From Einstein to Gravitational Waves and Beyond … Barry C Barish Caltech Workshop on Kamioka Underground Physics Okayama University 23-May-2017 LIGO-G1700695 for the LIGO Scientific Collaboration and Virgo Collaboration
100 Years Ago -- 1916 Einstein Predicted Gravitational Waves • 1st publication indicating the existence of gravitational waves by Einstein in 1916 • Contained errors relating wave amplitude to source motions • 1918 paper corrected earlier errors (factor of 2), and it contains the LIGO-G1700695 quadrupole formula for radiating source
BUT, the effect is incredibly small • Consider ~30 solar mass binary Merging Black Holes – M = 30 M R = 100 km f = 100 Hz r = 3 10 24 m (500 Mpc) 2 2 2 4 GMR f 21 h L / L orb h ~ 10 4 c r 23-May-2017 3 Workshop on Kamioka Underground Physics Credit: T. Strohmayer and D. Berry
Emission of Gravitational Waves 23-May-2017 4 Workshop on Kamioka Underground Physics
Workshop on Kamioka Underground 23-May-2017 5 Physics
Compact Binary Collisions – Neutron Star – Neutron Star • waveforms are well described – Black Hole – Black Hole • Numerical Relativity waveforms – Search: matched templates “chirps” Workshop on Kamioka Underground 23-May-2017 6 Physics
hg Observed Signals – Sept 14, 2015 September 14, 2015 Workshop on Kamioka Underground 23-May-2017 7 Physics
Einstein’s Theory of Gravitation Gravitational Waves • Using Minkowski metric, the information about space- time curvature is contained in the metric as an added 2 1 term, h . In the weak field limit, the equation can be 2 ( ) h 0 described with linear equations. If the choice of gauge 2 2 c t is the transverse traceless gauge the formulation becomes a familiar wave equation • The strain h takes the form of a plane wave propagating at the speed of light (c). • Since gravity is spin 2, the waves have two components, but rotated by 45 0 instead of 90 0 h h ( t z / c ) h ( t z / c ) x from each other . Workshop on Kamioka Underground 23-May-2017 8 Physics
Gravitational waves • Predicted by Einstein’s theory of General Relativity • Ripples of spacetime that stretch and L compress spacetime itself • The amplitude of the wave is h ≈ 10 -21 • Change the distance between masses Δ that are free to move by Δ L = h x L L • Spacetime is “stiff” so changes in distance are very small Workshop on Kamioka Underground 23-May-2017 9 Physics
Suspended Mass Interferometry Workshop on Kamioka Underground 23-May-2017 10 Physics
LIGO Sites Siting LIGO Workshop on Kamioka Underground 23-May-2017 11 Physics
LIGO Construction Began in 1994
LIGO Interferometers Hanford, WA Livingston, LA Workshop on Kamioka Underground 23-May-2017 13 Physics
LIGO LIGO Infrastructure beam tube
LIGO Interferometer Infrastructure Workshop on Kamioka Underground 23-May-2017 15 Physics
Interferometer Noise Limits Seismic Noise test mass (mirror) Quantum Noise Residual gas scattering Radiation pressure "Shot" noise LASER Beam splitter Wavelength & Thermal amplitude (Brownian) fluctuations photodiode Noise Workshop on Kamioka Underground 23-May-2017 16 Physics
What Limits LIGO Sensitivity? Seismic noise limits low frequencies Thermal Noise limits middle frequencies Quantum nature of light (Shot Noise) limits high frequencies Technical issues - alignment, electronics, acoustics, etc limit us before we reach these design goals - Workshop on Kamioka Underground 23-May-2017 17 Physics
Evolution of LIGO Sensitivity Workshop on Kamioka Underground 23-May-2017 18 Physics
Initial LIGO Performance (Final) Workshop on Kamioka Underground 23-May-2017 19 Physics
Advanced LIGO GOALS GO G Better seismic isolation Higher Better test power masses laser and suspension LIGO-G1700695
How to obtain a x10 sensitivity improvement? Parameter Initial LIGO Advanced LIGO Input Laser Power 10 W 180 W (10 kW arm) (>700 kW arm) Mirror Mass 10 kg 40 kg Interferometer Power-recycled Dual-recycled Topology Fabry-Perot arm Fabry-Perot arm cavity Michelson cavity Michelson (stable recycling cavities) Laser EO M GW Readout RF heterodyne DC homodyne Method 3 x 10 -23 / rHz Optimal Strain Tunable, better than 5 x 10 -24 / rHz Sensitivity in broadband Seismic Isolation f low ~ 50 Hz f low ~ 13 Hz Performance Mirror Single Pendulum Quadruple - Workshop on Kamioka Underground 23-May-2017 Suspensions pendulum 21 Physics
