Observing Signatures of Dynamical Space-Time through Gravitational Waves

Transcription

1 Observing Signatures of Dynamical Space-Time through Gravitational Waves Alessandra Buonanno for the LIGO Scientific Collaboration & Virgo Collaboration Max Planck Institute for Gravitational Physics (Albert Einstein Institute) Department of Physics, University of Maryland Black Holes, GWs & Spacetime Singularities, Vatican Observatory, Castel Gandolfo May 9-12, 2017

2 Outline Observation of gravitational waves by Advanced LIGO. The science from GW experiments stems on our ability to make precise predictions: theoretical groundwork to identify and interpret the signals. Astrophysics. Tests of general relativity in the strong-field, highly dynamical regime. Probing matter at supranuclear densities. Cosmology. The bright future of gravitational-wave astronomy comes with new theoretical challenges.

3 LIGO detections during O1: GW & GW (Abbott et al. PRL 116 (2016) ) (Abbott et al. PRL 116 (2016) ) Hanford Livingston GW150914: SNR=24 (very loud), 10 GW cycles, 0.2 sec. GW151226: SNR=13 (quieter), 55 GW cycles, 1.5 sec.

4 What LIGO detected: binary black-hole coalescences (Abbott et al. arxiv: ) GW150914: merger in detector s band, more massive binary GW151226: inspiral-plunge in detector s band, lower mass binary

5 Characteristics of binary black-hole coalescence Early inspiral: low velocity & weak gravitational field. (Abbott et al. PRL 116 (2016) ) Late inspiral/plunge: high velocity & strong gravitational field. Merger: nonlinear & non perturbative effects; rapidly varying gravitational field Ringdown: excitation of quasinormal modes/spacetime vibrations. Phase/amplitude evolution encodes unique information about the source Black holes of radius of 90 km at separation of 350 km are making 75 orbits per second before merging!

6 Waveform modeling to detect and infer source s properties 10 4 r c 2 /GM Post-Newtonian theory Effective one-body theory Perturbation rba theory gravitational selfforce Numerical Relativity (AB & Sathyaprakash 14) m 1 /m 2 Two parameters determine the range of validity of each method:

7 Post-Newtonian/post-Minkowskian formalism/effective field theory First developed in 1917 (Droste & Lorentz 1917, and Einstein, Infeld & Hoffmann 1938) (Blanchet, Damour, Iyer, Faye, AB, Bohe, Marsat; Jaranowski, Schaefer, Steinhoff; Will, Wiseman; Goldberger, Porto, Rothstein, Levi, Foffa, Sturani; Flanagan, Hinderer, Vines ) Small parameter is v/c or GM/rc m1 m2 m1 m2

8 Perturbation theory and gravitational self force (GSF) First works in 50-70s (Regge & Wheeler 56, Zerilli 70, Teukolsky 72) Small parameter is m 2/ m 1 Equation of gravitational perturbations in black-hole 2? + V`m = S`m m1 Green functions in Schwarzschild/Kerr spacetimes. (Fujita, Poisson, Sasaki, Shibata, Khanna, Hughes, Bernuzzi, Harms, ) m2 GSF: Accurate modeling of relativistic dynamics of large mass-ratio inspirals requires to include back-reaction effects due to interaction of small object with its own gravitational perturbation field. m1 m2 (Deitweiler, Whiting, Mino, Poisson, Quinn, Sasaki, Tanaka, Barack, Ori, Pound, van de Meent )

9 Numerical Relativity Breakthrough in 2005 (Pretorius 05, Campanelli et al. 06, Baker et al. 06) Kidder, Pfeiffer, Scheel, Lindblom, Szilagyi; Bruegmann, Hannam, Husa, Tichy; Laguna, Shoemaker; 4 y/m x/m Simulating extreme Spacetime (SXS) collaboration (Mroue et al. 13) Numerical-Relativity & Analytical Relativity collaboration (Hinder et al. 13)

