When Galaxies collide, supermassive black holes?

[The Peon]

I would like to know what happens to the supermassive blackholes in the center of galaxies when they collide. Do the two holes instantly join like 2 drops of water, or do they sort of "rip" at each other as they pass between each other?

[Mobius]

When two galaxies collide the actual probabilities of stars, black holes etc.. colliding is slim. The galaxies completely change due to gravitational interactions.

[[Tycho?]]

Well for a black hole there isn't a whole lot to rip at. If it was a Kerr (rotating) black hole then you might get a bit of a bulge in the event horizon... maybe.... but I wouldn't count on it. Once one of the black holes enteres the others event horizon, they are essentially the same thing.

 

 

Wait a minute. Ok, so two black holes merging, big and small. Lets say the smaller singularity has just passed over the event horizon of the larger black hole. Yet there would be something of a bulge; if an observer was orbiting the larger black hole, the observer would notice a stronger gravitational attraction when he was over the point the smaller singularity had just entered.

 

Here I just whipped up a paint diagram

http://i23.photobucket.com/albums/b390/Traxus/Blackhole.gif

 

I dont see how this can work, because it would allow us to observe what was inside the event horizon of the large black hole; we would know a mass is present, and would even be able to tell that its a black hole due to the pressence of a singularity "bulging" outwards. Could someone point out to me why this is incorrect?

[Mobius]

If two supermassive black holes were to merge you would get a larger supermassive balck hole. This event could surely only be detected by the large gravitaional waves it would produce but I don't think this is possible at the moment.

[The Peon]

']

 

...I dont see how this can work' date=' because it would allow us to observe what was inside the event horizon of the large black hole; we would know a mass is present, and would even be able to tell that its a black hole due to the pressence of a singularity "bulging" outwards. Could someone point out to me why this is incorrect?[/quote']

 

Precisely why I asked. I figured we could actually see what is "inside" the hole as it "ripped!" *is suddenly very curious*

[Mobius]

As I stated we could not observe a black hole merging except the gravitational waves released. This is a good article (albeit from 3 years ago...)

 

http://www.spaceref.com/news/viewpr.html?pid=8945

[[Tycho?]]

Yes, we arn't talking about detecting such an event however.

[[Tycho?]]

bump

[Martin]

'']bump

 

I am curious Tycho. What bump-reason did you have in mind? I can think of several reasons to bump, and keep this thread handy, but what was your particular reason?

 

what I see as valuable here is the link that Möbius supplied

http://www.spaceref.com/news/viewpr.html?pid=8945

 

this gives observational evidence of BHs merging. this is something

that interests me because I hadn't seen evidence of it before.

By contrast, I have seen photographs of galaxy's in the process of merging

and also seen computer simulations of galaxy's merging.

 

Many if not all spiral and elliptical galaxies have central BHs

and when two galaxies merge their BHs presumably get into binary orbit.

Two BH in binary orbit will radiate away energy and eventually merge.

 

I have seen computer simulations of BHs merging----spiraling closer and closer until they coalesce and form just one. But I never yet saw OBSERVATIONAL EVIDENCE of BH merger. That is what the link here provides. So it is interesting.

[[Tycho?]]

This is why I bumped.

 

']Wait a minute. Ok' date=' so two black holes merging, big and small. Lets say the smaller singularity has just passed over the event horizon of the larger black hole. Yet there would be something of a bulge; if an observer was orbiting the larger black hole, the observer would notice a stronger gravitational attraction when he was over the point the smaller singularity had just entered.

 

Here I just whipped up a paint diagram

http://i23.photobucket.com/albums/b390/Traxus/Blackhole.gif

 

I dont see how this can work, because it would allow us to observe what was inside the event horizon of the large black hole; we would know a mass is present, and would even be able to tell that its a black hole due to the pressence of a singularity "bulging" outwards. Could someone point out to me why this is incorrect?[/quote']

[Martin]

'']This is why I bumped.

