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Measuring gravitational waves from binary black hole coalescences: I. Signal to noise for inspiral, merger, and ringdown

General Relativity and Quantum Cosmology · Submitted 16 Jan 1997 · 103 references

Pith's verdict: A foundational, largely honest SNR survey whose headline mass thresholds are softer than the confident framing suggests.

T0 · AI review

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arXiv IDgr-qc/9701039 (version 2)
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CitationEanna E. Flanagan, Scott A. Hughes. "Measuring gravitational waves from binary black hole coalescences: I. Signal to noise for inspiral, merger, and ringdown." arXiv:gr-qc/9701039 (1997). https://pith.science/paper/AK2LQIOZ
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Referee report
The paper

The paper claims

For heavy black holes, the merger outshouts the chirp

The reading

Flanagan and Hughes ask a practical question about detectors that had not yet taken data: for a binary black hole of a given total mass, which portion of the gravitational-wave signal should a search actually be built around? Their answer is that no single answer exists. The adiabatic inspiral chirp, the violent merger, and the ringdown of the final black hole each dominate the signal-to-noise ratio in a different mass band, so a search tuned only to inspiral waves would silently lose the heavy end of the population. The calculation is a matched-filter signal-to-noise ratio averaged over source orientation and sky position, written as an integral of the source's emitted energy spectrum against the detector's noise curve, then evaluated with fitted noise models for initial LIGO, advanced LIGO, and LISA. If the estimates hold, coalescing black holes would be visible much farther out than the neutron-star binaries then treated as the primary target, and ringdown and merger searches become a requirement rather than an optional extra.

What carries the argument

The load-bearing object is the angle-averaged matched-filter signal-to-noise identity, Eq. (2.34): $4$-normalized optimal filtering squared, averaged over source orientation and position, equals a frequency integral of the source's emitted energy spectrum $dE_e/df_e$ evaluated at the redshifted frequency $(1+z)f$, weighted by $1/(f^2 S_h(f))$ and scaled by $(1+z)^2/D(z)^2$. Its virtue is that the answer depends only on the energy spectrum, not on the detailed waveform or the geometry of the source relative to the detector, so the three phases can be compared on a single footing. Feeding in three model spectra — the Newtonian quadrupole inspiral spectrum cut off at $f=0.02/M$, a flat merger spectrum from $0.02/M$ to $0.13/M$ carrying 10 percent of the mass-energy, and a Breit-Wigner ringdown resonance at the $l=m=2$ quasinormal frequency with 3 percent of the mass-energy — against piecewise power-law fits to the detector noise curves produces the mass-dependent signal-to-noise curves that drive every conclusion. A second piece of machinery is the template-counting metric on the two-dimensional ringdown parameter space of frequency and quality factor, which yields the estimate of roughly 6000 templates for a 10 percent event-rate loss.

Extended reading notes

Core claim

The paper establishes a mass-dependent rule for how binary black hole coalescences should be searched for. Using an angle-averaged optimal-filtering signal-to-noise ratio, it shows that the inspiral phase dominates only for relatively light systems, while the merger and ringdown phases take over above roughly $(1+z)M$ of about $30M_*$ for the initial interferometers and about $60M_*$ for the advanced ones, with the inspiral contribution cutting off entirely near $100M_*$ and $410M_*$ respectively once its whole spectrum falls below the seismic wall. The authors then turn that into concrete reach estimates: a matched-filter ringdown search needs only about 6000 templates or fewer and should find equal-mass systems of roughly $100$ to $700M_*$ out to about 200 Mpc with initial interferometers, $200$ to $3000M_*$ out to $z$ near 1 with advanced ones, and $10^6$ to $3$ times $10^8M_*$ out to $z$ beyond 100 with LISA. Finally, they argue that a nonlinear noise-monitoring search for merger waves, which needs no detailed waveform knowledge, could raise the number of detected massive binaries by a factor of order ten, with a complete set of numerical-relativity merger templates adding at most another factor of about four.

Load-bearing premise

The merger signal-to-noise numbers, and the headline factor-of-ten gain from merger searches, rest on a chosen flat merger energy spectrum carrying 10 percent of the total mass-energy, a value the authors themselves describe as a reasonable upper bound achievable in favorable cases rather than a best guess.