10 The effective-one-body (EOB) approach EOB approach introduced before NR breakthrough AB, Pan, Taracchini, Barausse, Bohe, Shao, Hinderer, Steinhoff; Damour, Nagar, Bernuzzi, Bini, Balmelli; Iyer, Sathyaprakash; Jaranowski, Schaefer; PN Theory conservative dynamics and GW emission computed as a Taylor expansion Effective one body conservative dynamics and GW emission re written in summed and/or factorized form Numerical relativity two body dynamics and GW emission computed with all non linearities EOB model uses best information available in PN theory, but resums PN terms in suitable way to describe accurately dynamics and radiation during inspiral and plunge. EOB assumes comparable-mass description is smooth deformation of testparticle limit. It employs non-perturbative ingredients and models analytically merger-ringdown signal.

11 The effective-one-body approach in a nutshell Real description m 2 Effective description! Two-body dynamics is mapped into dynamics of one-effective body moving in deformed blackhole spacetime, deformation being the mass ratio. Some key ideas of EOB model were inspired by quantum field theory when describing energy of comparable-mass charged bodies. E real m 1 g!ν m m 1 2 Map E eff g eff!ν J real N J real eff (AB & Damour PRD59 (1999) ) N eff

12 EOB inspiral-merger-ringdown analytic waveform (credit: Hinderer) "!" #$ #" $ " # $%& ν!"!#$% gravitational waveform inspiral-plunge merger-ringdown $ #" #$!"!" #$ #" $ " $ #" #$!"! frequency: GM!/c x orbital freq inspiral-plunge GW freq merger-ringdown GW freq c 3 t/gm (AB & Damour PRD62 (2000) )

13 On the simplicity of merger signal equation of gravitational perturbations in black-hole spacetime (Regge & Wheeler 56, Zerilli 70, Teukolsky 2? + V`m = S`m black hole horizon light ring Peak of black-hole potential close to light ring. Once particle is inside potential, direct gravitational radiation from its motion is strongly filtered by potential barrier (high-pass filter). Only black-hole spacetime vibrations (quasi-normal modes) leaks out black-hole potential.

14 Waveforms combining analytical & numerical relativity Effective-one-body (EOB) formalism PN Theory conservative dynamics and GW emission computed as a Taylor expansion Effective one body conservative dynamics and GW emission re written in summed and/or factorized form Numerical relativity two body dynamics and GW emission computed with all non linearities χ NR nonspinning NR spinning test-particle limit ν 38 SXS simulations gravitational waveform mass ratio = 1 and spins S /m 2 1 = 0.98, S 2 /m2 2 = (Taracchini, AB, Pan, Hinderer & SXS 14, Puerrer 15) NR EOBNR t/m Inspiral-merger-ringdown phenomenological waveforms fitting EOB & NR (IMRPhenom) (Khan et al. 16, Hannam et al 16)

15 Detection confidence with modeled search in O1 Matched filtering employed 1,2 < GW GW LVT (gstlal) LVT (PyCBC) GW templates 200,000 EOBNR templates m1 [M ] 102 >5 4 5 >5 Search Result Search Background Background excluding GW GW ,000 PN Number of events m2 [M ] 1 < , 2 < ,2 < 0.05 (Abbott et al. arxiv: ) GW Detection statistic ˆc 22 Confidence (FAP) > 5.3 (< 2x10-7) that GW & GW were real gravitational-wave signals. Minimal-assumption search reached high detection confidence (> 4.6 ) only for GW

16 Numerical-relativity simulation of a binary black-hole merger with parameters close to GW (visualization credit: AEI) (Ossokine, AB & SXS project) NR EOBNR 0.2 Re[rh 22 /M] 0 0 (Ossokine, AB & SXS project) Hz for M = 70 Msun 30 Hz for M = 70 Msun t-t peak (M) t-t peak (M) Waveform models very closely match the exact solution from Einstein equations around GW & GW Systematics due to modeling are smaller than statistical errors. (see also Abbott et al. arxiv: )

17 Numerical-relativity simulation of a binary black-hole merger with parameters close to GW (visualization credit: Dietrich, (Ossokine, AB & SXS project) (Abbott et al. PRL 116 (2016) ) Systematics due to modeling are smaller than statistical errors.

