Gravitational wave observations of binary black hole mergers Miami 2017

James A. Clark December 15, 2017 The story so far. . .

In two observing runs (“O1”, “O2”) we have so observed: O1: GW150914, LVT1510121, GW151226 • O2: GW170104, GW170608, GW170814 •

1 “LVT”: LIGO-Virgo transient, lower significance 1 / 21 Masses

GW150914: spectacular discovery of unknown class of black hole, subsequent measurements probing black hole mass distribution →

2 / 21 A New Population of Black Holes

3 / 21 Overview

This talk: an introduction to gravitational wave (GW) observations of binary black hole (BBH) mergers

1 BBH Observations GW150914 GW151226 GW170104 GW170608 GW170814 2 Astrophysical Implications Progenitor Systems Image: butterfly1

4 / 21 BBH Observations GW150914

On September 14, 2015. . . first detection at > 5σ (FAR< 10−7 yr−1)

SNR=24, (m1, m2) = (36, 29) M , D ∼ 410 Mpc [1] 5 / 21 Inferring Source Properties

Binary parameter space:

Component masses: m1, m2 • 2 3 = 6 spin components • × Binary orientation: θJN , φc, ψ • Sky-location & distance: (α, δ)& • D 15-dimensional waveform model!

Inspiral phase evolution accurately modeled via post-Newtonian theory: Leading-order amplitude and phase evolution: chirp mass [2]: • (m m )3/5 = 1 2 c 1/5 M (m1 + m2)

Additional parameters (q = m2/m1 1), effective spin χeff enter at • ≤ higher PN-order Effective spin – most important combination of spins for evolution of • inspiral [3]: 6 / 21   c ~χ1 ~χ1 χeff = + Lˆ GM m1 m2 · Inferring Source Properties

Source properties (generally) determined from Bayesian analysis of a given waveform model:

Time series data output from detector, given a signal h(t), noise • n(t): d(t) = h(t) + n(t) Signal h(t) is a linear combination of polarizations, weighted by • antenna beam patterns F+,×: ~ ~ h(t) = F+(α, δ, ψ)h+(t; θ) + F×(α, δ, ψ)h×(t; θ) ~ Source properties θ = c , q, χeff , , θJN , φc,... • {M D } Information about source properties θ~ is determined from posterior probability density function:

p(θ~ d~) p(θ~) (d~ θ~) | ∼ L | Assumes signal model faithfully models the underlying signal! 7 / 21 GW150914: Masses

⇒

Component mass distributions [4] Final mass & spin [4]

• Fitting formula from numerical relativity (NR) for final mass, spin +4.5±0.8 +4.1±0.7 • Initial Mtot = 65.0−4.0±0.7 M , Final Mtot = 62.0−3.7±0.6 M 2 • Erad ∼ 3 M c : peak luminosity >> than entire electromagnetic (EM)-observable Universe!

8 / 21 GW150914: Cross-validation

Two approaches to waveform reconstruction:

1. h(t) = h(t; c , q, χeff , , θJN , φc,... ) M D 2. h(t) = wavelet decomposition dictated by coherent network signal Excellent agreement validation of BBH waveform models [4, 5] → 9 / 21 GW151226

SNR=13, (m1, m2) = (14.2, 7.5) M , D ∼ 440 Mpc [6] 10 / 21 GW151226 Source Properties: spin configuration

Figure 1: Component spin magnitudes & Mass-weighted spin χ and in-plane eff orientations spin-components χp [6] • Lower mass → merger at higher frequency, longer inspiral • Longer inspiral → more informative spin measurement

• p(χeff > 0|D) > 99% → at least 1 BH has non-zero spin

11 / 21 GW150914, LVT151012 & GW151226: durations & spins

12 / 21 GW170104

More distant cousin of GW150914:

SNR=13, (m1, m2) = (31.2, 19.4) M , D ∼ 880 Mpc [7]

Waveform reconstructions remain consistent

p(χeff < 0|D) = 0.82 → large total spin aligned with orbital angular

momentum is disfavored 13 / 21 GW170608

Most recent result, lightest BBH so far!

SNR=13, (m1, m2) = (12, 7) M , D ∼ 340 Mpc [8] Potential selection bias → systems with

uninformative precession (χp) Spin inferences for GW170608 [8] measurements 14 / 21 GW170814

First Virgo observation, first triple-detector detection! [9]

Hanford Livingston Virgo 14 12 10 8

SNR 6 4 2 0 5.0 4.5 256 4.0 3.5 128 3.0 2.5 64 2.0 1.5

Frequency [Hz] 32 1.0 0.5 Normalized Amplitude 16 0.0

] 1.0

-21 2 5 5 0.5

0.0 0 0 0 noise σ 0.5 − 5 5 − 2 − −

Whitened Strain [10 1.0 − 0.46 0.48 0.50 0.52 0.54 0.56 0.46 0.48 0.50 0.52 0.54 0.56 0.46 0.48 0.50 0.52 0.54 0.56 Time [s] Time [s] Time [s]

SNR=18, (m1, m2) = (30.5, 25.3) M , D ∼ 540 Mpc [9] 15 / 21 GW170814: Sky localization

Triple-coincident observations sky localization → • 1 GW detector: omni-directional but non-uniform • 2 GW detectors: time-delay constrains source to annulus + amplitude ratio constraints • 3 GW detectors: intersection of 2 annuli → sky-patches