 

your picture is not right. it is too simple.

they do computer calculations for this and plot the results graphically.

I have seen some numerically generated pictures of the stages of BHs

merging. The event horizons do not stay round

 

the system forms a single event horizon that looks sort of dumb-bell and comes together in a blob and finally (as the centers coalesce) becomes round.

 

I dont know the link to those pictures, but you could probably find them by google.

 

==================

 

the whole thing happens very fast, within milliseconds IIRC

 

you quickly end up with a larger single BH

 

remember that as BH approach each other and spiral in to each other they are moving relativistically. they are going at substantial fractions of the speed of light. their motion sends out gravity waves which bleeds off the energy fast. one BH cannot stay in orbit around another. as the energy is radiated away they come in closer and closer

 

in a fraction of a second the two have spiraled in together and merged

[[Tycho?]]

Ok, but that still doesn't answer my question. I'll boil it down to its main element.

 

All mass exerts gravitational attraction over other mass. Have an example mass pass through the event horizon of a black hole, but not yet reach the singularity. It would seem to me an observer would be able to tell (if only maybe for a fraction of a second) that there is a second mass present in the event horizon, as it could be detected by its gravitational influence, however small.

 

But this doesn't jive with what I know about black holes. Namely it would allow one to get information about what is going on inside the event horizon (ie that there is a mass present) out of the event horizon, which should be impossible.

 

So, how does this work? Or does this not violate any theories at all?

[Martin]

']Ok' date=' but that still doesn't answer my question. I'll boil it down to its main element.

 

All mass exerts gravitational attraction over other mass. Have an example mass pass through the event horizon of a black hole, but not yet reach the singularity....?[/quote']

 

thanks for clarifying the question. I would like to be able to answer, but it's beyond my ken. I don't understand BHs and information well enough to reply confidently.

 

Maybe someone else can respond. too many paradoxes

[BigMoosie]

Directly between two black holes I would image the gravity would be cancelled and would be neutral, so when the event horizons pass over each other would there be a space between that was unaffected? If I am not explaining my question well please tell me. It seems quite bizarre to me.

[BobbyJoeCool]

The event horizon isn't "ripped", just moved.

 

For simplicity, we'll discuss two same sized black holes, both moving directly at the other (ie, the event horizons have equal speed in opposite directions.)

 

As they get closer, there will be a space between the singularities that the gravetational forces equilize (this point is halfway between the event horizons) because each black hole is pulling on you equaly... but here's the thing... you're not seeing into the black hole... you're seeing past the normal event horizon, but you aren't seeing inside the black hole (as the black hole really is only a singularity or near singularity). however, before the singularities actually merge, the black hole forces in every which direction (except bewteen the singularities) is still as strong if not stronger... and before they meet, there actually is an event horizon that is solid shaped on the outside (although not spherical) AND there is another event horizon if you are still between the event horizons... Because both singularities are pulling you (and light) towards it, once they get close enough, they still pull all around it to create a gravetational pull that light cannot escape from. You will never see the singularity unless you want to become a part of it...

 

If that doesn't help, I might be able to make a diagram, scan it and post it... But, it won't be completely accurate (as in persice...) but it will get the point across...

[BobbyJoeCool]

Ok... when the two singularities get to the point that it's at the point where the event horizon would be if the other black hole wasn't there (ie, the normal point of no return for light) the event horizon will once again extend all the way around.

 

To show you this... draw the two black holes at any point during the colision. Connect the singularities with a straight line (line a). Draw 4 more lines, 45°*above and below line "a" from each singularity (should be going toward the other black hole. The quadrilateral contained by the points of the singularities and the intersection of the 45° lines with the lines from the other singularity (that's a bit wordy...) is the area in which the gravety of the black holes conflict with eachother...

