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When blackholes merge.

  1. Does gravity force them together?

    5 vote(s)
  2. Is there a cataclysmic explosion,and they are destroyed/

    1 vote(s)
  3. Do both add there gravity,don't merge,and become a bigger one?

    4 vote(s)
  1. Apr 15, 2003 #1
    I'm asking this question to see what people think about what happens when two blackholes collide.If you want,give a reason for you answer.
    Last edited: Apr 15, 2003
  2. jcsd
  3. Apr 15, 2003 #2


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    They merge to become a bigger black hole.
  4. Apr 16, 2003 #3
    I'm not so sure about the third option, which I chose because I think it is the most correct.

    I believe they DO merge and become one big one; although, I'm not positive about this, as when galaxies merge you can still see remenants of the two or more galaxies that merged. But galaxies are much larger with their gravity spread out much more, so perhaps bh's don't merge like they do, larger gravity on a smaller spot, seems to me, that it would merge into one bh.
  5. Apr 16, 2003 #4
    could someone explain how there could be a theoretical explosion?

    like what would cause it[?]
  6. Apr 16, 2003 #5
    Well I was thinking,that if gravity attracts spacetime.spacetime is charged with energy.spacetime got charged with energy when normal matter collapsed into a singularity,when matter was forced into a point,then spacetime folded around it,decompressing matter.so it exploded into matter in this universe,since matter at the heart of a star is super heated,thus where the heat came form in the begining.but my point is,matter attract energy from spacetime,pulling it in faster than light,or light.so it curves spacetime by the sucking of energy toward a body of mass.then the matter uses this energy from spacetime to make magnetic fields.so atoms can function.so energy conservation is maintained and the particles don't gain mass.so gravity is not a attraction between two masses but the pulling of spacetime energy around ,through,behind,and in front of another mass.so gravity of a mass forces spacetime energy into motion ,the other masses atraction to moving spacetime starts the mass into motion.on the earth when you jump or something falls,its not your attraction to the earth that makes you come down,but your attraction to spacetime energy coming toward the earth that since your in the earth field you have the same field the earth does,you gravitate to to spacetime energy in motion and come back down.so when two singularity merge,once they make contact forward attraction ceases,and the only force that would force them together is the attraction of spacetime behind each one,but at that point there fields have combined as one and lost all attraction to each other ad became one field,and never merged into one.but stayed two next to each other.
  7. Apr 19, 2003 #6
    Matter interactions

    Results of aggregated matter interactions depend on their paths.
    Direct collision generates an explosion and a roughly symmetric combining of aggregate mass.
    Indirect collisions can result in various levels of explosion with asymmetric, whirling dispersion and possibly separation of mass.
    Misses may result in mutually altered directions ranging from bent paths to various types of mutual orbits.
  8. Apr 19, 2003 #7


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    Howdy Darl!

    I think the trouble with talking about "explosions" with regard to Black Holes is that explosions expand outward, and nothing can expand outward from a BH.

    I voted that they combine (a. "Gravity force them together"
    ), since once the central mass of each BH is inside the event horizon of the other, they cannot stop moving inward toward one another untill they occupy the same point in spacetime. Trajectories before collision should not matter since inside the EH, all orbits point toward thwe center.
  9. Apr 20, 2003 #8
    I agree with Lurch. (But I chose choice 3) Black holes that collide don't explode, but they will become relatively denser than before. Could any two black holes that collide become a singularity?
  10. Apr 21, 2003 #9
    If matter and energy are interchangable,then the singularity is a super particle of all the energy that was forced into one point.when there being forced together,why would'nt the bounderies of the singularity holding the energy rupture and releases all the stored energy before the two singularitys can combined.
  11. Apr 21, 2003 #10
    Lurch,I think the trouble with talking about a BH as something from which nothing can expand outward is that it abnegates infinite time. I am unwilling to forsake infinite time, therefore I believe massively compacted aggregates of matter are instable, due to their electron-positron composition. Eventually under extreme compaction, one or more pairs of like particles will be so close together that repulsive force(s) will initiate fission.
    If the repulsive force is inversely proportional to some power of the separation distance, imagine the force created by near zero separation.
  12. Apr 22, 2003 #11
    When they do collide, wouldn't it cause a massive surge of gamma radiation or virtual particles or something? (that's what happens with globular clusters in cosmology)
  13. Apr 22, 2003 #12
    i don t believe in the singularity
  14. Apr 22, 2003 #13


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    I tend to agree. The most widely accepted models of black holes all agree that time dilation prevents objects falling toward the center from ever actually "reaching" it. As an object approaches the center, time slows down so drastically that the final moment before "arrival" at the center takes forever. If these models are correct, then I think that should mean that the two central masses of the two colliding black holes would never quite make contact with one another.