Editorial extensions

If this is right

  • A search pipeline built exclusively around the inspiral chirp will systematically miss equal-mass binaries above roughly 30 solar masses for initial interferometers and 60 for advanced ones, because their signal-to-noise is carried by the merger and ringdown instead.
  • Ringdown searches are practical now rather than in some future: the template bank is small compared with inspiral banks, and the waveform family is known analytically from Kerr perturbation theory.
  • Coalescing black holes, not neutron-star binaries, may be the first gravitational-wave sources detected, because their larger mass buys a distance gain that plausibly outweighs a lower event rate.
  • Even without any merger waveform templates, a nonlinear noise-monitoring statistic can recover a large share of the massive binaries that template searches would miss, so the unknown merger waveform is not a hard barrier to detection.
  • LISA would measure supermassive black hole coalescences with signal-to-noise of order $10^4$, high enough that the merger and ringdown phases are visible essentially throughout the observable universe.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The mass-dependent search-phase rule is a statement about where the signal-to-noise lives, not about where the physics is best understood; it implies a trade between detection reach and interpretability that later observing strategy has to make explicitly.
  • Because the ringdown frequency and damping time map one-to-one onto final mass and spin, a ringdown detection is simultaneously a measurement of the remnant, so the ringdown search doubles as a black-hole census instrument rather than only a trigger.
  • The paper's own logic suggests the reverse search problem is worth stating: given a detected ringdown with no inspiral counterpart, the absence of inspiral signal above the seismic cutoff itself constrains the total mass, which is a consistency check that needs no merger templates.
  • The noise-monitoring statistic is essentially an incoherent power sum over frequency bins, so its advantage shrinks as the number of independent bins grows; this predicts that any future waveform family richer than the merger's roughly 10 to 60 bins would erode the factor-of-ten gain claimed here.
Original abstract

We estimate the expected signal-to-noise ratios (SNRs) from the three phases (inspiral,merger,ringdown) of coalescing binary black holes (BBHs) for initial and advanced ground-based interferometers (LIGO/VIRGO) and for space-based interferometers (LISA). LIGO/VIRGO can do moderate SNR (a few tens), moderate accuracy studies of BBH coalescences in the mass range of a few to about 2000 solar masses; LISA can do high SNR (of order 10^4) high accuracy studies in the mass range of about 10^5 to 10^8 solar masses. BBHs might well be the first sources detected by LIGO/VIRGO: they are visible to much larger distances (up to 500 Mpc by initial interferometers) than coalescing neutron star binaries (heretofore regarded as the "bread and butter" workhorse source for LIGO/VIRGO, visible to about 30 Mpc by initial interferometers). Low-mass BBHs (up to 50 solar masses for initial LIGO interferometers; 100 for advanced; 10^6 for LISA) are best searched for via their well-understood inspiral waves; higher mass BBHs must be searched for via their poorly understood merger waves and/or their well-understood ringdown waves. A matched filtering search for massive BBHs based on ringdown waves should be capable of finding BBHs in the mass range of about 100 to 700 solar masses out to 200 Mpc (initial LIGO interferometers), and 200 to 3000 solar masses out to about z=1 (advanced interferometers). The required number of templates is of order 6000 or less. Searches based on merger waves could increase the number of detected massive BBHs by a factor of order 10 or more over those found from inspiral and ringdown waves, without detailed knowledge of the waveform shapes, using a "noise monitoring" search algorithm. A full set of merger templates from numerical relativity could further increase the number of detected BBHs by an additional factor of up to 4.

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.

Compiled by classifier-1.13-20260917 via OpenRouter, question bank abstract-p1-20260923, 2026-09-23: 1 request, 7,020 input tokens, $0.0003 reported.

What the abstract itself states, as probabilities: claims first 0.07 · states limitation 0.53 · human participants 0.01 · controlled comparison 0.12 · randomized assignment 0.01 · states quantitative result 0.98 · compares with prior results 0.80 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v2. Results and the main claim are underlined; .

