REVIEW
Colliding Black Holes: The Close Limit
General Relativity and Quantum Cosmology · Submitted 22 Feb 1994 · 11 references
Pith's verdict: The founding close-limit paper: the mu0 scaling is a genuine prediction, but the 'extends' in the abstract leans on an agreement the authors themselves call unexplained.
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Referee report
The paper
The paper claims
Two black holes that start out close enough to share one horizon can be treated as a small quadrupole distortion of a single black hole, and the energy they radiate is a fixed number times an analytic function of the initial separation.
The reading
What carries the argument
The load-bearing device is the reduction of Misner's two-throat data to a single quadrupole perturbation of Schwarzschild, plus the claim that this truncation is controlled. The authors argue order-by-order in $ε$ that the $ℓ=2$ piece of the vacuum equations is linear in $1-F$ (where $F$ is the conformal factor relating the Misner slice to Schwarzschild), that nonlinear terms cannot generate an $ℓ=6$ piece until higher order in $ε$, and that the argument generalizes to any $ℓ$. That lets them write the only nonvanishing metric perturbations as $H_2 = K = g(r)p(μ_0)$ with $g(r) = M^3/[8R^3(1+M/2R)]$, build the Cunningham–Price–Moncrief function $Q_1$, rescale it to $ψ = √(4π/5) Q_1/λ$ with $λ = 1 + 3M/2r$, and evolve $ψ$ from rest with the $ℓ=2$ Zerilli equation. The radiated power is then a fixed constant times $|∂ψ/∂t|^2$, as given by CPM (III-28). Separating the $μ_0$ dependence into the multiplicative factor $p(μ_0)$ is what makes a single numerical evolution sufficient.
Extended reading notes
Core claim
Starting from Misner's bispherical initial data for two momentarily static throats, the authors recast the geometry in Schwarzschild coordinates and expand in $ε ≡ 1/|ln μ_0|$. In that expansion the coefficient of each multipole is $κ_ℓ ≈ ζ(ℓ+1)/(4|ln μ_0|)^{ℓ+1}$, so at small separation the quadrupole dominates, and the deviation of the conformal factor from unity is a pure $ℓ=2$ perturbation of a single black hole. Feeding that perturbation into the gauge-invariant Cunningham–Price–Moncrief variables and evolving with the $ℓ=2$ Zerilli equation gives a radiated energy of $3.07×10^{-6}$ in units where $2M=1$, for the normalization $p(μ_0)=1$. The central claim is that the energy for any separation is therefore $E/2M = 3.07×10^{-6}[p(μ_0)]^2$ with $p(μ_0) = Σ_1(μ_0) + Σ_3(μ_0)/[Σ_1(μ_0)]^3$, and that this curve matches the full numerical relativity values of Anninos and collaborators, agreeing well beyond the small-$μ_0$ regime where the approximation was expected to hold.
Load-bearing premise
The argument that at small separation the quadrupole term alone matters, and that it can be treated by linear perturbation theory, rests on an order-by-order counting in $ε = 1/|ln μ_0|$ rather than on a controlled expansion with an error bound.
Editorial extensions
If this is right
- The radiated energy from initially close black holes is predicted analytically as $E/2M = 3.07×10^{-6}[p(μ_0)]^2$, so no separate nonlinear simulation is needed for each starting separation.
- The method predicts waveforms as well as energy: quasinormal ringing with period $8.4$ (in units $2M=1$) and a late-time power-law tail with exponent $-6$, both matching theoretical values, which gives numerical codes concrete targets to reproduce.
- The close-limit result complements the quasi-Newtonian approximation that works at large separation, so the two together, bridged by full numerical relativity, cover the whole range of initial separations.
- The same procedure can be applied to other momentarily static initial data, including data known only numerically, whenever those data represent a perturbation of a single black hole.
- Because the $μ_0$ dependence factors out exactly, the shape of the energy curve is fixed in advance and only one overall coefficient has to be computed.
Reading between the lines
- The factorization of $μ_0$ gives a coefficient-free test of any numerical relativity code: the ratio of radiated energies at two different starting separations is fixed analytically, so a code can be checked without ever matching an absolute amplitude.
- The suppression of the next multipole is only logarithmic. The $ℓ=4$ amplitude scales as $(4|ln μ_0|)^{-5}$ against $(4|ln μ_0|)^{-3}$ for $ℓ=2$, a relative factor of order $ε^2$, so including $ℓ=4$ would be a sharp probe of whether the $ε$ power counting really controls the expansion.
- The agreement persisting past the point where a common horizon forms suggests the radiation is set by how nearly spherical the exterior geometry is, rather than by the detailed shape of the merged horizon, which would make the close-limit result insensitive to the choice of initial data family.
- A practical extension is a hybrid pipeline: take any numerically constructed close-hole initial data, project out its quadrupole piece, and evolve that single function to get an inexpensive estimate of the waveform before committing to a full nonlinear run.