    However, it should also mean that the final moment of the collapse which forms a black hole should also take forever. The surface of the collapsing mass should continue to progress toward the center, where its dimensions would become "0". However, this progressive shrinking should take place more and more slowly, with the final moment before "vanishing" being of infinite duration.
  15. Apr 24, 2003 #14
    actually there are two reference frames that time exist in to the falling object.the one on the outside and the object falling.to us on the outside time is constant so as we see the object falling in time slows down for it and will move slower and slower never reaching it.but to the object falling it would instantly hit at the speed its falling.as time to us runs normal and we see the object suspended.the millions of our years on the outside pass in seconds to the falling object.
  16. Apr 24, 2003 #15
    What's so paradoxical about singularities?
  17. Apr 29, 2003 #16
    How about none of the above? They may merge and add their gravity but they could not get "bigger" only more massive
  18. Apr 29, 2003 #17


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    J.A.Wheeler pointed out in a recent book that there is an
    elegant pythagorean thing that happens when they merge.

    Say we are talking about nonrotating uncharged BH so the radius is simply related to the mass by 2GM/c^2

    Say the two collide

    And during the process of spiraling into each other they radiate away as much possible gravitational energy. The gravity waves would be pretty energetic as they are merging and carry away quite a bit of energy.

    finally the two singularities merge into one and everything settles down and you have another larger normal black hole

    now the good part:

    the radius is equal to the pythag. "hypoteneuse" of the right triangle made with the two input radiuses (!!!!)

    so if the two incoming radii are r and R, the new radius is
    sqrt(r^2 + R^2)

    this blows the mind, or? it is wonderful.

    it tells how much mass is radiated off as grav waves.

    because if there was no loss of mass then the new radius
    would be r+R

    but if there was no loss of mass there could be no merger, they would be just whizzing past. for mutual capture there must be
    a loss of energy

    recently saw this discussed on web, maybe usenet,
    does anyone want a link (would have to hunt for it)
  19. Apr 29, 2003 #18


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    this is a link to a page that has a quote from Wheeler's 1998
    book that talks about this pythagorean thing with the black hole radiuses (when they collide) so you get Wheelers own words.

    "If two balls of putty collide and stick together, the mass of the new, larger ball is the sum of the masses of the balls that collided. Not so for black holes. If two spinless, uncharged black holes collide and coalesce - and if they get rid of as much energy as they possibly can in the form of gravitational waves as they combine - the square of the mass of the new, heavier black hole is the sum of the squares of the combining masses. That means that a right triangle with sides scaled to measure the masses of two black holes has a hypotenuse that measures the mass of the single black hole they form when they join. Try to picture the incredible tumult of two black holes locked in each other's embrace, each swallowing the other, both churning space and time with gravitational radiation. Then marvel that the simple rule of Pythagoras imposes its order on this ultimate cosmic maelstrom." p.p. 300-301 Geons, Black Holes, and Quantum Foam by J.A.Wheeler 1998

    The rest of this post is just a kind of footnote to the above Wheeler quote. The reviewer Sarfatti's words about this passage were moderately interesting so I quote an exerpt from him too:

    "... Wheeler points out that Bekenstein showed that this Planck area of 10^-66 cm^2 [of a Planck Mass Black Hole] corresponds exactly to one c-bit of classical Shannon on the surface (event horizon) of a classical black hole. Note that a classical c-bit is not the same as a quantum q-bit of information. Wheeler also discusses Christodoulou's marvelously simple profound new application of the ancient Pythagorean theorem....
    However, oddly enough, Wheeler does not, it appears, make the obvious, to me at least, connection between Christodoulo's Pythagorean theorem and Bekenstein's black hole information theory that the black hole horizon's surface area is proportional to the c-bits it has swallowed up. Wheeler's discussion of Bekenstein is later on p. 314. Clearly, Christodoulo's theorem simply means that the information of each black hole add linearly when they fuse together and attain dynamical equilibrium. ..."
  20. May 2, 2003 #19
    Note that if two ordinary masses with radius r1 and r2 collide (say, two planets, or water droplets merge) then radius of resulting mass is NOT r1+r2, but rather (r1^3+r2^3)^1/3.
  21. May 2, 2003 #20


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    Thanks! that is a good way to see a way that the black holes differ from droplets!
    In Wheeler's case of the two black holes (which get rid of mass-energy by gravity waves as they coallesce)
    the new mass is
    sqrt (m^2 + M^2)
    and so the new radius is
    sqrt (r^2 + R^2).

    But with the two droplets the new mass is
    for all practical purposes
    and as you point out the new radius is
    cuberoot(r^3 + R^3)
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