              #7
              I don't think anybody understands (or at least can visualize) the state of matter in a black hole singularity. But atoms don't even survive the collapse into a neutron star, much less into a black hole.

              When a star collapses to form a neutron star, the tremendous pressure from the gravity causes something called inverse beta decay. Inverse beta decay occurs when an electron and a proton combine to make a neutron and a neutrino. So the atoms are inonized (stripped of their electrons) and the protons in the nucleus are converted to neutrons. As the pressure continues to increase, the atomic nuclei fall apart to form a gas of mostly neutrons (hence, the name neutron star). Then, the increasing pressure causes the neutron gas to pack into a crystalline solid. That's the core of the neutron star--no atoms, mostly just neutrons.

              When a star of 3 or more solar masses dies and collapses, all its matter is squeezed into a singularity--zero diameter, yet it has mass. A paradox. This paradoxical black hole singularity is reminiscent of the state of the Universe before the Big Bang _____---->Hawking
              There is no salvation for the soul, But to fall in Love.
              It has to creep and crawl, Among the Lovers first.

              Imam Jallal-u-Din Rumi

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                #8
                Dutch_Paki:

                What type of radiation gets emitted from a black hole?

                Thought astronomers detect a black hole due to non-emitting of any radiation.

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                  #9
                  No one knows yet, but its called : black energie. U can search the interner for it.
                  There is no salvation for the soul, But to fall in Love.
                  It has to creep and crawl, Among the Lovers first.

                  Imam Jallal-u-Din Rumi

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                    #10
                    If I understand it correctly the radiation that is emitted is not emmitted by the Black hole itself but it is the radition due to surrrounding matter falling into the black hole from the space outside of the event horizon. (as the matter falls into the black hole, it speeds up and starts to emit radiation, which is one way to figure out where a black hole is located).

                    Also normal quantum physics does not apply to sinularities so we can not use our current therioes to figure out what happens close to the center of the black hole. Dutch_paki, do you know if we an apply current theories/models for the event horizon.

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                      #11
                      Originally posted by hmcq:
                      If I understand it correctly the radiation that is emitted is not emmitted by the Black hole itself but it is the radition due to surrrounding matter falling into the black hole from the space outside of the event horizon. (as the matter falls into the black hole, it speeds up and starts to emit radiation, which is one way to figure out where a black hole is located).

                      Also normal quantum physics does not apply to sinularities so we can not use our current therioes to figure out what happens close to the center of the black hole. Dutch_paki, do you know if we an apply current theories/models for the event horizon.

                      What I worte in my last reply was wrong.
                      It is not called black energie!!. Black energie, is the energie that makes the universe expand.( They assume there is black energie, because there is no physical prove of that.)
                      Black holes get the energy to radiate Hawking radiation from their rest mass energy. So if a black hole is not accreting mass from outside, it will lose mass by Hawking radiation, and will eventually evaporate.
                      Dang, class time. I will go on when i get home http://www3.pak.org/gupshup/smilies/ok.gif
                      There is no salvation for the soul, But to fall in Love.
                      It has to creep and crawl, Among the Lovers first.

                      Imam Jallal-u-Din Rumi

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                        #12
                        Research has indicated that there is a super massive black hole at the center of every galaxy, including the Milky Way. Apparently, these black holes "sleep" for long periods of time.

                        Any guesses as to what happens when our black hole "wakes up"? http://www3.pak.org/gupshup/smilies/smile.gif

                        "A woman has got to be able to say, and not feel guilty, 'Who am I, and what do I want out of life?' She mustn't feel selfish and neurotic if she wants goals of her own, outside of husband and children"

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                          #13
                          could u lease tell us, what u mean by sleeping and waking up??????? http://www3.pak.org/gupshup/smilies/smile.gif, great thanx
                          There is no salvation for the soul, But to fall in Love.
                          It has to creep and crawl, Among the Lovers first.

                          Imam Jallal-u-Din Rumi

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