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Einstein equation and particle jets

  1. Mar 21, 2012 #1
    Does any one know if Einstein equation predicts the existence of particle jets fired by massive black holes observed by NASA from active galaxies?

    If yes, what would be the predicted relation between the black hole mass and rotation speed to the flux of matter ejected, how long these jets continue to fire particles and what is the total mass ejected by the jets? Is the total mass bigger or smaller than the matter that falls in to the black hole?

    If not, what is missing in Einstein equation?

  2. jcsd
  3. Mar 21, 2012 #2


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    People mention rotating magnetic fields as being responsible, but no one has come up with a complete explanation of what really produces the jets.
  4. Mar 21, 2012 #3
    Hi Bill,

    I found interesting article discussing Penrose process-


    The authors conclude that black hole rotational energy can be reduced and extracted by the escaping particles where the escaping particles becomes more energetic than the first falling in particles.

    If we generalize this conclusion, black holes might be seen as energy sources, and since energy and matter are related, this also means that black holes might be seen as sources of matter ejected to space, where more matter is injected out than falling in -
    Does it make sense to you?
  5. Mar 21, 2012 #4


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    The classic paper on how the jets are formed is Blandford and Znajek, 1977 - see the link below. It is believed that a rotating black hole with a strong magnetic field is responsible. People are actively working on trying to simulate the formation of the jets, but it is not yet completely understood. A more recent paper is also attached below. The simple answer to your question appears to be yes, Einstein's equations of GR, together with Maxwell's equations, do explain the jets.


  6. Mar 21, 2012 #5
    OK, and thanks for the paper's pointers!

    What do you think on the other questions and particularly - Is the total mass fired by the jets bigger or smaller than the total matter that falls in to the black hole?
  7. Mar 21, 2012 #6


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    The question of how much of the mass/energy of the jets comes from infalling material, and how much is extracted from the rotational energy of the black hole, I think is an active research topic at present, and I don't think anybody knows the answer with any confidence.
  8. Mar 21, 2012 #7
    I thought that this might be the answer (not known yet) but I was not sure.

    If black holes are active and continuous sources of matter they might replace the big bang theory that assumes that all matter was created in one singular in space and time event and such continuous and scattered all over the universe sources of matter model makes much more sense to me.
  9. Mar 21, 2012 #8


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    I think you misunderstand me. Black holes do not create mass/energy. The mass of a black hole is made up of all of the mass that has fallen into it during its lifetime. If a black hole is rotating rapidly, some of the mass/energy can be extracted from it and sent back out into the universe, but this is mass/energy that fell into the black hole at an earlier time. To repeat, they do not create any new mass/energy.
  10. Mar 22, 2012 #9
    I am not sure your answer is what field theory in curved spacetime argues. To my understanding field theory in curved spacetime allows formation of matter in curved space, and spacetime around black holes is curved.

    I think the question is quantitative, if matter is formed in very big quantities that fills the universe or is it a negligible effect that does not add much mass to the mass of the universe.
  11. Mar 22, 2012 #10


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    Are you talking about Hawking radiation? You are right that Hawking radiation allows black holes to emit particles, but the energy of the emitted particles comes from the mass of the black hole - it doesn't come from nowhere. In other words, if a black hole emits a particle of mass m by Hawking radiation, the black hole's mass is decreased by m.
  12. Mar 23, 2012 #11
    From what I read recently it seems that a different mechanism where the black hole rotation speed is decreased when the particles are ejected was also suggested.
    Accordingly rotation energy is transformed to mass
  13. Mar 23, 2012 #12


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    Correct. This is what I said earlier that with rotating black holes it is possible to extract some of the mass/energy of the black hole and send it back out into the surrounding universe. However, since mass and energy are equivalent, this does not "create" any mass/energy. If we have a black hole of mass M, and we extract some quantity of mass/energy Delta-M from the black hole, then the mass/energy of the black hole is decreased by an amount Delta-M. Furthermore, this Delta-M is made up of mass/energy that fell into the black hole at an earlier time. No mass/energy is created.
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