LIGO and the Quest for Gravitational Waves Colliding

LIGO and the Quest for Gravitational Waves "Colliding Black Holes" Credit: National Center for Supercomputing Applications (NCSA) LIGO-G 030523 -00 -M Barry C. Barish Caltech UT Austin 24 -Sept-03 1

A Conceptual Problem is solved ! Newton’s Theory “instantaneous action at a distance” Gmn= 8 p. Tmn Einstein’s Theory information carried by gravitational radiation at the speed of light 2

Einstein’s Theory of Gravitation § a necessary consequence of Special Relativity with its finite speed for information transfer § gravitational waves come from the acceleration of masses and propagate away from their sources as a space-time warpage at the speed of light gravitational radiation binary inspiral of compact objects 3

Einstein’s Theory of Gravitation gravitational waves • Using Minkowski metric, the information about space-time curvature is contained in the metric as an added term, hmn. In the weak field limit, the equation can be described with linear equations. If the choice of gauge is the transverse traceless gauge the formulation becomes a familiar wave equation • The strain hmn 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 450 instead of 900 from each other. 4

The evidence for gravitational waves Hulse & Taylor · • • m 1 = 1. 4 m 17 / sec · Neutron binary system • separation = 106 miles • m 2 = 1. 36 m • e = 0. 617 period ~ 8 hr PSR 1913 + 16 Timing of pulsars Prediction from general relativity • spiral in by 3 mm/orbit • rate of change orbital period 5

“Indirect” detection of gravitational waves PSR 1913+16 6

Detection of Gravitational Waves Gravitational Wave Astrophysical Source Terrestrial detectors Detectors in space Virgo, LIGO, TAMA, GEO AIGO LISA 7

Frequency range for EM astronomy Electromagnetic waves § over ~16 orders of magnitude § Ultra Low Frequency radio waves to high energy gam 8

Frequency range for GW Astronomy Audio band Gravitational waves § over ~8 orders of magnitude § Terrestrial and space detectors Space Terrestrial 9

International Network on Earth simultaneously detect signal LIGO GEO decompose detection locatethe confidence polarization sources of gravitational waves Virgo TAMA AIGO 10

The effect … Leonardo da Vinci’s Vitruvian man Stretch and squash in perpendicular directions at the frequency of the gravitational waves 11

Detecting a passing wave …. Free masses 12

Detecting a passing wave …. Interferometer 13

The challenge …. I have greatly exaggerated the effect!! If the Vitruvian man was 4. 5 light years high, he would grow by only a ‘hairs width’ Interferometer Concept 14

Interferometer Concept § Arms in LIGO are 4 km § Laser used to measure relative § Measure difference in lengths of two length to one part in 1021 orthogonal arms or 10 -18 meters …causing the interference pattern to change at the photodiode As a wave Suspended passes, the Masses arm lengths change in different ways…. 15

How Small is 10 -18 Meter? One meter ~ 40 inches Human hair ~ 100 microns Wavelength of light ~ 1 micron Atomic diameter 10 -10 m Nuclear diameter 10 -15 m LIGO sensitivity 10 -18 m 16

Simultaneous Detection LIGO Hanford Observatory MIT Caltech Livingston Observatory 17

LIGO Livingston Observatory 18

LIGO Hanford Observatory 19

LIGO Facilities beam tube enclosure • minimal enclosure • reinforced concrete • no services 20

LIGO beam tube § LIGO beam tube under con § 65 ft spiral welded section § girth welded in portable cl 1. 2 m diameter - 3 mm stainless 50 km of weld 21

Vacuum Chambers vibration isolation systems » Reduce in-band seismic motion by 4 - 6 orders of magnitude » Compensate for microseism at 0. 15 Hz by a factor of ten » Compensate (partially) for Earth tides 22

Seismic Isolation springs and masses Constrained Layer damped spring 23

LIGO vacuum equipment 24

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 25

LIGO Optics fused silica § § § Caltech data Surface uniformity < 1 nm rms Scatter < 50 ppm Absorption < 2 ppm ROC matched < 3% Internal mode Q’s > 2 x 106 CSIRO data 26

Core Optics installation and alignment 27

Locking the Interferometers 28

Lock Acquisition 29

Making LIGO Work 30

Detecting Earthquakes From electronic logbook 2 -Jan-02 An earthquake occurred, starting at UTC 17: 38. 31

Detecting the Earth Tides Sun and Moon Eric Morgenson Caltech Sophomore 32

Tidal Compensation Data Tidal evaluation 21 -hour locked section of S 1 data Predicted tides Feedforward Feedback Residual signal on voice coils Residual signal on laser 33

Controlling angular degrees of freedom 34

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 35

LIGO Sensitivity Livingston 4 km Interferometer First Science Run 17 days - Sept 02 May 01 Jan 03 Second Science Run 59 days - April 03 36