We estimate the expected signal-to-noise ratios (SNRs) from the three phases (inspiral,merger,ringdown) of coalescing binary black holes (BBHs) for initial and advanced ground-based interferometers (LIGO/VIRGO) and for space-based interferometers (LISA). LIGO/VIRGO can do moderate SNR (a few tens), moderate accuracy studies of BBH coalescences in the mass range of a few to about 2000 solar masses; LISA can do high SNR (of order 10^4) high accuracy studies in the mass range of about 10^5 to 10^8 solar masses. BBHs might well be the first sources detected by LIGO/VIRGO: they are visible to much larger distances (up to 500 Mpc by initial interferometers) than coalescing neutron star binaries (heretofore regarded as the "bread and butter" workhorse source for LIGO/VIRGO, visible to about 30 Mpc by initial interferometers). Low-mass BBHs (up to 50 solar masses for initial LIGO interferometers; 100 for advanced; 10^6 for LISA) are best searched for via their well-understood inspiral waves; higher mass BBHs must be searched for via their poorly understood merger waves and/or their well-understood ringdown waves. A matched filtering search for massive BBHs based on ringdown waves should be capable of finding BBHs in the mass range of about 100 to 700 solar masses out to 200 Mpc (initial LIGO interferometers), and 200 to 3000 solar masses out to about z=1 (advanced interferometers). The required number of templates is of order 6000 or less. Searches based on merger waves could increase the number of detected massive BBHs by a factor of order 10 or more over those found from inspiral and ringdown waves, without detailed knowledge of the waveform shapes, using a "noise monitoring" search algorithm. A full set of merger templates from numerical relativity could further increase the number of detected BBHs by an additional factor of up to 4.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 We estimate the expected signal-to-noise ratios (SNRs) from the three phases (inspiral,merger,ringdown) of coalescing binary black holes (BBHs) for initial and advanced ground-based interferometers (LIGO/VIRGO) and for space-based interferometers (LISA). contribution 1.00 0.89 0.13 asserted 0.91
s1 LIGO/VIRGO can do moderate SNR (a few tens), moderate accuracy studies of BBH coalescences in the mass range of a few to about 2000 solar masses; LISA can do high SNR (of order 10^4) high accuracy studies in the mass range of about 10^5 to 10^8 solar masses. result 0.95 0.72 0.32 asserted 0.88
s2 BBHs might well be the first sources detected by LIGO/VIRGO: they are visible to much larger distances (up to 500 Mpc by initial interferometers) than coalescing neutron star binaries (heretofore regarded as the "bread and butter" workhorse source for LIGO/VIRGO, visible to about 30 Mpc by initial interferometers). result 0.49 0.28 0.11 hedged possibility 0.49
s3 Low-mass BBHs (up to 50 solar masses for initial LIGO interferometers; 100 for advanced; 10^6 for LISA) are best searched for via their well-understood inspiral waves; higher mass BBHs must be searched for via their poorly understood merger waves and/or their well-understood ringdown waves. result 0.70 0.54 0.11 asserted 0.95
s4 A matched filtering search for massive BBHs based on ringdown waves should be capable of finding BBHs in the mass range of about 100 to 700 solar masses out to 200 Mpc (initial LIGO interferometers), and 200 to 3000 solar masses out to about z=1 (advanced interferometers). result 0.99 0.67 0.13 hedged possibility 0.95
s5 The required number of templates is of order 6000 or less. result 0.96 0.74 0.07 asserted 0.99
s6 Searches based on merger waves could increase the number of detected massive BBHs by a factor of order 10 or more over those found from inspiral and ringdown waves, without detailed knowledge of the waveform shapes, using a "noise monitoring" search algorithm. result 0.88 0.42 0.15 hedged possibility 0.99
s7 A full set of merger templates from numerical relativity could further increase the number of detected BBHs by an additional factor of up to 4. result 0.60 0.35 0.10 hedged possibility 0.94

What kind of paper the classifier reports this is: theoretical result 0.76 · evidence from simulation or computation 0.71.