18 Unveiling binary black holes properties: masses (Abbott et al. PRX 6 (2016) ) GW m source 2 apple m source 1 GW (Abbott et al. PRL 116 (2016) ) We measure best the chirp mass GW150914: merger in band, total mass well measured, good measurement of individual masses. M = M 3/5 GW151226: merger outside band, individual masses measured less precisely.

19 GW GW BHs spins not maximal, and for GW one BH s spin larger than 0.2 at 99% confidence. Spin of primary BH < 0.7. No information about precession. (Abbott et al. PRL 116 (2016) ) (Abbott et al. PRX 6 (2016) ) Unveiling binary black-holes properties: spins

20 Implications for binary formation scenarios BHs observed heavier than expected for GW How did they form? Dynamical capture or massive binary stars undergoing core-collapse or chemically homogeneous stars or primordial BHs or PopIII stars or binaries in AGN disks? weak wind (Abbott et al. ApJ L22 (2016) 818) (Lipunov et al 97, Belczynski et al. 10, Dominik et al. 15, Belczynski et al. 15, Nelemans et al. 01, Rodriguez et al. 16, de Mink et al. 09, Marchant et al. 16, Mckernan et al. 16, Bird et al. 16, de Mink & Mandel 16, Belczynski et al. 16, ) (Heger et al. 03, Mapelli et al. 09, Belczynski et al. 10, Mapelli et al. 13, Spera et al. 15)

21 Tests of GR with LIGO s sources Given current tight constraints on GR (e.g., Solar system, binary pulsars), can any GR deviation be observed with LIGO? Newton Binary Pulsars highly-dynamical Gravitational Waves Solar System v/c (credit: Sennett) strong-field

22 Tests of GR with first LIGO s black holes: inspiral GW150914/GW s rapidly varying orbital periods allow us to bound higher-order PN coefficients in gravitational phase. (Abbott et al. arxiv: ) 10 1 GW GW GW GW (Arun et al. 06, Mishra et al. 10, Yunes & Pretorius 09, Li et al. 12) ˆ' 10 0 PN parameters describe: tails of radiation due to backscattering, spin-orbit and spin-spin couplings PN 0.5PN 1PN 1.5PN 2PN 2.5PN 3PN 3.5PN PN order First GR test in the genuinely dynamical, strong-field regime.

23 Could we prove that GW s remnant is a BH? QNM decay time (ms) IMR (l = 2,m = 2,n = 0) 1.0 ms 7.0 ms 3.0 ms 5.0 ms 7.0 ms QNM frequency (Hz) (Abbott et al. PRL 116 (2016) ) We measured frequency & decay time of damped sinusoid in the data after GW s peak. Multiple QNMs need to be measured to extract mass and spin of remnant, test no-hair theorem and second-law black-hole mechanics (Israel 69, Carter 71; Hawking 71, Bardeen 73).

24 Can we probe BH horizon from GW ringdown? What determines ringdown signal? Light ring or horizon? QNM spectrum differs in BH and horizonless object. horizonless object (Cardoso, Franzin & Pani 16) black hole Ringdown and QNM signals can be different in horizonless objects. GW echoes! (Cardoso et al. 16) same ringdown t radial infall signal different QNM signals

25 Inference of cosmological parameters in future LIGO searches Wide-field galaxy surveys can provide (sky positions and) redshifts (Schutz 1986) single GW event multiple events 3 detectors GW catalogue consists of 1,000 events sampled from SDSS at z apple detectors (Del Pozzo 12) Measurement of Hubble constant H 0 with accuracy of 5% at 95% confidence after GW observations with 3 detectors.

