Studying Fundamental Physics Using Current and Future Gravitational-Wave Detectors
Martin Hendry Institute for Gravitational Research SUPA School of Physics & Astronomy University of Glasgow, UK Gravitational Waves: the Story So Far
In General Relativity gravity is described by the curvature of space-time
◼Matter tells spacetime how to curve. ◼Spacetime tells matter how to move
Gravitational waves are ripples in spacetime propagating at the speed of light (according to GR)
Created by acceleration of massive compact objects
Gravitational wave detectors measure changes in L-L the separation between free test masses in this spacetime
◼
L+L Interferometric Detectors
Interferometers monitor the position of suspended test masses separated by a few km
A passing gravitational wave will lengthen one arm and shrink the other arm; transducer of GW strain- intensity (10-18 m over 4 km)
10-5m
41016m Ground-based network of detectors: 2002-2010
LIGO GEO600 Hanford TAMA, CLIO 300 m 600 m 4 km 100 m 2 km
LIGO LIGO VIRGO 3 km LivingstonLivingston
4 km From Initial to Advanced LIGO
Developed in Glasgow, 10kg test masses on simple pendulums become 40kg UK supplied: monolithic suspensions in fused silica quadruple pendulums, with better quality optics suspensions, fibre-pulling, bonding and welding GW150914 – a burst of gravitational waves… … matching a BBH inspiral and merger waveform from General Relativity
Abbott, et al., LIGO Scientific Collaboration and Virgo Collaboration, “Properties of the binary black hole merger GW150914”, https://arxiv.org/abs/1602.03840 Does General Relativity really fit?
• GW150914 was the first observation of a binary black hole merger • Our best test of GR in the strong field, dynamical, nonlinear regime • Constraints better than the binary pulsar system PSR J0737-3039
Post-Newtonian Approximation to GR Compton Wavelength of the Graviton
Abbott, et al., LIGO Scientific Collaboration and Virgo Collaboration, “Tests of general relativity with GW150914”, https://arxiv.org/abs/1602.03841 Abbott, et al., “GW170104: Further tests of General Relativity: GW170104 Observation of a 50-solar binary black hole coalescence at redshift 0.2” https://arxiv.org/abs/1706.01812 Parameterised test of PN expansion
Modified dispersion relation
Lower limit on QG energy scale With three or more interferometers we can triangulate the sky position of a gravitational wave source much more precisely.
Source location
Advanced Virgo joined O2 on Aug 1st 2017
Much better From Aasi et al., https://arxiv.org/abs/1304.0670 sky localisation Polarisation tests: GW170814
Abbott, et al., LIGO Scientific Collaboration and Virgo Collaboration, “GW170814: A Three-Detector Observation of Gravitational Waves from a Binary Black Hole Coalescence”, https://arxiv.org/abs/1709.09660
Likelihood function Antenna patterns See also Isi et al. arxiv:1703.05730 and Abbott et al. arxiv:1709.09203: p(Tensor) p(Tensor) > 200 > 1000 First search for non-tensorial continuous p(Vector) p(Scalar) GWs from known pulsars Abbott et al., “GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Binary Mergers Observed by LIGO and Virgo During the First and Second Observing Runs”, http://arxiv.org/abs/1811.12907 Abbott, et al., “Tests of General Relativity Improved Tests of GR With the GWTC-1 BBHs with the Binary Black Hole Signals from the LIGO-Virgo Catalog GWTC-1” arxiv.org/1903.04467 Constraining the speed of gravity: GW170817
Abbott et al., “Gravitational Waves and Gamma-rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A”, https://arxiv.org/abs/1710.05834 Tests of GR, nuclear EoS with GW170817
Abbott et al., “Tests of General Relativity with GW170817”, Abbott et al., “GW170817: Measurements of Neutron Star Radii https://arxiv.org/abs/1811.00364 and Equation of State”, https://arxiv.org/abs/1805.11581
Cosmology with Standard Sirens
Schutz, “Determining the Hubble Constant from gravitational wave observation” Nature, 323, 310 (1986)
Independent route to the Hubble Constant Tension between:
• Measurement of H0 from cosmic distance ladder
(e.g. SH0ES)
• Inference of H0 from CMBR / LSS and cosmological model (e.g. Planck)
Tension increases in e.g. Riess et al. 1903.07603:
Freedman, “Cosmology at a Crossroads: Tension with the Hubble Constant”, https://arxiv.org/abs/1706.02739 Maximum minimal posterior value 68% C.I.
