Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

This is rather a technical question for experts in General Relativity. An accessible link would be an accepable answer, although any additional discussion is welcome.

GR has well known solutions relating to single Black Holes: Schwarzchild, Rotating & Rotating with Charge. These solutions demonstrate some non-trivial GR behaviour. However do there exist any (corresponding) binary star/black hole solutions? Because of the non-linearity of GR such a solution could well demonstrate additional properties to a "solution" that simply consisted of a pair of "distant" Schwarzchild solutions glued together.

share|improve this question
1  
If you mean an analytical solution, the answer is clearly 'no'. –  Johannes Jan 22 '11 at 17:19
    
There is something called the C-metric, which has a bunch of nonphysical anomalies (including a naked line singularity), but can be thought of as a spacetime containing two black holes. But I really don't think this is what you want. –  Jerry Schirmer Jan 22 '11 at 22:54
    
Thanks everyone so far. I should point out that I was planning to question the general assumption in the repsonses that the existence of an analytical solution was "clearly no", when I discovered references to the "Double Kerr" solution. Now this is stationary and physically artificial (I think),but is still two black holes together in one analytical solution. However I accept that it is not the expected case of essentially corotating and converging BHs. It is claimed to have CTCs in some conditions. –  Roy Simpson Jan 23 '11 at 20:24
add comment

5 Answers

up vote 5 down vote accepted

For a very recent authoritative review of the numerical approach, see Centrella et. al. http://arxiv.org/abs/1010.5260
For the alternate parameterized post Newtonian approach, see Living Reviews of Relativity http://relativity.livingreviews.org/Articles/subject.html
and look for articles number 2007-2, 2006-4 and 2003-6.

share|improve this answer
    
Thanks Jim, The NASA paper at 50 pages will take some time to read, but it will be interesting to learn why so many attempts failed due unexpected blowups (software failures) in the calculations! –  Roy Simpson Jan 23 '11 at 20:42
add comment

There are no exact solutions, only approximations and numerical solutions.

Don't forget that orbiting black holes will radiate gravitational waves so any solution would have to include those and the corresponding decay of the orbit until the black holes coalesce.

share|improve this answer
add comment

According to general relativity, a pair of massive bodies that orbit each other emits gravitational waves - for analogous reasons to the reasons why accelerating charges in electrodynamics emit electromagnetic waves.

So there can't be any static solutions resembling binary stars or binary black holes. The solutions have to be non-static and a complicated system of two orbiting bodies that emits gravitational waves - and eventually collapses into one object - clearly can't be solved analytically.

These things are usually discussed numerically, see other answers. In particular, the 1993 Nobel physics prize was given for an observation of a pulsar whose frequency changes in time exactly in the right way to be explained as the loss of energy caused by the emission of gravitational waves as predicted and calculated by general relativity.

share|improve this answer
add comment

Franz Pretorius has worked on this and developed animations.

http://prl.aps.org/abstract/PRL/v95/i12/e121101

The field is numerical relativity. Matthew Choptuik also, I believe, has done work on this.

share|improve this answer
    
Thanks. I cannot access the paper directly but here is the central animation for anyone interested:physics.princeton.edu/~fpretori/qe_19_Lm2_alpha_z.mpg –  Roy Simpson Jan 23 '11 at 20:28
    
@Roy: You can probably access the paper from a computer terminal in the library at whatever major university is near your home. If you have only small to medium sized colleges nearby, check their websites to see if they have a on-line subscription to Physics Review Letters. –  dmckee Feb 1 '11 at 21:58
add comment

A way of physically thinking about this is that a two body problem in general relativity does not generally have closed orbits. If one of the bodies is very large and the other a small satellite the problem is integrable. The periapsis (perihelion) advance of the small satellite is repeated with each orbit, which makes the problem integrable. If the two bodies are of comparable mass the orbits of the two are perturbed in a manner which emulates a third orbiting body in Newtonian mechanics. The three body problem is not integrable in general. The periapsis advance of either mass adjusts to the changing position of the other mass, which “emulates” the presence of a third body. Curiously, before Einstein people thought there was another planet near the sun which perturbed Mercury, what they called planet Vulcan. If the two bodies are close enough and they are in an orbit with a quadrupole moment (Keplerian orbit, ellipses etc) there is the emission of gravity waves. Gravity waves are mass-energy and contribute to the gravity field. So a two body system in effect generates what might be thought of as a third body, or N-bodies.

share|improve this answer
    
actually this result makes me think of a conjecture I have been forming recently that the behaviour of a two body system (approx equal mass) in General Relativity is essentially a Chaotic Problem (evolution depends precisely on initial conditions). –  Roy Simpson Jan 23 '11 at 20:39
    
In a related manner I did some calculations related to this a couple of years ago. General relativity amplifies chaos. More to the point general relativity amplifies Lyapunov exponents. If there is a relativistic orbiting body, similar to Mercury, and another planet further out. The Newtonian case is chaotic, but with one of the planets general relativistic the chaotic dynamics is amplified. –  Lawrence B. Crowell Jan 23 '11 at 23:31
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.