26 Upper limits on rates of neutron star mergers Dominik et al. pop syn O3 O2 O1 (Abbott et al. arxiv: ) de Mink & Belczynski pop syn Vangioni et al. r-process Jin et al. kilonova Petrillo et al. confidence: NSNS rate < 12,600/(Gpc) 3 /yr Coward et al. GRB Siellez et al. GRB NSBH rate < 3,600/(Gpc) 3 /yr Fong et al. GRB Kim et al. pulsar aligo 2010 rate compendium O3 O2 O BNS Rate (Gpc 3 yr 1 ) Dominik et al. pop syn de Mink & Belczynski pop syn Assuming GRB rate of 3-30/(Gpc) 3 /yr and all GRBs have NSNS (NSBH) progenitors, beaming angle > ( ) deg. Vangioni et al. r-process Jin et al. kilonova Petrillo et al. GRB Coward et al. GRB Fong et al. GRB Observed GRB beaming angles 3-25 deg aligo 2010 rate compendium NSBH Rate (Gpc 3 yr 1 )

27 Probing NS s equation of state with LIGO and Virgo NSs are unique laboratories to study baryonic matter at supra-nuclear density (Baade & Zwicky 1934, Gamow 1937, Landau 1938, Oppenheimer & Volkoff 1939, Cameron 1959, Wheeler 1966) NS s characteristics: - mass: 1-3 Msun - radius: 9-15 km - core density > 1014 g/cm3 (credit: Hinderer) (credit: Read)!"!$! 'ff' *$+,'!"!$$ -.%! "+/$ 3-0!1 2 1/ / 3 1,1-2. /+0 ($+*- '!"!$& 456/, :;85/6-!"#!"!"!$%!"#$% &'()'( 910, -,<:2;.810 -, = ;; 84; 08!"!$# <::7> <? =; 8!" #"!"" $+21*+!*+,-+ (. -%'ff *(!*( '*$# '!()" #""!""" #""" (Antoniadis et al. 16)

28 With several tens of events, possible to distinguish some EOS The influence of NS s internal structure on waveform is characterized by a single (constant) parameter, the tidal deformability measures star s quadrupole deformation in response to the companion perturbing tidal field: (Kochanek 92, Bildsten & Cutler 92, Lai et al. 93, Lai 94) (Agathos et al. 15, Del Pozzo et al. 13 (see also Lackey et al. 14; Lynch et al. 14; Yagi et al. 15))

29 Waveform modeling for NS-NS binaries up to merger mass ratio = 1.5, EOS = MS1b (Dietrich & Hinderer 17) time tidal EOB waveform versus NR waveform Results extended to NS-BHs (Damour & Nagar 12; Bernuzzi et al. 15; Hinderer et al. 16, Steinhoff et al. 16)

30 Advanced detectors roadmap and rates Strain noise amplitude/hz 1= (Aasi et al. arxiv: ) Advanced LIGO Early (2015 { 16, 40 { 80 Mpc) Mid (2016 { 17, 80 { 120 Mpc) Late (2017 { 18, 120 { 170 Mpc) Design (2019, 200 Mpc) BNS-optimized (215 Mpc) Frequency/Hz Detection design sensitivity: Binary neutron stars: per year Binary black holes: tens to hundreds per year! P (N >{10, 35, 70} {xj}, hvti) 100% 80% 60% 40% 20% 0% Rates: /(Gpc) 3 /yr O hvti 0 /hvti O1 O3 (Abbott et al. arxiv: )

31 The new era of precision gravitational-wave astrophysics We can now probe the most extreme astrophysical objects in the universe, and learn how they formed. We can now learn about gravity in the genuinely highly dynamical, strong field regime. We can now unveil properties of neutron stars unaccessible in other ways. We can now provide the most convincing evidence that compact objects in our Universe are black holes as predicted in GR. To take full advantage of discovery potential in next years and decades we need to make precise theoretical predictions.