Mirror / Test Masses • Mechanical requirements: bulk and coating thermal noise, high resonant frequency • Optical requirements: figure, scatter, homogeneity, bulk and coating absorption 40 kg Test Masses: 34cm x 20cm Round-trip optical loss: 75 ppm max 40 kg Compensation plates: 34cm x 10cm BS: 37cm x 6cm ITM Workshop on Kamioka Underground T = 1.4% 23-May-2017 22 Physics
Seismic Isolation suspension system suspension assembly for a core optic • support structure is welded tubular stainless steel • suspension wire is 0.31 mm diameter steel music wire • fundamental violin mode frequency of 340 Hz Workshop on Kamioka Underground 23-May-2017 23 Physics
Test Mass Quadruple Pendulum Suspension Optics Table Interface (Seismic Isolation System ) Damping Controls Hierarchical Global Controls Final elements All Fused silica Electrostatic Actuation Workshop on Kamioka Underground 23-May-2017 24 Physics
Passive Seismic Isolation Initial ILIGO Constrained Layer damped spring Workshop on Kamioka Underground 23-May-2017 25 Physics
Virgo Seismic Performance Workshop on Kamioka Underground 23-May-2017 26 Physics
Seismic Isolation Passive / Active Multi-Stage Workshop on Kamioka Underground 23-May-2017 27 Physics
200W Nd:YAG laser Designed and contributed by Max Planck Albert Einstein Institute • Stabilized in power and frequency • Uses a monolithic master oscillator followed by injection-locked rod amplifier 23-May-2017 Workshop on Kamioka Underground Physics 28
Sensitivity for first Observing run At ~40 Hz, Broadband, Factor ~100 Factor ~3 improvement Initial LIGO improvement O1 aLIGO Design aLIGO Phys. Rev. D 93, 112004 (2016 23-May-2017 29 Workshop on Kamioka Underground Physics
Gravitational Wave Event GW150914 Data bandpass filtered between 35 Hz and 350 Hz Time difference 6.9 ms with Livingston first Second row – calculated GW strain using Numerical Relativity Waveforms for quoted parameters compared to reconstructed waveforms (Shaded) Third Row – residuals bottom row – time frequency plot showing frequency increases with time (chirp) 23-May-2017 Phys. Rev. Lett. 116, 061102 (2016) Workshop on Kamioka Underground Physics 30
Black Hole Merger Events and Low Frequency Sensitivity GW150914 GW151226 23-May-2017 31 Workshop on Kamioka Underground Physics
Sensitivity of Initial LIGO-Virgo Astrophys.J. 760 (2012) 12 arXiv:1205.2216 [astro-ph.HE] LIGO-P1000121 Workshop on Kamioka Underground 23-May-2017 32 Physics
Statistical Significance of GW150914 Binary Coalescence Search Phys. Rev. Lett. 116, 061102 (2016) 23-May-2017 33 Workshop on Kamioka Underground Physics
Black Hole Merger: GW150914 Phys. Rev. Lett. 116, 061102 (2016) Full bandwidth waveforms without filtering. Numerical relativity models of black hole horizons during coalescence Effective black hole separation in units of Schwarzschild radius (R s =2GM f / c 2 ); and effective relative velocities given by post- Newtonian parameter v/c = (GM f f/c 3 ) 1/3 23-May-2017 Workshop on Kamioka Underground Physics 34
Measuring the parameters • Orbits decay due to emission of gravitational waves – Leading order determined by “chirp mass” – Next orders allow for measurement of mass ratio and spins – We directly measure the red-shifted masses (1+z) m – Amplitude inversely proportional to luminosity distance • Orbital precession occurs when spins are misaligned with orbital angular momentum – no evidence for precession. • Sky location, distance, binary orientation information extracted from time-delays and differences in observed amplitude and phase in the detectors 23-May-2017 Workshop on Kamioka Underground Physics 35
Black Hole Merger Parameters for GW150914 Use numerical simulations fits of black hole Phys. Rev. Lett. 116, 241102 (2016) merger to determine parameters; determine total energy radiated in gravitational waves is 3.0 ±0.5 M o c 2 . The system reached a peak ~3.6 x10 56 ergs, and the spin of the final black hole < 0.7 (not maximal spin) Workshop on Kamioka Underground Phys. Rev. Lett. 116, 061102 (2016) 23-May-2017 36 Physics
Image credit: LIGO More Events? Workshop on Kamioka Underground 23-May-2017 37 Physics
Finding a weak signal in noise • “Matched filtering” lets us find a weak signal submerged in noise. For calculated signal waveforms, multiply the • waveform by the data Find signal from cumulative signal/noise • PHYS. REV. X 6,041015 (2016) 38
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