Astrophysical Sources signatures § Compact binary inspiral: “chirps” » NS-NS waveforms are well described » BH-BH need better waveforms » search technique: matched templates § Supernovae / GRBs: “bursts” » burst signals in coincidence with signals in electromagnetic radiation » prompt alarm (~ one hour) with neutrino detectors § Pulsars in our galaxy: “periodic” » search for observed neutron stars (frequency, doppler shift) » all sky search (computing challenge) » r-modes § Cosmological Signal “stochastic background” 37

Compact binary collisions » Neutron Star – waveforms are well described » Black Hole – need better waveforms » Search: matched templates “chirps” 38

Template Bank § Covers desired region of mass param space § Calculated based on L 1 noise curve § Templates placed for max mismatch of = 0. 03 2110 templates Second-order post-Newtonian 39

Optimal Filtering frequency domain § Transform data to frequency domain : § Generate template in frequency domain : § Correlate, weighting by power spectral density of noise: Then inverse Fourier transform gives you the filter output at all times: Find maxima of over arrival time and phase Characterize these by signal-to-noise ratio (SNR) and effective distance 40

Matched Filtering 41

Loudest Surviving Candidate § § Not NS/NS inspiral event 1 Sep 2002, 00: 38: 33 UTC S/N = 15. 9, c 2/dof = 2. 2 (m 1, m 2) = (1. 3, 1. 1) Msun What caused this? § Appears to be due to saturation of a photodiode 42

Sensitivity neutron binary inspirals Star Population in our Galaxy § Population includes Milky Way, LMC and SMC § Neutron star masses in range 1 -3 Msun § LMC and SMC contribute ~12% of Milky Way Reach for S 1 Data § Inspiral sensitivity Livings Hanford: <D> = 36 kpc § Sensitive to inspirals in Milk 43

Results of Inspiral Search Upper limit binary neutron star coalescence rate LIGO S 1 Data R < 160 / yr / MWEG § Previous observational limits » Japanese TAMA » Caltech 40 m § Theoretical prediction R < 30, 000 / yr / MWEG R < 4, 000 / yr / MWEG R < 2 x 10 -5 / yr / MWEG Detectable Range of S 2 data will reach Andromeda! 44

Astrophysical Sources signatures § Compact binary inspiral: “chirps” » NS-NS waveforms are well described » BH-BH need better waveforms » search technique: matched templates § Supernovae / GRBs: “bursts” » burst signals in coincidence with signals in electromagnetic radiation » prompt alarm (~ one hour) with neutrino detectors § Pulsars in our galaxy: “periodic” » search for observed neutron stars (frequency, doppler shift) » all sky search (computing challenge) » r-modes § Cosmological Signal “stochastic background” 45

Detection of Burst Sources § Known sources -- Supernovae & GRBs » Coincidence with observed electromagnetic observations. » No close supernovae occurred during the first science run » Second science run – We are analyzing the recent very bright and close GRB 030329 NO RESULT YET § Unknown phenomena » Emission of short transients of gravitational radiation of unknown waveform (e. g. black hole mergers). 46

‘Unmodeled’ Bursts GOAL search for waveforms from sources for which we cannot currently make an accurate prediction of the waveform shape. METHODS ‘Raw Data’ Time-domain high pass filter frequency Time-Frequency Plane Search ‘TFCLUSTERS’ Pure Time-Domain Search ‘SLOPE’ 8 Hz 0. 125 s time 47

Determination of Efficiency measured for ‘tfclusters’ algorithm To measure our efficiency, we must pick a waveform. amplitude h 0 0 time (ms) 10 1 ms Gaussian burst 48

Burst Upper Limit from S 1 1 ms gaussian bursts Result is derived using ‘TFCLUSTERS’ algorithm 90% confidence Upper limit in strain compared to earlier (cryogenic bar) results: • IGEC 2001 combined bar upper limit: < 2 events per day having h=1 x 10 -20 per Hz of burst bandwidth. For a 1 k. Hz bandwidth, limit is < 2 events/day at h=1 x 10 -17 • Astone et al. (2002), report a 2. 2 s excess of one event per day at strain level of h ~ 2 x 10 -18 49

Astrophysical Sources signatures § Compact binary inspiral: “chirps” » NS-NS waveforms are well described » BH-BH need better waveforms » search technique: matched templates § Supernovae / GRBs: “bursts” » burst signals in coincidence with signals in electromagnetic radiation » prompt alarm (~ one hour) with neutrino detectors § Pulsars in our galaxy: “periodic” » search for observed neutron stars (frequency, doppler shift) » all sky search (computing challenge) » r-modes § Cosmological Signal “stochastic background” 50

Detection of Periodic Sources § Pulsars in our galaxy: “periodic” » search for observed neutron stars » all sky search (computing challenge) » r-modes § Frequency modulation of signal due to Earth’s motion relative to the Solar System Barycenter, intrinsic frequency changes. §Amplitude modulation due to the detector’s antenna pattern. 51

