Probing the Universe for Gravitational Waves A First

Probing the Universe for Gravitational Waves: A First Glimpse with LIGO Barry C. Barish Caltech "Colliding Black Holes" Credit: National Center for Supercomputing Applications (NCSA) LIGO-G 030020 -00 -M 10 -April-03 Penn State -- Colloquium Penn State 10 -April-03

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 10 -April-03 Penn State -- Colloquium 2

Einstein’s Theory of Gravitation § a necessary consequence of Special Relativity with its finite speed for information transfer § gravitational waves come from gravitational radiation binary inspiral of compact objects 10 -April-03 the acceleration of masses and propagate away from their sources as a space-time warpage at the speed of light Penn State -- Colloquium 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. 10 -April-03 Penn State -- Colloquium 4

Detecting Gravitational Waves Laboratory Experiment a la Hertz Experimental Generation and Detection of Gravitational Waves gedanken experiment 10 -April-03 Penn State -- Colloquium 5

The evidence for gravitational waves Neutron binary system Hulse & Taylor · • separation = 106 miles • m 1 = 1. 4 m • m 2 = 1. 36 m • e = 0. 617 17 / sec · PSR 1913 + 16 Timing of pulsars 10 -April-03 • Prediction from general relativity period ~ 8 hr • spiral in by 3 mm/orbit • rate of change orbital period Penn State -- Colloquium 6

“Indirect” detection of gravitational waves PSR 1913+16 10 -April-03 Penn State -- Colloquium 7

Direct Detection Gravitational Wave Astrophysical Source Terrestrial detectors LIGO, TAMA, Virgo, AIGO Detectors in space LISA 10 -April-03 Penn State -- Colloquium 8

Detection in space The Laser Interferometer Space Antenna LISA § Center of the triangle formation is in the ecliptic plane § 1 AU from the Sun and 20 degrees behind the Earth. 10 -April-03 Penn State -- Colloquium 9

Detection on Earth simultaneously detect signal LIGO GEO decompose the polarization of detection locate theconfidence sources gravitational waves 10 -April-03 Penn State -- Colloquium Virgo TAMA AIGO 10

Frequency range of astrophysics sources Audio band § Gravitational Waves over ~8 orders of magnitude » Terrestrial detectors and space detectors Space 10 -April-03 Penn State -- Colloquium Terrestrial 11

Frequency range of astronomy § EM waves studied over ~16 orders of magnitude » Ultra Low Frequency radio waves to high energy gamma rays 10 -April-03 Penn State -- Colloquium 12

A New Window on the Universe Gravitational Waves will provide a new way to view the dynamics of the Universe 10 -April-03 Penn State -- Colloquium 13

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 Signals “stochastic background” 10 -April-03 Penn State -- Colloquium 14

The effect … Leonardo da Vinci’s Vitruvian man Stretch and squash in perpendicular directions at the frequency of the gravitational waves 10 -April-03 Penn State -- Colloquium 15

Detecting a passing wave …. Free masses 10 -April-03 Penn State -- Colloquium 16

Detecting a passing wave …. Interferometer 10 -April-03 Penn State -- Colloquium 17

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’ LIGO Interferometer Concept 10 -April-03 Penn State -- Colloquium 18

Interferometer Concept § Laser used to measure § Arms in LIGO are 4 km relative lengths of two § Measure difference in orthogonal arms length to one part in 1021 or 10 -18 meters …causing the interference pattern to change at the photodiode 10 -April-03 As a wave passes, the arm lengths change in different ways…. Penn State -- Colloquium 19

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 10 -April-03 Penn State -- Colloquium 20

LIGO Organization DESIGN CONSTRUCTION OPERATION Detector R&D SCIENCE LIGO Laboratory LIGO Science Collaboration MIT + Caltech 44 member institutions ~140 people > 400 scientists Director: Barry Barish Spokesperson: Rai Weiss UK Germany Japan Russia India Spain Australia $ National Science Foundation 10 -April-03 Penn State -- Colloquium 21

The Laboratory Sites Laser Interferometer Gravitational-wave Observatory (LIGO) Hanford Observatory Livingston Observatory 10 -April-03 Penn State -- Colloquium 22

LIGO Livingston Observatory 10 -April-03 Penn State -- Colloquium 23

LIGO Hanford Observatory 10 -April-03 Penn State -- Colloquium 24

LIGO beam tube 1. 2 m diameter - 3 mm stainless 50 km of weld 10 -April-03 § LIGO beam tube under constr § 65 ft spiral welded sections § girth welded in portable clean NO LEAKS !! Penn State -- Colloquium 25

