Question: Two Black Holes Passing Each Other

[HansMustermann]

Hmm, true, I was thinking in terms of their original event horizon, and not what happens to its shape when the other is getting near. I'm going cross-eyed just trying to think what happens there, so I guess I'll just leave it to the real physicists

ETA: then again, if the event horizons touch, doesn't that make it a single event horizon, i.e., a single black hole? Even if not a spherical one?

 

[sol invictus]

ETA: then again, if the event horizons touch, doesn't that make it a single event horizon, i.e., a single black hole? Even if not a spherical one?

That's a semantic issue. Before they touch they are two, after they merge they are one, but what are they at the instant the horizons first touch?

You could ask the same question about two soap bubbles merging, and whatever answer you decide on there is equally satisfactory here.

 

[jhutchins11]

Black holes are real objects made of matter like a planet only their mass is so dense even light can not escape. Any two black holes coming anywhere near each other would simply combine and become one black hole in a relatively clean and quite fashion especially with tidal forces acting on each. If you were being sucked into one your body would be torn asunder meaning the parts of your body closer to the black hole would have much more gravitational pull being exerted than the following. The same would apply to the black hole being sucked into the black hole only there would be no tearing asunder as the gravitational pull around the perimeter would not be greater than the mass of the matter already consisting of the black hole. I don't believe the black holes would do any such orbiting either as the acceleration rate of their gravitational pull would be too exponential being greater than that of able to contain light which travels at 300,000 m/s following the guidelines of E=Mc^2, the equation for gravitational orbits and acceleration or some derivative of such.

 

[Vorpal]

Just how messy is black hole merging, anyway? I know Hawking has a theorem that forces the total horizon area to be monotonically increasing, which provides an upper bound on how violent of an event that is. But how tightly is this bound followed in reality--e..g, can one also say that the final horizon area is generally "just a bit" higher than the sum of the pre-merged horizon areas at least in "most" cases, or can be much, much higher?

One might expect the most violent collisions to be of black holes of opposite charge and angular momentum, since both charge an angular momentum decrease the horizon area of a black hole. For Kerr black holes, that indicates that no more than half the total mass can be radiated away. But that's an upper bound. Is there also a lower bound?

 

[sol invictus]

I don't believe the black holes would do any such orbiting either as the acceleration rate of their gravitational pull would be too exponential being greater than that of able to contain light which travels at 300,000 m/s following the guidelines of E=Mc^2, the equation for gravitational orbits and acceleration or some derivative of such.

Black holes orbit each other in almost exactly the same way two planets of the same mass would. The only differences relate to tidal forces and the degree of gravitational radiation.

Just how messy is black hole merging, anyway?

It's very hard to follow either analytically or numerically, but in the end it turns out to not be very messy. It's more or less what you would expect.

I know Hawking has a theorem that forces the total horizon area to be monotonically increasing, which provides an upper bound on how violent of an event that is. But how tightly is this bound followed in reality--e..g, can one also say that the final horizon area is generally "just a bit" higher than the sum of the pre-merged horizon areas at least in "most" cases, or can be much, much higher?

One might expect the most violent collisions to be of black holes of opposite charge and angular momentum, since both charge an angular momentum decrease the horizon area of a black hole. For Kerr black holes, that indicates that no more than half the total mass can be radiated away. But that's an upper bound. Is there also a lower bound?

There can't be a lower bound in general. Two extremal (maximally electrically charged) holes exert zero force on each other at rest. That makes it reasonable that they would not radiate much energy as they move towards each other. Make that motion very slow, and the total energy of the system is only slightly larger than its charge (the excess comes from the kinetic energy of their motion), and therefore only the energy corresponding to that KE could potentially be radiated away.

There might be one for uncharged holes in the absence of any other sources, though.

 

[jhutchins11]

http://www.nasa.gov/vision/universe/starsgalaxies/gwave.html

I actually did some research this time and found this link (the first on a google search ) It seems that all of us are correct in one way or another. The forces that are involved become so infinite in this stellar event that even supercomputers of these models freeze, as time begins to stand still and gravity waves propagate outward faster than the speed of light. Each of our descriptions correctness depends on the perspective you would take in relation to the two holes merging, as well as the mass of consciousness itself.

 

[sol invictus]

http://www.nasa.gov/vision/universe/starsgalaxies/gwave.html

I actually did some research this time and found this link (the first on a google search ) It seems that all of us are correct in one way or another.

Actually, no.

The forces that are involved become so infinite in this stellar event that even supercomputers of these models freeze

Nope. As of a few years ago, the merger of two black holes has been successfully simulated.

as time begins to stand still

Time doesn't really "stand still" at a black hole horizon.

and gravity waves propagate outward faster than the speed of light.

Nonsense. Gravity waves propagate at exactly the speed of light.

Each of our descriptions correctness depends on the perspective you would take in relation to the two holes merging, as well as the mass of consciousness itself.

 

[nota]

I can ''see'' gravity waves as a energy escape for the forbidden faster or even at/very near that by definition light speed problem
but donot see how the gravity wave can negate the energy = mass gain at near but sub-light speeds as those speeds are allowed

AND WE DO HAVE SUPER MASSIVE BLACK HOLES
in fact they are not rare but very common as every normal galaxy seams to have one
at it's center
so we need a way to make them and make them quickly in the very early universe

so black holes are big bang created or grow very fast very early

 

[sol invictus]

I can ''see'' gravity waves as a energy escape for the forbidden faster or even at/very near that by definition light speed problem
but donot see how the gravity wave can negate the energy = mass gain at near but sub-light speeds as those speeds are allowed

Are you asking about the collision of two black holes that were moving at relativistic speeds?

AND WE DO HAVE SUPER MASSIVE BLACK HOLES
in fact they are not rare but very common as every normal galaxy seams to have one
at it's center
so we need a way to make them and make them quickly in the very early universe

so black holes are big bang created or grow very fast very early

That's presumably due to accretion of ordinary matter onto a black hole horizon, not to black hole mergers.

 

[nota]

I have long thought BH interaction is a key bit of a quasar's light show
esp as they are a early universe show that has shutoff in our current age
and some resent papers are going in that direction so the wild effects of BH's
are getting more mainstream and less guesses now

and a billion solar mass BH needs time to grow that big
something we are NOT seeing

gravity waves are a interesting thought but hardly a proven fact
and to put 100% faith in their property's more then a little premature
lets find one first or the equally speculative graviton for that matter

I really think few in the physic community really understand a BH merger
and the = to the rest mass idea just is a guess with the real universe far stranger then most guess