Directed searches NO DETECTION EXPECTED at present sensitivities Crab Pulsar Limits of detectability for rotating NS with equatorial ellipticity e = I/Izz: 10 -3 , 10 -4 , 10 -5 @ 8. 5 kpc. PSR J 1939+2134 1283. 86 Hz 52

Two Search Methods Frequency domain • Best suited for large parameter space searches • Maximum likelihood detection method + Frequentist approach Time domain • Best suited to target known objects, even if phase evolution is complicated Bayesian approach First science run --- use both pipelines for the same search for cross-checking and validation 53

The Data time behavior days 54

The Data frequency behavior Hz Hz 55

PSR J 1939+2134 Frequency domain • Fourier Transforms of time series Injected signal in LLO: h = 2. 83 x 10 -22 • Detection statistic: F , maximum likelihood ratio wrt unknown parameters • use signal injections to measure F’s pdf Measured F statistic • use frequentist’s approach to derive upper limit 56

PSR J 1939+2134 Data Time domain Injected signals in GEO: h=1. 5, 2. 0, 2. 5, 3. 0 x 10 -21 • time series is heterodyned • noise is estimated • Bayesian approach in parameter estimation: express result in terms of posterior pdf for parameters of interest 95% h = 2. 1 x 10 -21 57

Results: Periodic Sources § No evidence of continuous wave emission from PSR J 1939+2134. § Summary of 95% upper limits on h: IFO Frequentist FDS Bayesian TDS GEO (1. 94 0. 12)x 10 -21 (2. 1 0. 1)x 10 -21 LLO (2. 83 0. 31)x 10 -22 (1. 4 0. 1)x 10 -22 LHO-2 K (4. 71 0. 50)x 10 -22 (2. 2 0. 2)x 10 -22 LHO-4 K (6. 42 0. 72)x 10 -22 (2. 7 0. 3)x 10 -22 • Best previous results for PSR J 1939+2134: ho < 10 -20 (Glasgow, Hough et al. , 1983) 58

Upper limit on pulsar ellipticity J 1939+2134 moment of inertia tensor gravitational ellipticity of pulsar h 0 < 3 10 -22 e < 3 10 -4 R (M=1. 4 Msun, r=10 km, R=3. 6 kpc) Assumes emission is due to deviation from axisymmetry: . . 59

Astrophysical Sources signatures § Compact binary inspiral: “chirps” » NS-NS waveforms are well described » BH-BH need better waveforms » search technique: matched templates § Supernovae / GRBs: “bursts” » burst signals in coincidence with signals in electromagnetic radiation » prompt alarm (~ one hour) with neutrino detectors § Pulsars in our galaxy: “periodic” » search for observed neutron stars (frequency, doppler shift) » all sky search (computing challenge) » r-modes § Cosmological Signal “stochastic background” 60

Signals from the Early Universe stochastic background Cosmic Microwave background WMAP 2003 61

Signals from the Early Universe § Strength specified by ratio of energy density in GWs to total energy density needed to close the universe: § Detect by cross-correlating output of two GW detectors: First LIGO Science Data Hanford - Livingston 62

Limits: Stochastic Search Interferometer Pair 90% CL Upper Limit Tobs LHO 4 km-LLO 4 km WGW (40 Hz - 314 Hz) < 72. 4 62. 3 hrs LHO 2 km-LLO 4 km WGW (40 Hz - 314 Hz) < 23 61. 0 hrs § Non-negligible LHO 4 km-2 km (H 1 -H 2) instrumental crosscorrelation; currently being investigated. § Previous best upper limits: » Garching-Glasgow interferometers : » EXPLORER-NAUTILUS (cryogenic bars): 63

Gravitational Waves from the Early Universe results projected E 7 S 1 S 2 LIGO Adv LIGO 64

Advanced LIGO improved subsystems Multiple Suspensions Active Seismic Sapphire Optics Higher Power Laser 65

Advanced LIGO Cubic Law for “Window” on the Universe Improve amplitude sensitivity by a factor of 10 x… …number of sources goes up 1000 x! Virgo cluster Initial LIGO Advanced LIGO 66

Advanced LIGO 2007 + Enhanced Systems • laser • suspension • seismic isolation • test mass Rate Improvement ~ 104 + narrow band optical configuration 67

LIGO § Construction is complete & commissioning is well underway § New upper limits for neutron binary inspirals, a fast pulsar and stochastic backgrounds have been achieved from the first short science run § Sensitivity improvements are rapid -- second data run was 10 x more sensitive and 4 x duration and results will be reported soon. § Enhanced detectors will be installed in ~ 5 years, further increasing sensitivity § Direct detection should be achieved and gravitational-wave astronomy begun within the next decade ! 68

Gravitational Wave Astronomy LIGO will provide a new way to view the dynamics of the Universe 69