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Collision of black holes

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  1. Jul 29, 2015 #1
    Hai pf,
    I had a doubt? we were well known about blackholes still it act as a mysterious one.
    Well my question is about collision of two black holes. what happens if a highmass of blackhole colloide with lowmass of blackhole? Is the highmass blackhole will suck the low mass black hole? Or else they two combine to form a massive one?If the gravitation is more for both what will happen?what may be the resultant? Is there any possibility to measure the force excerted in the blackhole?
     
  2. jcsd
  3. Jul 29, 2015 #2
    The nature of the collision is key. Is it a direct hit (trajectories of centers coincide), or will the black holes be orbiting each other in the process?
     
  4. Jul 29, 2015 #3
    Is the destruction will be more?
     
  5. Jul 29, 2015 #4

    Chronos

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    Based on known physics, black hole collisions should occur via inspiralling and head on collisions should be exceedingly rare. The cosmos is a very big place and black holes are vanishingly small on cosmic scales. That aside the consequences should be remarkably similar - the two will coallesce into a combined sum mass black hole. a BH is not a solid body like a star or planet and offers no 'surface' to collide with. There would likely be some nominal increase in accretion disc emissions in a high speed'collision', but, it otherwise is expected to be quite unremarkable. Interstellar collisions are exceptionally rare events, be it stars or black holes. It is highly unlikely any such event between unbound bodies [e.g. other than within gravitationally bound star sytems] has ever been observed.
     
  6. Jul 29, 2015 #5
    Thank you.
     
  7. Jul 29, 2015 #6

    HallsofIvy

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    Why "spiraling in"? Black Holes would still obey gravitational laws and so must at least approximate conic sections. "Spirals" don't seem to be possible.
     
  8. Jul 30, 2015 #7
    May i know what does the conic section refers?
     
  9. Jul 30, 2015 #8

    Chronos

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    Orbital decay
     
  10. Jul 30, 2015 #9
    Thank you
     
  11. Aug 4, 2015 #10

    George Jones

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    When two black holes "collide", they merge, i.e., when they get close enough, their event horizons merge. This happens in accordance with Hawking's second law of black hole mechanics, which means that the surface area of the resulting black hole cannot be smaller than the sum of the surface areas of the original black holes. This is a special case of the second law of thermodynamics, entropy never decreases.

    This is state-ot-the-art research stuff for an important astrophysical phenomenon (black hole mergers) that has been, and is being, studied extensively. As a (post)grad student in 1992, I attended a relativity conference, and Kip Thorne gave a talk on this. He said that the race was on for which occur first: 1) LIGO would observe this experimentally; 2) theorists would calculate the details of the expected signal. In 2005, the theorists won, but there still are loads of research calculations that need to be done.

    This is very difficult computational stuff; see the Physics Today article "Binary black hole mergers",
    http://w.astro.berkeley.edu/~gmarcy/astro160/papers/binary_black_hole_mergers.pdf

    This article is intended for folks who have a university physics background, but, by skipping the maths, I think much of the article can be appreciated by a wider audience.

    Figure 2 shows a merger.

    What happens in the classical model of a hydrogen atom, i.e., an electron orbiting a proton? The electron spirals into the proton, because the system radiates away energy as electromagnetic radiation. A system of two black holes emits gravitational radiation, hence the in-spiral. This effect has been observed for the orbits of binary pulsars.

    "Conic section" is the name given to a curve that is either a hyperbola, parabola, or ellipse. They are given this name because these are the types of curves that result when planes intersect cones.
     
  12. Aug 4, 2015 #11

    HallsofIvy

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    Careful now, I am not sure if Chronos is responding to praveena's post or mine.

    "Conic sections" are circles, ellipses, parabolas, and hyperbolas (a single point, single line or two crossed lines are "degenerate" comics).
    They are so called because if you slice a cone, at different angles, with a plane, the cross section is some form of "conic section".

    It can be shown that an object moving under a central force, that falls off as the distance to that center, squared, with NO other force, moves along a "conic section". In order to get something like a spiral, which is not a conic section, there must be some other force, such as air resistance, that "decays" the orbit.

    However, we are talking about black hole collisions. Where would the decaying force come from?
     
  13. Aug 4, 2015 #12

    Chronos

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    An orbital decay trajectory is a 3 dimensional conic section.
     
  14. Aug 5, 2015 #13
    How can you say that it may be a hyperbola? For hyperbola the two ends become infinity and there is no area existed. while calculating the conic section area, the mathematical expression could become complex?
     
  15. Aug 5, 2015 #14

    George Jones

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    Look at the figures

    http://math2.org/math/algebra/conics.htm

    and imagine that the cones extend up and down forever.
     
  16. Aug 5, 2015 #15
    I can't understand your above lines? can you explain it detail?
     
  17. Aug 5, 2015 #16

    George Jones

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    Newtonian gravity is an inverse-square force, i.e., its strength is inversely proportion to the square of the distance between the masses. For inverse square forces, unbound orbits are either hyperbolas or parabolas, and bound orbits are ellipses or circles.

    Even though this is correct, this does not apply to case of two black holes (unless they are very far apart) for two reasons.

    1) Newton's theory of gravity does no apply to the case of two black holes, Einstein's theory of gravity, general relativity, must be used. For Einstein's theory of gravity, orbits are not conic sections. Even bound orbits do not close, they look something like a Spirograph pattern.

    2) The above does not take into account radiation. The Coulomb force between an electron and a proton is also an inverse-square force, but (classically) the orbit of an electron is not a conic section, because accelerating charges radiate away energy in the form of electromagnetic radiation. This cause the electron's orbit to spiral into the proton. Similarly, Einstein's theory of gravity predicts that a two-black hole system will emit gravitational radiation, causing orbits to spiral in.
     
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