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I Do black holes have colour?

  1. Aug 4, 2015 #1
    Well, do they?
    Also: black holes, unlike elementary particles, have continuous distribution of rest mass, because they are free to absorb photons and gravitons of arbitrary mass, and kinetic energy of particles they capture.

    If two Kerr or Newman black holes have equal spin, which happens to be a half-integer one, how close do their rest masses have to be for them to behave as indistinguishable fermions?
     
  2. jcsd
  3. Aug 4, 2015 #2
    A black hole is black.
    It absorbs all photons at every wavelength and emits none.
     
  4. Aug 4, 2015 #3
    None that you could see. Theoretically, black holes emit Hawking radiation, the wavelength of which is determined by the size of the black hole. According to wikipedia, the wavelength of the black hole's black body radiation is 16 times it's schwarzschild radius. So for the supermassive black hole at the center of our galaxy would radiate with a wavelength of 200million kilometers. So extremely low energy radio.

    The smaller the black hole, the hotter it gets, so when a micro black hole evaporates, it emits a gamma ray. There is a conceivable size that for a moment a black hole might emit a photon in the visible spectrum.
     
  5. Aug 4, 2015 #4

    mfb

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    A black hole with a mass of about 1019 kg would have its peak emission in the visible light range. At that mass, its remaining lifetime is roughly 1 second. Which also means its brightness would be comparable to the whole Milky Way at 1036 W.
    Well, obviously it would be visible before that, but with stronger infrared emission (compared to visible light) then.

    It is unclear how black holes would fit to the quantum-mechanical framework. Their mass could be quantized in some way - we just don't know.
     
  6. Aug 4, 2015 #5

    Gaz

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    Regardless of it being black and absorbing all light that passes its event horizon it should create a gravitational lens though right? Making it look like a bubble in space ?
     
  7. Aug 4, 2015 #6
    Yes it should create a gravitational lens.
    Actual gravitational lenses have been observed, but as far as I know they are attributed to large galaxy clusters rather than black holes though.
     
  8. Aug 4, 2015 #7

    mfb

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    The "focal length" of such a black hole would be very short I think.
    Deflection of light by black holes has been observed indirectly - in binary systems or even just to describe the accretion disk it is an important part for the description of the system.
     
  9. Aug 4, 2015 #8

    PeterDonis

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    You're mixing models. The Kerr-Newman black hole geometry is classical; there's no such thing as a "fermion" (or "boson" for that matter) in this model. A Kerr-Newman hole can have a continuous infinity of possible masses, and each one is different.

    As mfb noted, we don't currently have a quantum theory of black holes, because we don't have a quantum theory of gravity. So even if we revise your question so it doesn't assume a classical model that isn't applicable, your question is not answerable at our current state of knowledge.
     
  10. Aug 4, 2015 #9
    If a quark falls inside the event horizon of a black hole, does the black hole acquire a colour which enables the now coloured black hole to be a source of a gluon chain and pull in the rest of the quarks and gluons of the hadron?
     
  11. Aug 4, 2015 #10
    You are confusing color with color charge. Color is a component of photons and only photons, it's it's frequency. Color charge is a component of quarks and gluons and has nothing to do with what it actually looks like.

    As for pulling in quarks, I don't think so. I don't think quarks actually have a defined position within a hadron. So if you have a meson, I don't think you can be know that quark is on one side of the event horizon and one is on the other side. Don't quote me on that though, not totally sure. Definitely sure about the difference between color and color charge though.
     
    Last edited: Aug 4, 2015
  12. Aug 4, 2015 #11

    mfb

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    Would probably need a quantum theory of gravity for a better answer. In practice, there is no way a part of a hadron could remain outside.
     
  13. Aug 4, 2015 #12

    Vanadium 50

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    A black hole is a color singlet. Since there are no free quarks, a single quark cannot fall into one.
     
  14. Aug 5, 2015 #13

    vanhees71

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    Well, theoretically you can have a black hole with color (in the sense of the charge of the strong interaction), and funnily enough GR + a nonabelian gauge theory has black holes with hairs, which is different from GR + Maxwell (abelian gauge theory), where black holes have no hairs according to a famous theorem discovered by Wheeler.

    https://en.wikipedia.org/wiki/No-hair_theorem
     
  15. Aug 5, 2015 #14

    PeterDonis

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    The original "no hair" theorem didn't say no hair, period; it said no hair other than mass, charge, and angular momentum. Charge, of course, comes from GR + Maxwell, so, strictly speaking, GR + Maxwell does have hair. The hair in GR + Yang-Mills is basically the non-abelian gauge theory version of the GR + Maxwell hair; but AFAIK this Yang-Mills hair is not color charge, exactly, it's actually more like a "magnetic" charge than an "electric" charge.
     
  16. Mar 25, 2016 #15
    So if a hadron passes event horizon so that one quark winds out just inside the horizon, what does the rest of the hadron do?
     
  17. Mar 25, 2016 #16

    ChrisVer

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    even at the case quarks would matter, I guess it would split into several hadrons...
     
  18. Mar 25, 2016 #17
    The problem is that any number of hadrons would have to be white. Which the part of the hadron left outside event horizon is not.
     
  19. Mar 25, 2016 #18

    Vanadium 50

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    So if a magnet passes event horizon so that one pole winds out just inside the horizon, do I have a monopole?
     
  20. Mar 25, 2016 #19
    Magnetic poles are not quite so assigned to specific particles.
    Since a black hole can have angular momentum and electric charge, but no other hair, what happens to the dipole magnetic field of an electron when it falls in a black hole? Looks like the whole field with all field lines falls in the hole leaving nothing outside, right?
     
  21. Mar 25, 2016 #20
    Black holes have a temperature and are the perfect black body emitter. The temperature and therefore color depends on its size. Oops newjerseyrunner already covered it.
     
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