Abbott et al. “A Gravitational Wave Standard Siren Measurement of the Hubble Constant“ Nature, 551, 85 (2017) https://dcc.ligo.org/public/0145/P1700296/005/LIGO-P1700296.pdf Abbott et al., “Tests of General Relativity with GW170817”, Number of spacetime dimensions: GW170817 https://arxiv.org/abs/1811.00364
Can compare EM and GW luminosity distance – Pardo et al., “Limits on the number of spacetime dimensions these scale differently in many higher-D models. from GW170817”, https://arxiv.org/abs/1811.00364
Adopt simple phenomenological model: Computed Bayesian posterior on D, fixing EM luminosity distance to Planck or SHoES Hubble constant
Computed Bayesian posterior on D, for different fixed values of the screening scale
Proximity of GW170817 limits effectiveness of constraints so far, but watch this space(-time)!… We can also use “dark sirens” – no explicit EM counterpart We ‘marginalise’ over the redshifts of possible host galaxies Useful ‘proof of concept’
Soares-Santos et al., “First measurement of the Hubble constant from a dark standard siren using the Dark Energy Survey galaxies and the LIGO/Virgo binary black hole merger GW170814”, http://arxiv.org/abs/1901.01540 Network of advanced detectors
Advanced LIGO Hanford GEO600 (HF)
Advanced Virgo
Advanced LIGO KAGRA Livingston
LIGO-India Coming attractions…
Nissanke et al., “Determining the Hubble constant from gravitational-wave observations of merging compact binaries”, https://arxiv.org/abs/1307.2638 Coming attractions…
Chen et al., “Precision Standard Siren Cosmology”, https://arxiv.org/abs/1712.06531 Cowperthwaite et al., “Joint Gravitational Wave and Electromagnetic Astronomy with LIGO and LSST in the 2020s”, https://arxiv.org/abs/1712.06531 Third Generation GW Network
Aimed at having excellent sensitivity from ~1 Hz to ~104 Hz.
FP7 European design study: the Einstein Telescope (ET). Goal: 100 times better sensitivity than first generation instruments.
See http://www.et-gw.eu/ See also Dwyer et al. arxiv: 1410.0612 US-led project: “Cosmic Explorer” http://www.cosmicexplorer.org/
https://gwic.ligo.org/3Gsubcomm/ Cosmological constraints BNS: ET-D + CE from 3G detectors
Zhao & Wen: http://arxiv.org/abs/1710.05325
See also Zhao et al. http://arxiv.org/abs/1009.0206
~106 NS-NS mergers observed by 3G networks Different models for spatial distribution, source evolution z w(z) = w + w 0 a 1+ z
GW constraints similar to those from BAO, SNIe.
BUT assumes z known for ~1000 sources, z < 2
Significant ‘multi-messenger’ challenge Correcting for Weak Lensing?... Shapiro et al. arxiv:0907.3635 GW sources will be (de-)magnified by weak lensing due to LSS No correction
Shear map only, ELT Shapiro et al (2010): Shear varies spatially Gradient of shear → arcing, or flexion
Shear + flexion, Shear + flexion, ELT ELT + Space
Assume we can measure flexion from galaxy surveys, giving better estimate of matter density on small angular scales.
DL → 1.8% at z = 2
DL → 1.4% at z =1 Euclid EELT The Gravitational Wave Spectrum Supernovae Cosmic Strings BH and NS Binaries Relic radiation
Extreme Mass Ratio Inspirals
Supermassive BH Binaries Binaries coalescences Spinning NS
10-16 Hz 10-9 Hz 10-4 Hz 100 Hz 103 Hz Inflation Probe Pulsar timing Space detectors Ground based
Adapted from M. Evans (LIGO G1300662-v4)
LISA will ‘see’ very high-SNR massive black hole binary mergers to z > 20 • Exquisite tests of GR from waveforms • Standard siren Hubble diagram to high redshift
Long tail due to parameter degeneracies
Holz and Hughes 2005 Colpi et al. 2019 Extreme Mass Ratio Inspirals
• Among the most interesting and important low-frequency sources, probing fundamental physics, astrophysics and cosmology: ➢ Study immediate environment of MW-like MBHs at low redshift ➢ Perform precision tests of GR ➢ Explore multipolar structure of MBH gravitational fields ➢ Test GW propagation properties ➢ Measure cosmic expansion rate with GW observations alone (“dark sirens”) ➢ Probe dynamics of dense nuclear star clusters
Long, complex waveforms; major data analysis challenge! Constraining extra-D models with LISA Realistic LISA data constrain well and .
Corman and Hendry (in prep.) But for better with steep transition.
Bayes factors strongly depend on errors, weakly depend on MBH formation model
Heavy ‘seeds’, no delay arxiv:1901.02674 Strong Lensing of GWs?... …Not yet, but clear future potential
For example: diagnostic of wave dark matter Schive et al. “Cosmic structure as the quantum interference of a coherent dark wave”, arxiv:1406.6586 See also e.g. these arxiv papers on constraints from A. Herrera Martin (2018) lensed GW+EM systems : 1901.10638; 1809.07079; “Wave dark matter as a gravitational lens 1703.04151; 1612.04095; 1508.05000 for electromagnetic and gravitational waves” http://theses.gla.ac.uk/9027/ GWs and Primordial Black Holes? arxiv:1603.00464
Carr et al., https://arxiv.org/abs/1607.06077
Possible mass window in LIGO BH mass range?... Useful discriminator could be isotropy of BH spins: • Random alignment for PBH origin models • Aligned distribution for other scenarios Abbott et al., http://arxiv.org/abs/1811.12907 Summary: Lots of coming attractions.... • Improved tests of GR: ➢ P-N orders; Compton wavelength ➢ polarisation constraints (from ➢ speed of gravity – EM arrival, dispersion ➢ EMRI mapping spacetime around SMBHs ➢ joint GW-EM observations of lensed sources • Constraining non-standard cosmologies: ➢ Hubble diagram of sirens; event rates ➢ Primordial BHs – strong constraints from spin distribution ➢ Strong lensing by DM haloes: probe of wave DM? ➢ ????