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GIGanTic Collision

  1. Jul 22, 2004 #1
    i was just wondering, what would happen when two GIGANTIC black holes collide (Andromeda and mIlky Way) I mean, which one would suck which one? If they do collide and become one, how will that be possible?
     
  2. jcsd
  3. Jul 22, 2004 #2
    They just hit each other and combind.
     
  4. Jul 22, 2004 #3

    chroot

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    Neither one "sucks" the other. Black holes don't "suck." They gravitate exactly like any other body of the same mass would. The only difference between a one solar mass normal star and a one solar mass black hole is size: the black hole is much smaller.

    When two black holes collide, they simply merge into one.

    - Warren
     
  5. Jul 23, 2004 #4
    Since when is (Andromeda and mIlky Way), black holes? Or do you mean what might be in there center? :smile:
     
  6. Jul 23, 2004 #5
    i meant, andromeda and milky way galaxies are bound to collide. I was reffering to their supermassve black holes, sory, i forgot to mention that point
     
  7. Jul 23, 2004 #6
    another point i wanted to get cleared was, if stars are just balls of gas, then that would mean, when two galaxies collide, there isnt much explosion, just all the stars merging with each other i suppose. right?
     
  8. Jul 23, 2004 #7

    Phobos

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    Actually, the 2 galaxies mostly pass through each other without many direct collisions at all. Galaxies are mostly empty space, so it's a bit like 2 clouds of gnats that pass through each other. HOWEVER, there are significant gravitational disturbances. The shapes of the 2 galaxies will be dramatically changed (no more nice spirals). Also, a new wave of star formation will occur as long-quiet nebulae are shocked.
     
  9. Jul 23, 2004 #8

    Phobos

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    Any idea how much energy would be released (e.g., in the form of gravitational waves)? Any significant affect on the surrounding region?
     
  10. Jul 23, 2004 #9

    Nereid

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    If the galaxies have significant gas (and dust) clouds, then a collision/merger will produce spectacular fireworks - while the stars will simply pass each other by (with an exception of ~1 in a million), the gas clouds will collide, creating monster shock waves in the gas. In turn, this will trigger an intense burst of new star formation (as Phobos said), with quite a few massive stars that will die quickly and produce supernovae ... further heating and compressing the gas, and triggering yet more fireworks.

    If the galaxies are essentially gas free, the collision/merger will be pretty uneventful (except for tidal disruption). Unless the SMBH collide.

    There are a number of nice piccies of galaxy collisions on the Hubble website, as well as in the Astronomy Picture of the Day archive. You might also find a (radio?) piccie of two merging galaxies, with both nuclei having intense accretion disks and jets (associated with the SMBH). In some shortish time (like a hundred million years or five), the SMBH will collide/merge. Fortunately, I won't be here to see it!
     
    Last edited: Jul 23, 2004
  11. Jul 23, 2004 #10
    how does the math work on HUGE BHs combining
    don't you get a intencely larger BH then a simple
    addition of the starting masses do to the near lightspeed impact
    and resultant increase in mass/energy of the combined speeds
    also is not a QUASAR a possible result of the accreation disks being eaten by the high speed BHs as they get near each other in the final part of their dance
     
  12. Jul 23, 2004 #11

    chroot

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    Nothing says black holes have to be moving at near light speed to merge; in fact, they're normally be moving much less than light speed. The resulting black hole is actually less massive than the sum of its parts.

    And no, a quasar is just an active galaxy -- a juvenile galaxy whose primordial black hole is still swallowing lots of matter in the core. As the galaxy gets older it quiets down.

    - Warren
     
  13. Jul 23, 2004 #12

    i always thought that quasars were HUGE stars, spinning at great speeds. And isn't it quasars which seems to "blink" many times in a second? Im surprised to know, galaxies "blink" and turn that fast. Well, i guess that is what this forum is for, learning new things.
     
  14. Jul 23, 2004 #13

    Nereid

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    Perhaps you're thinking of pulsars?
     
