- #1

chosenone

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I'm asking this question to see what people think about what happens when two black holes collide.If you want,give a reason for you answer.

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- Thread starter chosenone
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chosenone

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- #2

mathman

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They merge to become a bigger black hole.

- #3

kyle_soule

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I believe they

- #4

screwball

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could someone explain how there could be a theoretical explosion?

like what would cause it[?]

like what would cause it[?]

- #5

chosenone

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- #6

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.

- #7

LURCH

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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 until they occupy the same point in spacetime. Trajectories before collision should not matter since inside the EH, all orbits point toward thwe center.

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chosenone

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- #10

If the repulsive force is inversely proportional to some power of the separation distance, imagine the force created by near zero separation.

- #11

Originally posted by chosenone

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)

- #12

lethe

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i don t believe in the singularity

- #13

LURCH

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Originally posted by lethe

i don t believe in the singularity

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.

- #14

chosenone

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- #15

What's so paradoxical about singularities?

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Royce

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- #17

marcus

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Originally posted by chosenone

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)

- #18

marcus

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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. ..."

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marcus

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Originally posted by Alexander

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

m+M

and as you point out the new radius is

cuberoot(r^3 + R^3)

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