Original abstract
The problem of the mutual attraction and joining of two black holes is of importance as both a source of gravitational waves and as a testbed of numerical relativity. If the holes start out close enough that they are initially surrounded by a common horizon, the problem can be viewed as a perturbation of a single black hole. We take initial data due to Misner for close black holes, apply perturbation theory and evolve the data with the Zerilli equation. The computed gravitational radiation agrees with and extends the results of full numerical computations.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
The problem of the mutual attraction and joining of two black holes is of importance as both a source of gravitational waves and as a testbed of numerical relativity. If the holes start out close enough that they are initially surrounded by a common horizon, the problem can be viewed as a perturbation of a single black hole. We take initial data due to Misner for close black holes, apply perturbation theory and evolve the data with the Zerilli equation. The computed gravitational radiation agrees with and extends the results of full numerical computations.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | The problem of the mutual attraction and joining of two black holes is of importance as both a source of gravitational waves and as a testbed of numerical relativity. | background 1.00 | 0.05 | 0.04 | asserted 1.00 |
| s1 | If the holes start out close enough that they are initially surrounded by a common horizon, the problem can be viewed as a perturbation of a single black hole. | background 0.62 | 0.08 | 0.05 | asserted 0.77 |
| s2 | We take initial data due to Misner for close black holes, apply perturbation theory and evolve the data with the Zerilli equation. | method 0.98 | 0.95 | 0.05 | asserted 0.96 |
| s3 | The computed gravitational radiation agrees with and extends the results of full numerical computations. | result 0.98 | 0.89 | 0.81 | asserted 1.00 |
What was examined, and what was not
- arXiv listing abstract v1
- full text
- figures and tables
- references and citing sentences
- relations to other papers
- P abstract
- S sections
- T body sentences
- C citations
- R cross-paper relations
Figures
Showing 1 of the paper's 3 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:gr-qc/9402039 by the authors.
References
How later papers used it
48 later papers cite it
2 later papers by other authors are listed below: 2 compared their own results with it.
Compares with it 2 of 4 papers with this label
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Solved an equation with two approaches, reproducing in both cases the literature results for head-on black hole collisions with the close limit approach.
Applications of the close-limit approximation: horizonless compact objects and scalar fields (2021) · 0.90 · paraphrased: the licence does not allow quoting
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Found that its total energy agrees with this paper's within one percent.
Challenging theories of gravitation: dark matter, compact objects and gravitational waves (2021) · 1.00 · paraphrased: the licence does not allow quoting
How the literature uses it
41 arXiv papers cite this in 72 sentences
Papers citing it · 48 sentences without a confident label
Builds on it 1 paper
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It is important to restress that we want to use the linearized approximation without necessarily restricting to the initial data being small perturbations of the AdS-Schwarzschild black brane, precisely in the spirit of the original close-limit approximation [ref] but now in the context of AdS spacetime.
Holographic isotropization linearized · Leading order correction to the pressure anisotropy · 0.86
Uses its method or tool 4 papers
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In order to model BBH configurations, we use results from the Close Limit Approximation (CLAP) of binary BHs [ref] .
CLAP for modified gravity: scalar instabilities in binary black hole spacetimes · Introduction · 1.00
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A possible way to circumvent the above problem is to use an alternative approach, in particular the close-limit approximation (CLAP) [ref] .
Applications of the close-limit approximation: horizonless compact objects and scalar fields · Introduction · 0.87
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The CLAP formalism of BBHs in GR succeeded to consistently describe such configurations [ref] , and we will use this approximation in what follows.
Challenging theories of gravitation: dark matter, compact objects and gravitational waves · Binary black hole background · 0.90
Compares with it 3 papers
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We have solved Eq. [ref] using two different approaches (see Appendix [ref] for details), reproducing in both cases the results in the literature for head-on BBH collisions with the CLAP approach [ref] .
Applications of the close-limit approximation: horizonless compact objects and scalar fields · Perturbations and their time evolution · 0.90
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The total energy obtained with our computation agrees with that of Ref. [ref] within one percent.
Challenging theories of gravitation: dark matter, compact objects and gravitational waves · Perturbations and their time evolution · 1.00
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* Using the Misner initial data [ref] as given by Price & Pullin [ref] , we reproduced in the case of head-on collision the waveform of their Fig. 2 and the associated radiated energy; cf. Eq. (16) in [ref] .
The Close-Limit Approximation for Black Hole Binaries with Post-Newtonian Initial Conditions · Numerical evolution · 0.93
Cites it as support 3 papers
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A second notable support to Simplicity and Universality is the Close-Limit approximation due to Pullin, Price, Gleiser, Khanna and collaborators [ref] .
Airy-function approach to binary black hole merger waveforms: The fold-caustic diffraction model · Asymptotic Reasoning and Structural Stability · 1.00
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Once a common horizon has formed, the geometry on a suitable Cauchy slice and in its future domain of dependence can be viewed as a perturbed remnant BH — a picture supported by the successes of the close-limit approximation [ref] , the Lazarus project [ref] , and the hybrid approach [ref] , which treat suitable post-merger regions perturbatively while retaining agreement with NR.
Foundations of Direct Waves in Schwarzschild Ringdown · Discussion · 0.96
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Additional motivation for the EOB treatment of the transition from plunge to ring-down came from work on the, so-called, “close limit approximation” [ref] .
The general relativistic two body problem · EOB description of the conservative dynamics of two body systems · 0.96
Cites it as background 6 papers
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0.5cm The Close limit approximation – The CLA was originally introduced in Ref. [ref] (see also Ref. [ref] for further analytical developments).
Nonlinearities of Schwarzschild Black Hole Head-on Collisions · Introduction · 0.83
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On the other hand, the close-limit approximation consists of an expansion in powers of the dimensionless ratio considered small[In the works [ref] , the CL parameter is defined as $c^2 r_12/ (G M)$.
The Close-Limit Approximation for Black Hole Binaries with Post-Newtonian Initial Conditions · Introduction · 0.87
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In the last stage the oscillation ceases with a power-law tail [ref] .
Black hole spectroscopy: prospects for testing the nature of black holes with gravitational wave observations · Black hole perturbation theory · 0.87
Discussion
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