  15. Jul 23, 2004 #14
    I thought the gravity of a BH would accellerate infalling matter to near light speed, at such speed the mass increases, so the impact energy is much higher then the rest mass also time is streached by the high speeds


    if no mass increase effect how do they get a multi million solar mass BH to start with

    and how could mass be less then the two starting masses as stuff cannot excape a black hole

    on QUASARs my guess is they are TWO or more black holes moving very fast
    inside each others dust disks eating huge amounts of matter at a very high rate in the final dance before the collision and after impact the show is over
     
  16. Jul 24, 2004 #15

    chroot

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    No. Matter does not have be travelling at light speed to cross the event horizon. Imagine you had a rocket that was capable of producing enough thrust to counter the force of gravity from a nearby black hole. Imagine that the rocket is initially stationary with respect to the black hole, its engines firing to counter the black hole's gravitational force. If you shut the engine off for a few minutes, you'll gain a few meters/second downward velocity. If you then turn the engine back up to full thrust, you won't accelerate anymore (since again the net force will be zero). You'll slowly fall into the black hole, maintaining that few meters/second the whole way down.
    Several million solar masses of material fall into it.
    You might be surprised that two magnets weigh less when stuck together than when pulled apart. When you pull the magnets apart, you add energy to the system, which manifests itself as mass. Similarly, four hydrogen nuclei weigh more than the helium nucleus formed by their fusion.
    You are incorrect. This is not the situation in many galaxies at all. Most galaxies have only a single black hole at their centers.

    - Warren
     
  17. Jul 24, 2004 #16
    a black hole is basically like an infinately dence planet... you could take a humungous planet thats not even as close as dence and get the same gravity out of it.

    am i right?
     
  18. Jul 24, 2004 #17

    chroot

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    lslars31,

    Yes, that's correct. There's no difference in the gravity of a black hole and a planet of equal mass. The only difference is that the black hole is compact enough to cause an event horizon to exist. An event horizon is the surface surrounding the mass at which the escape velocity equals c.

    - Warren
     
  19. Jul 24, 2004 #18
    yes BUT nothing falls slowly in to the earth in a much much smaller gravity well and I am unaware of any brakes on a BH esp one falling in to a multi-million solar mass BH
    a few meter /per second may be true for a rest mass at an event horizon for the first second, over a few minutes no as seconds add up BUT the pair of black holes willnot be at rest or slow at that point
    what is the ratio of excape V to infalling V for a BH
    if a few solar mass BH has a excape V of greater than light speed does not a bigger one have a higher excape speed and a higher accelleration do to G tooo


    you have been in a quasar resently?? yes many galaxies have quite centers and a single black hole at their centers, now, BUT they are NOT QUASARs, now,
    some strange event causes the quazar and then it ends
    a pair or more of BHs coming together is my BEST GUESS
    and once they go inside the EH the show is over

    if simple dust falling into a BH could power a quasar then there should be more smaller quasars
     
    Last edited: Jul 24, 2004
  20. Jul 24, 2004 #19

    chroot

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    My point, ray, is that objects do not need to fall into a black hole at near light speed. They may, of course, but they don't have to. There are many ways that two black holes could happen to merge, and not all of those ways requires the two black holes to be in relativistic motion with respect to each other.

    Futhermore, you should discontinue posting your "best guesses" to the main physics forums here. Your guess is not correct.

    - Warren
     
  21. Jul 24, 2004 #20

    Nereid

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    quite so, if the falling object had - relative to the BH - exactly zero transverse speed to start with. Since that's extremely rare, nothing will fall straight into a BH, rather spiral in. On its way it will likely encounter all manner of things to slow it down - other matter spiralling in, photons, debris from collisions, ...

    In the case of two SMBH, nuclei of galaxies for example, the relative transverse speed will be enormous, many km/s, so they will orbit round the common centre of mass, spiralling in as enormous amouts of gravitational radiation is emitted and the binary loses energy.
    If you have any observational results showing that quasars are, in fact, binary SMBH, please share them with us.

    The results of surveys such as 2dF point to something called pure luminosity evolution for quasars - from about z~=3 down, quasars seem to become less intrinsically luminous. I'm not sure how well theories are consistent with the actual data, but it's suggestive of the SMBH slowly consuming the available 'fuel' and becoming dimmer.
    There are plenty of 'small quasars', they're called (variously) BL Lac objects, Seyfert galaxies, and AGN galaxies. :smile:
     
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