What was examined, and what was not

sources read
  • arXiv listing abstract v2
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures
Figure 1. FIG. 1. An illustration of the relative magnitudes of our
Figure 2. FIG. 2. A merger of a binary consisting of two 50
Figure 3. [10] K. S. Thorne, in Proceedings of the Snowmass 95 Summer Study on Particle and Nuclear Astrophysics, eds. E.W. Kolb and R. Peccei (World Scientific, Singapore, 1995) (gr-qc/9506086). [11] A. Ori and K. S. Thorne, in preparation. [12] D. Lai and A. G. Wiseman, “Innermost Stable Circular Orbit of Inspiraling Neutron-Star Binaries: Tidal Effects, Post-Newtonian Effects and the Neutron-Star Equation of State”, gr-qc/9609014. [13] S. A. Teukolsky and W. H. Press, Astrophys. J. 193, 443 (1974). [14] S. Chandrasekhar and S. L. Detweiler, Proc. R. Soc. Lon￾don A344, 441 (1975). [15] F.…
Figure 4. FIG. 4. The signal to noise ratio (SNR) for equal-mass
Figure 5. FIG. 5. The SNR values for advanced LIGO interferome
Figure 6. FIG. 6. The signal to noise ratio (SNR) for equal-mass
Figure 7. FIG. 7. This plot shows that factor by which the event

Figures reproduced from arXiv:gr-qc/9701039 by the authors.

References
How later papers used it

134 later papers cite it

Evidence: substantial. 133 of the citing papers share no author with it, and 56 of those carry a confident label from Pith's citation classifier.

Pith read 19 of the 189 citing sentences, choosing only those whose citation markers point at this paper alone, and wrote the paraphrases from them. The summary, the counts, the evidence level, the links and the quotes come from code; the summary counts the papers listed below. A later paper is listed under a label when Pith's citation classifier gives one of its sentences that label at probability 0.8 or more (0.95 for support), Pith's reading finds that the citing paper itself did it, and a second check confirms the paraphrase against the sentence. This section lists uses only. It does not list criticism or disagreement, so their absence here says nothing about how the paper has been received. Papers that share an author with this one are listed apart, under "By the same authors". A quote is the citing authors' own sentence, shown when their paper's licence is CC BY, CC BY-SA or CC0. JSON

Uses its method or tool 8 of 52 papers with this label
How the literature uses it

77 arXiv papers cite this in 111 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers citing it · 59 sentences without a confident label

Contests it 1 paper
  • This is essentially the approach followed by Thorne [ref] , who examined the Christodoulou memory from unmodeled GW bursts from merging BHs.[Note that Thorne's [ref] normalization of the SNR should be corrected by multiplying his Eq. (A1) by $√(2)$ (see footnote 61 of Ref. [ref] ).] However the ZFL is inadequate for computing the memory's SNR for some sources.

    Post-Newtonian corrections to the gravitational-wave memory for quasicircular, inspiralling compact binaries · Detecting memory with gravitational-wave interferometers · contest 0.77

Uses its method or tool 29 papers
Uses its data or values 3 papers
Cites it as background 12 papers
  • The QNM amplitudes $A_ℓm n$ and phases $ϕ_ℓm n$ were unknown before the first numerical BH merger simulations, and early work on BH spectroscopy [ref] had to rely on educated guesses [ref] .

    Analysis of Ringdown Overtones in GW150914 · Introduction · 0.90

  • The inspiral waveform measured in a gravitational wave detector is of the form of [ref] h(t) = h_0(t) cosϕ(t), where h_0(t)=4 Q/D_L G Mη Ω^2 r^2 and ϕ(t) = ∫2πf dt, with $D_L$ being the luminosity distance to the source and where $Q$ encodes the detector response as a function of the angular position and orientation of the binary.

    Prospects for axion searches with Advanced LIGO through binary mergers · Waveform · 0.84

  • With the emergence of GW astronomy, we now know that low-mass IMBH can form and grow through mergers with other BH[The term IMBH first began to appear in published papers from the late 1990s that were predicting the type of merging BH that could potentially be observed with future GW missions [ref] .]

    Intermediate-Mass Black Holes in Star Clusters and Dwarf Galaxies · Context and definition · 0.87

Discussion

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