# If two black holes combind together-

1. Apr 23, 2007

### magnetar

If two black holes combind together------

If two black holes combind together,the main form energy emited by this event is "gravitational waves"??

2. Apr 23, 2007

### pervect

Staff Emeritus
Offhand, I can think of any other way for them to emit energy, so I would say yes. But I don't have a reference for this statement, unfortunately.

3. Apr 23, 2007

### Red Anvil

Would it not be Rotational Energy? Because the spining of both will add together? (Though I don't know much about black holes, just what i have read, so that could be TOTALLY wrong :(

4. Apr 23, 2007

### magnetar

From the book <<black holes and time warps>>,P413 Paragraph4 .we may find some clue of this question?

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5. Apr 26, 2007

### reddragon_2oo8

Though the emission of gravitational waves would be present the thought of radiational emissions would be a better chance of what would happen. Due to the large size of black holes and the amount of energy encased in them it would result in the release of high amounts of radiation.

6. May 14, 2007

### Sojourner01

You'd probably get a fair amount of EM radiation dumped from the hot ionic matter orbiting them, too. This is generally how black holes are detected - by the behavior of the matter being drawn in, rather than the onject itself.

7. May 20, 2007

### natski

Many of the bar detectors around at the moment are limited to extremely energetic gravitational events, one example of such is two black holes combining. They have yet to record any positive results.

8. May 23, 2007

### Teresa

they'r also detected by the "wobble" of some stars that may b in orbit around the black hole... or whateva else is in orbit around the thing lol

and i say, i large explosion would happen haha not a useful piece of information, but still true =P

9. May 23, 2007

### Teresa

that is, *A* large explosion would happen... im sure i would have nothing to do with it lol

10. May 24, 2007

### ray b

if real big BHs
and in a dusty area like a galixcy core
QUASAR?
I can think of no other process that can explain
the birth life and death of quasar's
and the forming of super massive core BH's
that the process leaves behind

but non-core BH's coming together must be very very rare
as we donot see mini quasars
so maybe there is a needed size to trigger the process?
or the extra junk outside the two BH found only in a core?

11. May 24, 2007

### MeJennifer

How about using the theory of general relavitiy for this?

Shooting from the hip is not very scientific so it seems to me that if we want to answer that question in GR we have to use the equations of GR.

We could start with two identical free falling and non rotating point masses from infinity. But unfortunately we cannot even write that simple solution down in GR. Except for a few "Mickey Mouse" solutions, no metric is algebraically reducible in GR.

But what is clear is that in this case there is gravitational radiation, although actually the term radiation is a bit of a questionable description. This "radiation" not only interacts directly, it also interacts indirectly by going out and "reflect" later (4PN effects), so the situation is completely non-linear, and one even could argue, non-local.

Last edited: May 24, 2007
12. May 24, 2007

### pervect

Staff Emeritus
A head on collision may be interesting, but is not very likely. Most of the serious effort has been spent on modeling inspirals, as I think was mentioned.

Note that while we don't have any analytic solutions, and that while there are currently also problems in numerical methods with stability, we do have some general mathematical results to show that there is nothing that could be described as "nonlocal" going on. General relativity has a "well posed intial value formulation" (Wald pg 252) solutions to the equations describing the field evolution are known to exist, be unique from specified initial conditions, and to propagate in what can be described as a causal manner (see theorem 10.1.3 for the details) even though we currently have a very hard time solving them. Technically, they are a "quasilinear, diagonal, second order hyperbolic system" of partial differential equations.

13. May 24, 2007

### MeJennifer

I understand what you are saying but to claim that a theory has no non-localities but at the same time in that theory each particle's contribution to the combined gravitational field crosses the whole universe is a bit of a twist.

And then there are singularities (the real ones not the coordinate ones), do you think they are local?

Last edited: May 25, 2007
14. May 25, 2007

### FrigginGenius

Emission you say?

It would seem - to me - that since we are dealing with BHs, that nothing would be emitted no matter what happens to it. Though I think its mass would increase and consequently its gravity. So if you call it gravity waves then I suppose I would agree with the OP that the main if not only (indirectly) observable emission would be gravity waves.

I've never heard anything about the destruction of a BH or its affects on matter and its surrounding space. So I would volunteer that nothing would be emitted in that event. I would guess that the more massive BH would devour the lesser BH and we may see the wobble of a nearby star intensify or some other effect of the gravity increase but nothing from the BH(s) itself.

Thx,
Mike

15. May 26, 2007

### Chris Hillman

Trying to clarify the question

Unfortunately, I don't think this question has been very well stated. This shouldn't be read as indictment--- it can often be hard to state a question well when you are struggling with something new.

At any event, I guess that the question concerns energy radiated away in some form, not something like (in str terms) kinetic energy wrt a frame comoving with one of two colliding objects, or ejected matter (e.g. from an accretion disk or torus of dust around one of the holes, etc.). Let me try to restate it:

There are many arXiv eprints which touch on these questions, including:

http://arxiv.org/abs/gr-qc/0507014

http://aps.arxiv.org/abs/astro-ph/9908290

http://www.arxiv.org/abs/gr-qc/9905058

http://de.arxiv.org/abs/astro-ph/9801105

http://arxiv.org/abs/astro-ph/9606181

Praetorius 2005 says that in simulations of equal mass nonspinning BH mergers, "a rough calculation suggests on the order of 5% of the initial rest mass of the system is radiated as gravitational waves during the final orbit and ringdown."

Janka et. all 1999 say, concerning NS/BH mergers, "A gas mass between about 0.3 and about 0.7 solar masses is left in an accretion torus around the black hole and radiates neutrinos at a luminosity of several 10^{53} erg/s during an estimated accretion time scale of about 0.1 s."

Totani 1998 points out that due to the strong gravitational fields in NS/NS mergers, time delay plays a significant role: "A unique feature of the binary neutron-star merger scenario, in contrast to other scenarios associated to single stellar collapses, is that a time delay during binary spiral-in phase emitting gravitational waves is not negligible and makes the rate evolution flatter than that of star formation rate."

Ruffert et al. 1996 say "About $10^{-4}-10^{-3}~M_\odot$ of material lost during the neutron star merging and swept out from the system in a neutrino-driven wind might be a site for nucleosythesis".

Shibata 1997 says that in stellar cluster collision simulations, up to "0.5% of the rest mass energy may be dissipated by the gravitational wave emission in the final phase of the merger."

In one of his papers, Thorne does a back of the envelope computation suggesting that in certain merger events, the gravitational radiation luminosity can indeed exceed the EM luminosity.

Those of the above remarks which don't quite address the question as I stated it, nonetheless suggest how the restated question might be further refined.

1. The study of binary mergers as treated using a rather subtle and sophisticated theory (gtr) currently involves state of the art numerical and theoretical methods, which smart people spend years mastering in graduate school.

2. Standards here at PF are probably higher than you may have encountered at other web forums (although I think standards can be greatly improved even at PF!).

Given these facts, I'd suggest you try to refrain from stating wild guesses based on (apparently) little or no knowledge of the subject at hand. The OP's question was poorly stated, but I imagine he nonetheless wanted an informed response.

Standards here at PF https://www.physicsforums.com/showthread.php?t=5374 are probably higher than you may have encountered at other web forums (although I think standards can be greatly improved even at PF!).

Last edited: May 26, 2007
16. May 26, 2007

### FrigginGenius

Wow, I bet that didn't help a soul Chris. GJ.

17. May 26, 2007

### pervect

Staff Emeritus
This thread is spiraling downwards, out of control. I'm locking it for the nonce.