 

Please note that, this is using vector forces.. at the point of the intersection on the 45° lines, you are being pulled into each black hole (at a 90° angle to eachother) with equil force... The left/right force is negated, but half of that force is pulling you directly between the two blakc holes equil to the force of one of the equil sized black holes, therefore, light still cannot escape the black holes...

 

Does anyone understand what I'm saying?

[BobbyJoeCool]

']Ok' date=' but that still doesn't answer my question. I'll boil it down to its main element.

 

All mass exerts gravitational attraction over other mass. Have an example mass pass through the event horizon of a black hole, but not yet reach the singularity. It would seem to me an observer would be able to tell (if only maybe for a fraction of a second) that there is a second mass present in the event horizon, as it could be detected by its gravitational influence, however small.

 

But this doesn't jive with what I know about black holes. Namely it would allow one to get information about what is going on inside the event horizon (ie that there is a mass present) out of the event horizon, which should be impossible.

 

So, how does this work? Or does this not violate any theories at all?[/quote']

 

well... as any mass falls into a black hole, it will effect the size of the event horizon ever so slightly (as in the mass is not centralized). However, since the gravetational force of the singularity is so strong, the difference in gravety is so astronomically small, that it would take a VERY sensative device to notice it... And it would only exist for the time it takes something moving at the speed of light to reach the sinularity from the event horizon.

 

But, the discrepency still exists... But this is the same paradox as the EPR paradox... Two particles, one polarized positve, and one polarized negative, are sent off at the speed of light in opposite directions and stopped after 2 minutes (so the particles are 4 light minutes apart). You measure the polarity of the particle, and you'll know the polarity of the other particle before 4 minutes has passed... so the information has gotten to you FASTER than the speed of light, which is not possible.

 

You, of course, do not know the polarization of the other particle, you just deduce that since your particle is positive that the other one is negative... This applies here in this way... you do not observe the mass directly, but you observe a inconsistancy in the gravetational forces of the black hole (ie, slight bulge in the event horizon). In the same way, you don't know that the mass is there (because in order to know it's there you need to observe it, which is not possible), you just deduce that it is by its effects being apparent.

 

Does that answer your question?

[[Tycho?]]

well... as any mass falls into a black hole' date=' it will effect the size of the event horizon ever so slightly (as in the mass is not centralized). However, since the gravetational force of the singularity is so strong, the difference in gravety is so astronomically small, that it would take a VERY sensative device to notice it... And it would only exist for the time it takes something moving at the speed of light to reach the sinularity from the event horizon.

 

But, the discrepency still exists... But this is the same paradox as the EPR paradox... Two particles, one polarized positve, and one polarized negative, are sent off at the speed of light in opposite directions and stopped after 2 minutes (so the particles are 4 light minutes apart). You measure the polarity of the particle, and you'll know the polarity of the other particle before 4 minutes has passed... so the information has gotten to you FASTER than the speed of light, which is not possible.

 

You, of course, do not [i']know[/i] the polarization of the other particle, you just deduce that since your particle is positive that the other one is negative... This applies here in this way... you do not observe the mass directly, but you observe a inconsistancy in the gravetational forces of the black hole (ie, slight bulge in the event horizon). In the same way, you don't know that the mass is there (because in order to know it's there you need to observe it, which is not possible), you just deduce that it is by its effects being apparent.

 

Does that answer your question?

 

 

Uh, no. Since by deducing its existance I AM observing it, just as we can observe planets by the wobble in their host stars, or observe dark matter through its gravitational influences. There are tons of things that we can only observe indirectly, but as long as we can get information about the object, then we are indeed observing it. But one of the cardinial rules of black holes is that no matter what what goes on, inside the event horizon is unknown to the rest of the universe. Unless this does not apply to gravity for some reason.

[Xyph]

That seems a bit like saying that we shouldn't be able to tell how massive black holes are because the effects of the mass of the black hole can be observed outside the event horizon.