LIGO vacuum equipment 10 -April-03 Penn State -- Colloquium 26

LIGO Optic Substrates: Si. O 2 25 cm Diameter, 10 cm thick Homogeneity < 5 x 10 -7 Internal mode Q’s > 2 x 106 Polishing Surface uniformity < 1 nm rms Radii of curvature matched < 3% Coating Scatter < 50 ppm Absorption < 2 ppm Uniformity <10 -3 10 -April-03 Penn State -- Colloquium 27

Core Optics installation and alignment 10 -April-03 Penn State -- Colloquium 28

Laser stabilization § Deliver pre-stabilized laser light to the 15 -m mode cleaner • Frequency fluctuations • In-band power fluctuations • Power fluctuations at 25 MHz Tidal § Provide actuator inputs for further stabilization • Wideband • Tidal Wideband 4 km 15 m 10 -Watt Laser PSL IO 10 -1 Hz/Hz 1/2 10 -4 Hz/ Hz 1/2 10 -April-03 Penn State -- Colloquium Interferometer 10 -7 Hz/ Hz 1/2 29

Prestabalized Laser performance 10 -April-03 Penn State -- Colloquium § > 20, 000 hours continuous operation § Frequency and lock very robust § TEM 00 power > 8 watts § Non-TEM 00 power < 10% § Simplification of beam path outside vacuum reduces peaks § Broadband spectrum better than specification from 40 -200 Hz 30

LIGO “first lock” Composite Video Y Arm Laser X Arm signal 10 -April-03 Penn State -- Colloquium 31

Watching the Interferometer Lock Y arm X arm 2 min Y Arm Reflected light Anti-symmetric port Laser X Arm signal 10 -April-03 Penn State -- Colloquium 32

Lock Acquisition 10 -April-03 Penn State -- Colloquium 33

What Limits Sensitivity of Interferometers? 1. Seismic noise & vibration limit at low frequencies 2. Atomic vibrations (Thermal Noise) inside components limit at mid frequencies 3. Quantum nature of light (Shot Noise) limits at high frequencies 4. Myriad details of the lasers, electronics, etc. , can make problems above these levels 10 -April-03 Penn State -- Colloquium 34

LIGO Sensitivity Livingston 4 km Interferometer May 01 Jan 03 10 -April-03 Penn State -- Colloquium 35

Detecting Earthquakes From electronic logbook 2 -Jan-02 An earthquake occurred, starting at UTC 17: 38. 10 -April-03 Penn State -- Colloquium 36

Detecting the Earth Tides Sun and Moon 10 -April-03 Penn State -- Colloquium 37

LIGO Sensitivity Livingston 4 km Interferometer First Science Run 17 days - Sept 02 May 01 Jan 03 Second Science Run 59 days - April 03 10 -April-03 Penn State -- Colloquium 38

In-Lock Data Summary from S 1 H 1: 235 hrs H 2: 298 hrs Red lines: integrated up time L 1: 170 hrs 3 X: 95. 7 hrs Green bands (w/ black borders): epochs of lock • August 23 – September 9, 2002: 408 hrs (17 days). • H 1 (4 km): duty cycle 57. 6% ; Total Locked time: 235 hrs • H 2 (2 km): duty cycle 73. 1% ; Total Locked time: 298 hrs • L 1 (4 km): duty cycle 41. 7% ; Total Locked time: 170 hrs • Double coincidences: • L 1 && H 1 : duty cycle 28. 4%; Total coincident time: 116 hrs • L 1 && H 2 : duty cycle 32. 1%; Total coincident time: 131 hrs • H 1 && H 2 : duty cycle 46. 1%; Total coincident time: 188 hrs Triple Coincidence: L 1, H 1, and H 2 : duty cycle 23. 4% ; total 95. 7 hours 10 -April-03 Penn State -- Colloquium 39

Compact binary collisions “chirps” » Neutron Star – waveforms are well described » Black Hole – need better waveforms » Search: matched templates Neutron Star Merger Simulation and Visualization by Maximilian Ruffert& Hans-Thomas Janka 10 -April-03 Penn State -- Colloquium 40

