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Black holes

  1. Apr 26, 2008 #1
    i was reading about an article about the keck observatory and its use of a laser to observe super massive black holes at the center of the galaxy. they talked about how they found young stars near the black holes and how it wasnt possible. so it gave me an idea. is it possible for black holes to become destablized and revert back into stars? i mean like when a black hole comes into proximity with another black hole and gets a sling shot effect streching it out and making it more and more eliptical, and peices of it breaks of and shots back out into space and revert into stars?
  2. jcsd
  3. Apr 26, 2008 #2
    Good idea, but to our knowledge no.
    According to general relativity and the standard model -> black holes are singularities: they are points with no physical extent - i.e. the actually matter is infinitely dense, and occupies to volume. Because of that, no matter how fast its accelerated i don't think it could be distorted.
    According to string theory (and i think some others) the center of a blackhole would have some physical extent, but it would be on the planck scale... i.e. ridiculously smaller than the nucleus of a single atom. The acceleration that would be required to "stretch" out the center of the black hole would be unimaginable... not to mention that the force required to provide that acceleration would need to be pretty close to infinite.
    I like your thinking though.
    Does that answer your question?
  4. Apr 29, 2008 #3
    According to current physics and understanding the formation of a black hole via the normal pathway of supernova explosions is an IRREVERSIBLE process.

    Does not mean that there may be a possible avenue for black holes to revert back to a star - but I cant see how. The black hole would have to release material and this would require matter to break the light barrier which is prohibited by Einsteins relativity thoeries.

    The only mechanism of energy or matter escape from a black hole is described by Stephen Hawking et al in the 1970's. The Hawking radiation involves the coupling of cosmology and quantum physics. It essentially involves the separation of quantum particles at the event horizon of a black hole.

    In other words, one of the "particle/anti-particle" pairs that randomly emerges out of the void near the event horizon is dragged into the black hole whilst the other is released as Hawking radiation.

    In fact, Hawking;s thermodynamic analysis of black holes would imply that Black holes are NOT ETERNAL - they eventually evaporate away into nothing.

    So the most likely fate of a black hole is to revert into "NOTHING" - and if the universe is expanding unabated as it is then the fate of "everything" is to revert into nothing AND that includes the black hole

    who knows what will be uncovered in another 1000 or more years of scientific inquiry
  5. Apr 29, 2008 #4
    Thats the point I wanted to make. Hawking radiation is the black hole killer. However I dont fully understand the ending point of evaporation. Hawking radiation happens only to very massive objects like black holes, but if they evaporate enough they stop being black holes no? And therefore hawking radiation should no longer take place, therefore black hole - or the bundle of material thats left, shopuld stop evaporating.
  6. Apr 29, 2008 #5
    Almost. If black holes really do collapse to a point of infinite density, then it doesn't matter how much mass it has, it will always be a black hole - that is, until it has no mass --> the end result of evaporation (theoretically).
  7. Apr 29, 2008 #6

    From what I understand of black holes or cosmic singularities, its the critical density that is important - ie there has to be a critical amount of mass (or more) sqeezed into a specific volume so that space-time can be warped to such an extent that even light cannot escape - in other words the object has a region surrounding it called the event horizon that has an escape velocity equal to the speed of light.

    The LARGE HADRON COLIDER at CERN will be conducting many test this year. One of them hopes to produce "micro-black-holes" that may not last very long and hopefully they vindicate the nature of Hawking radiation.

    Once a black hole forms it becomes like a matter/energy diode - ONE WAY TRAFFIC.

    Hawking radiation is the only known postulated theory that allows for escape of particles at the event horizon of a black hole.

    If true it will mean that the balck hole will shrink - but the central singularity will remain that drives the whole evaporation process.

    In the end you will be left with ONE particle - the smallest perhaps.

    who knows about these things - mostly conjecture becasue there is very little direct evidence and observational mmeasurements on balck holes (especially the internal dynamics which at the moment are purely theoretical and mathematical analyses)
  8. May 19, 2008 #7
    Radiation temp increases as BH evaporates, it's a runaway reaction at the end. So the last photon to leave maybe contains all the remaining mass/energy (I'm guessing). I think maybe the problem is that the singularity is a product of GR. It's not really a singularity, because that would be smaller than a Plank length, so it's some quantum object. Like you said, a lot of conjecture, fun to think about but beyond my math skills.

    Related question: Hawking radiation - if one virtual particle ends up on the outside of the horizon, it becomes real and we see it as radiation. But what happens to the other? To balance the energy equation, the escaping particle must be balanced by a decrease in mass of the black hole. So does the other virtual particle turn into an anti-particle? And how would that help, you can't tell whether a black hole was made from matter, anti-matter or pure radiation (that would be difficult I think). So what falls into the BH to make it decrease in mass?
  9. May 19, 2008 #8


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    There's quite a nice explanation of Hawking Radiation here
  10. May 19, 2008 #9
    Very nice .... thanks.
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