 

The event horizon wouldn't apply to gravity, since gravity isn't affected by gravity, so there's no reason why gravity couldn't momentarily leak out a bit. We still can't actually see, visually, what's going on inside the event horizon, we can just infer the existence of a mass beyond it, which we could do anyway, since more massive black holes have larger event horizons.

[BobbyJoeCool]

What I'm saying is that the information about the mass isn't comming from inside the event horizon... it's comming FROM the event horizon (and it's tiny little buldge) or the gravetational effects outside the event horizon. The actual information from the mass cannot escape and it isn't. but gravety's effects are greatened and thus you know that there is a mass inside at a point other than the singularity. But that's all you would know. You don't directly get information of the mass from the mass, but gravetational effects of the mass. Gravety is not entirly affected by the same laws that mass is (because mass creates gravety...).

 

It's a paradox just as much as the EPR paradox... you aren't directly observing the mass, you observe it's effects on the world around it. You know it's there, but again, that information comes from outside the event horizon.

 

But again, what you're saying is like saying that knowing the black hole exists is not possible because the singularity is inside the event horizon (and thus you can't know the mass is actually there...).

 

As for the wobble of planets, you aren't observing the planets... you observe their effect on the stars they orbit.

 

Gravity does not pull gravety... so gravity can escape from the black hole... (oversimplified).

 

Does that answer your question Tycho?

[[Tycho?]]

Yes, but I dont think its the right answer personally.

 

I dont see the distinction is observing something visually and observing something gravitationally. When we see something all we are seeing are photons emitted from it. When we detect something gravitationally, we detect how much it pulls on us or other objects. Different kinds of information about the object can be derived from both, I dont see why one is observing it while another is not.

 

I can accept that this does not apply to gravity. However, I'd definately want a more concrete answer than "gravity can escape, or gravity can leak out of a black hole", which are vast oversimplifications of what is actually going on. Thanks for the replys, I'll try and get one of the experts to answer this for me.

[BigMoosie]

Ok... when the two singularities get to the point that it's at the point where the event horizon would be if the other black hole wasn't there (ie' date=' the normal point of no return for light) the event horizon will once again extend all the way around.

 

To show you this... draw the two black holes at any point during the colision. Connect the singularities with a straight line (line a). Draw 4 more lines, 45°*above and below line "a" from each singularity (should be going toward the other black hole. The quadrilateral contained by the points of the singularities and the intersection of the 45° lines with the lines from the other singularity (that's a bit wordy...) is the area in which the gravety of the black holes conflict with eachother...

 

Please note that, this is using vector forces.. at the point of the intersection on the 45° lines, you are being pulled into each black hole (at a 90° angle to eachother) with equil force... The left/right force is negated, but half of that force is pulling you directly between the two blakc holes equil to the force of one of the equil sized black holes, therefore, light still cannot escape the black holes...

 

Does anyone understand what I'm saying?[/quote']

 

So when two black holes collide there is an internal as well as external event horizon for a short period? Does the internal one ever disappear?

[[Tycho?]]

This link describes my argument, ie that once an object has entered the event horizon it is no longer observable [detectable] to any outside observers.

 

http://en.wikipedia.org/wiki/No_hair_theorem

 

The only proposed problems with the theorem are quantum mechanical/thermodynamic in nature, not gravitational.

[BobbyJoeCool]

So when two black holes collide there is an internal as well as external event horizon for a short period? Does the internal one ever disappear?

 

Yes, when the singularities merge (because at EVERY time before, halfway between the singularities, gravetational force is neutral, and therefore, light could escape from one blackhole, straight into the other. And since, until they merge, there is a midpoint between them, and therefore an internal event horizon. Of course, if you are in this event horizon, you are completely screwed because the black holes will converge on where you are... and thus you cannot escape anyway...

[BobbyJoeCool]

WTF? Why did this post twice? It gave me an error message and said it wasn't posted... delete this (didn't mean to double post)