Searching Technique binary inspiral events § § Use template based matched filtering algorithm Template waveforms for non-spinning binaries » 2. 0 post-Newtonian approx. s(t) = (1 Mpc/D) x [ sin(a) h. Is (t-t 0) + cos(a) I (t-t 0)] h D: effective distance; a: c phase Discrete set of templates labeled by I=(m 1, m 2) » 1. 0 Msun < m 1, m 2 < 3. 0 Msun » 2110 templates » At most 3% loss in SNR 10 -April-03 Penn State -- Colloquium 41

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 Livingston: <D> = 176 kpc Hanford: <D> = 36 kpc § Sensitive to inspirals in » Milky Way, LMC & SMC 10 -April-03 Penn State -- Colloquium 42

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 saturation of a photodiode 10 -April-03 Penn State -- Colloquium 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 R < 30, 000 / yr / MWEG » Caltech 40 m R < 4, 000 / yr / MWEG § Theoretical prediction R < 2 x 10 -5 / yr / MWEG 10 -April-03 Penn State -- Colloquium 44

Gravitational Wave Bursts § Known phenomena like Supernovae & GRBs » Coincidence with observed electromagnetic observations. » No close supernovae occured 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). § Search methods: » Time domain algorithm (“SLOPE”): identifies rapid increase in amplitude of a filtered time series (threshold on ‘slope’). » Time-Frequency domain algorithm (“TFCLUSTERS”): identifies regions in the time-frequency plane with excess power 10 -April-03 Penn State -- Colloquium 45

‘Unmodelled’ 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 10 -April-03 Penn State -- Colloquium 46

Determination of Efficiency To measure our Efficiency measured for ‘tfclusters’ algorithm efficiency, we must pick a waveform. 1 ms Gaussian burst amplitude h 0 0 time (ms) 10 -April-03 10 Penn State -- Colloquium 47

Upper Limit 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 one sigma excess of one event per day at strain level of h ~ 2 x 10 -18 10 -April-03 Penn State -- Colloquium 48

Spinning Neutron Stars “periodic” An afterlife of stars 10 -April-03 Maximum gravitational wave luminosity of known pulsars Penn State -- Colloquium 49

Directed searches NO DETECTION EXPECTED at present sensitivities PSR J 1939+2134 10 -April-03 Penn State -- Colloquium 1283. 86 Hz 50

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 10 -April-03 Penn State -- Colloquium 51

The Data time behavior days 10 -April-03 Penn State -- Colloquium days 52

The Data frequency behavior 10 -April-03 Hz Hz Penn State -- Colloquium 53

PSR J 1939+2134 Frequency domain Injected signal in LLO: h = 2. 83 x 1022 • Fourier Transforms of time series • 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 10 -April-03 Penn State -- Colloquium 54

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 10 -April-03 Penn State -- Colloquium 95% h = 2. 1 x 10 -21 55

Results: Periodic Sources J 1939+2134 § 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 Joint - (1. 0 0. 1)x 10 -22 • ho<1. 0 x 10 -22 constrains ellipticity < 7. 5 x 10 -5 (M=1. 4 Msun, r=10 km, R=3. 6 kpc) • Previous results for PSR J 1939+2134: ho < 10 -20 (Glasgow, Hough et al. , 1983), ho < 3. 1(1. 5)x 10 -17 (Caltech, Hereld, 1983). 10 -April-03 Penn State -- Colloquium 56

Early Universe “correlated noise” ‘Murmurs’ from the Big Bang Cosmic Microwave background WMAP 2003 10 -April-03 Penn State -- Colloquium 57

Stochastic Background no observed correlations § 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 10 -April-03 Hanford - Hanford Penn State -- Colloquium 58

Stochastic Background sensitivities and theory E 7 results projected S 1 S 2 LIGO Adv LIGO 10 -April-03 Penn State -- Colloquium 59

Advanced LIGO improved subsystems Multiple Suspensions Active Seismic Sapphire Optics Higher Power Laser 10 -April-03 Penn State -- Colloquium 60

Advanced LIGO 2007 + • • Enhanced Systems laser suspension seismic isolation test mass Improvement factor in rate ~ 104 + narrow band optical configuration 10 -April-03 Penn State -- Colloquium 61

Probing the Universe with LIGO a first glimpse § LIGO commissioning is well underway » Good progress toward design sensitivity § Science Running is beginning » Initial results from our first LIGO data run § Our Plan » Improved data run is underway » Our goal is to obtain one year of integrated data at design sensitivity before the end of 2006 » Advanced interferometer with dramatically improved sensitivity – 2007+ § LIGO should be detecting gravitational waves within the next decade ! 10 -April-03 Penn State -- Colloquium 62