Geometry of HLV network and signal travel times [10]

• Initial HL rapid localization: 1160 deg2 • Rapid localization +Virgo: 100 deg2

2 Localization of GW170814 [9] • Full parameter estimation: 60 deg 16 / 21 Observation Summary: Sky localization

90% credible sky-areas

GW150914: 230 deg2 [11] LVT151012: 1600 deg2 [11] GW151226: 850 deg2 [11] GW170104: 1200 deg2 [7] GW170814: 50 deg2 [9]

17 / 21 Astrophysical Implications Massive BH Progenitor Systems

GW150914: m1, m2 > all • known BH masses BH formation: • 1. Supernova + fall-back 2. Failed SN + prompt collapse Key factor: stellar wind • metallicity Z: Figure 2: Dependence of maximum BH mass on Low Z → lower opacity, metallicity [12] (Bands: GW150914 m1, m2) weaker winds & less mass-loss Conclusion: GW150914 BBH formed in a low-metallicity environment

18 / 21 Constraining Binary Evolution Scenarios

BBH formation channels (see e.g., [11]): 1. dense stellar environment dynamical formation  → 2. isolated binary evolution with a common envelope phase  3. chemically homogeneous evolution, tidally-locked binaries  Expect large, aligned spins: implausible in light of GW170104

Dynamical BBH formation [13] BBH through isolated evolution [14] 19 / 21 Summary

GW BBH observations • becoming “routine” (!) GWs encode source parameters • Some parameters measured well (e.g., chirp mass) Others much harder (e.g., mass ratio, spin orientations) GW observations starting to • probe black hole formation & evolution

Expected BBH detection rates from O1 [11] Just scraping the surface:

• Whole suites of tests of general relativity! • Higher-order multipoles + precession in waveform models • Direct comparisons with numerical relativity

• Searches for “intermediate” mass BBH (> 100 M ) 20 / 21 Observation Summary: Spins & Masses

Watch this space!

21 / 21 O1 Source Parameters

Figure 3: Trigger characteristics and source parameters for the O1 BBH triplet [11] GW170104

Figure 4: Trigger characteristics and source parameters for GW170104 [7] GW170608, GW170814

Figure 6: Trigger characteristics and source Figure 5: Trigger characteristics and source parameters for GW170814 [9] parameters for GW170608 [8] References

[1] B. P. Abbott et al. [Virgo and LIGO Scientific Collaborations], , “Observation of Gravitational Waves from a Binary Black Hole Merger”, Phys. Rev. Lett. 116, 061102 (2016), arXiv:1602.03837 [2] B. S. Sathyaprakash & B. F. Schutz, “Physics, Astrophysics and Cosmology with Gravitational Waves”, Living Rev. Relativ. (2009) [3] P. Ajith et al, “Inspiral-Merger-Ringdown Waveforms for Black-Hole Binaries with Nonprecessing Spins” Phys. Rev. Lett. 106, 241101 (2011) [4] B. P. Abbott et al. [Virgo and LIGO Scientific Collaborations], , “Properties of the binary black hole merger GW150914”, Phys. Rev. Lett. 116, 241102 (2016), arXiv:1602.03840 References

[5] B. P. Abbott et al. [Virgo and LIGO Scientific Collaborations], “Tests of general relativity with GW150914”, Phys. Rev. Lett. 116, 221101 (2016), arXiv:1602.03841 [6] B. P. Abbott et al. [Virgo and LIGO Scientific Collaborations], , “GW151226: Observation of Gravitational Waves from a 22-Solar-Mass Binary Black Hole Coalescence”, Phys. Rev. Lett. 16 241103 (2016) arXiv:1606.04855 [7] B. P. Abbott et al. [Virgo and LIGO Scientific Collaborations], “GW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2”, Phys. Rev. Lett. 118, 221101 (2017) [8] B. P. Abbott et al. [Virgo and LIGO Scientific Collaborations], “GW170608: Observation of a 19-solar-mass Binary Black Hole Coalescence”, Submitted to Astrophys. J. Lett (2017), arxiv:1711.05578 References

[9] B. P. Abbott et al. [Virgo and LIGO Scientific Collaborations], “GW170814: A Three-Detector Observation of Gravitational Waves from a Binary Black Hole Coalescence”, Phys. Rev. Lett. 119, 141101 (2017), arxiv:1709.09660 [10] S. Chatterji et al., “Coherent network analysis technique for discriminating gravitational-wave bursts from instrumental noise”, Phys. Rev. D 74, 082005 (2006) [11] B. P. Abbott et al. [Virgo and LIGO Scientific Collaborations], , “Binary Black Hole Mergers in the first Advanced LIGO Observing Run”, Phys. Rev. X 6, 041015 (2016), arXiv:1606.04856 [12] B. P. Abbott et al. [Virgo and LIGO Scientific Collaborations], , “Astrophysical Implications of the Binary Black-Hole Merger GW150914”, Astrophys. J. Lett., 818, L22, (2016), arXiv:1602.03846 References

[13] C. Rodriguez, et al., “Dynamical Formattion of the GW150914 Binary Black Hole”, Astrophys. J. Lett. 824 1 (2016) [14] K. Belczynski et al., “The first gravitational-wave source from the isolated evolution of two stars in the 40100 solar mass range”, Nature 534, 512–515 (2016)