# Probing the Universe for Gravitational Waves LIGO Caltech

- Slides: 73

Probing the Universe for Gravitational Waves LIGO / Caltech LIGO Barry Barish Caltech 5 -June-03 LIGO-G 030284 -00 -M 5 -June-03 Caltech Colloquium

Gravitational Waves sources and detection Gravitational Wave Astrophysical Source Terrestrial detectors LIGO, TAMA, Virgo, AIGO Detectors in space LISA 5 -June-03 Caltech Colloquium 2

Detecting a passing wave …. Free masses 5 -June-03 Caltech Colloquium 3

Detecting a passing wave …. Interferometer 5 -June-03 Caltech Colloquium 4

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 5 -June-03 As a wave passes, the arm lengths change in different ways…. Caltech Colloquium 5

The Laboratory Sites Laser Interferometer Gravitational-wave Observatory (LIGO) Hanford Observatory Livingston Observatory 5 -June-03 Caltech Colloquium 6

LIGO: A View from the Bulldozers 5 -June-03 Caltech Colloquium 7

From Bulldozers to First Results 5 -June-03 Caltech Colloquium 8

Construction in Washington 5 -June-03 Caltech Colloquium 9

Flooding in Louisiana 5 -June-03 Caltech Colloquium 10

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

LIGO I the noise floor § Interferometry is limited by three fundamental noise sources Ø seismic noise at the lowest frequencies Ø thermal noise at intermediate frequencies Ø shot noise at high frequencies §Many other noise sources lurk underneath and must be controlled as the instrument is improved 5 -June-03 Caltech Colloquium 12

Dirt Moving to Mechanical arches and beam tubes Concrete Arches beamtube transport girth welding beamtube install 5 -June-03 Caltech Colloquium 13

LIGO beam tube § LIGO beam tube under constructi § 65 ft spiral welded sections § girth welded in portable clean roo 1. 2 m diameter - 3 mm stainless 50 km of weld 5 -June-03 Caltech Colloquium NO LEAKS !! 14

LIGO I the noise floor § Interferometry is limited by three fundamental noise sources Ø seismic noise at the lowest frequencies Ø thermal noise at intermediate frequencies Ø shot noise at high frequencies §Many other noise sources lurk underneath and must be controlled as the instrument is improved 5 -June-03 Caltech Colloquium 15

Beam Tube bakeou • I = 2000 amps for ~ 1 week • no leaks !! • final vacuum at level where not limiting noise, even for future detectors 5 -June-03 Caltech Colloquium 16

LIGO I the noise floor § Interferometry is limited by three fundamental noise sources Ø seismic noise at the lowest frequencies Ø thermal noise at intermediate frequencies Ø shot noise at high frequencies §Many other noise sources lurk underneath and must be controlled as the instrument is improved 5 -June-03 Caltech Colloquium 17

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 5 -June-03 Caltech Colloquium 18

Seismic Isolation springs and masses damped spring cross section 5 -June-03 Caltech Colloquium 19

Seismic Isolation performance HAM stack in air 102 100 10 -2 10 -6 10 -4 Horizontal 10 -6 BSC stack in vacuum 5 -June-03 Caltech Colloquium 10 -8 Vertical 10 -10 20

LIGO vacuum equipment 5 -June-03 Caltech Colloquium 21

LIGO Livingston Observatory 5 -June-03 Caltech Colloquium 22

Welcome to Louisiana pet alligator collecting bullet holes 5 -June-03 Caltech Colloquium 23

LIGO Hanford Observatory 5 -June-03 Caltech Colloquium 24

Gliches at Hanford a view from the bridge LIGO as a car stop desert on fire LIGO as a fire break 5 -June-03 Caltech Colloquium 25

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 5 -June-03 Caltech 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 5 -June-03 Caltech Colloquium 27

Core Optics installation and alignment 5 -June-03 Caltech Colloquium 28

LIGO Construction Complete 5 -June-03 Caltech Colloquium 29

LIGO Inauguration Whitcomb Caltech Boss 5 -June-03 Sanders The masses Caltech Colloquium Lazzarini NSF Boss 30

Locking the Interferometers 5 -June-03 Caltech Colloquium 31

LIGO “first lock” Composite Video Y Arm Laser X Arm signal 5 -June-03 Caltech Colloquium 32

Watching the Interferometer Lock Y arm X arm 2 min Y Arm Reflected light Anti-symmetric port Laser X Arm signal 5 -June-03 Caltech Colloquium 33

Lock Acquisition Matt Evans Caltech grad student 5 -June-03 Caltech Colloquium 34

Detecting Earthquakes From electronic logbook 2 -Jan-02 An earthquake occurred, starting at UTC 17: 38. 5 -June-03 Caltech Colloquium 35

Detecting the Earth Tides Sun and Moon Eric Morgenson Caltech Sophomore Summer ‘ 99 5 -June-03 Caltech Colloquium 36

Making LIGO Work 5 -June-03 Caltech Colloquium 37

Tidal Compensation Data Tidal evaluation on 21 -hour locked section of S 1 data Predicted tides Feedforward Feedback Residual signal on voice coils Residual signal on laser 5 -June-03 Caltech Colloquium 38

Controlling angular degrees of freedom 5 -June-03 Caltech Colloquium 39

LIGO Control Room 5 -June-03 Caltech Colloquium 40

LIGO 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 5 -June-03 Caltech Colloquium 41

Worldwide Network simultaneously detect signal LIGO GEO decompose the polarization of detection locate theconfidence sources gravitational waves 5 -June-03 Caltech Colloquium Virgo TAMA AIGO 42

Improving the Sensitivity • Seismic noise & vibration limit at low frequencies • Atomic vibrations (Thermal Noise) inside components limit at mid frequencies • Quantum nature of light (Shot Noise) limits at high frequencies • Myriad details of the lasers, electronics, etc. , can make problems above these levels 5 -June-03 Caltech Colloquium 43

LIGO Sensitivity Livingston 4 km Interferometer First Science Run 17 days - Sept 02 May 01 Jan 03 Second Science Run 59 days - April 03 5 -June-03 Caltech Colloquium 44

The First Science Run s 1 5 -June-03 Caltech Colloquium 45

Sensitivity during S 1 LIGO S 1 Run -----“First Upper Limit Run” § 23 Aug– 9 Sept 2002 § 17 days §All interferometers in power recycling configuration LHO 2 Km LHO 4 Km LLO 4 Km GEO in S 1 RUN -----Ran simultaneously In power recycling Lesser sensitivity 5 -June-03 Caltech Colloquium 46

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” 5 -June-03 Caltech Colloquium 47

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 5 -June-03 Caltech Colloquium 48

Compact binary collisions “chirps” » Neutron Star – waveforms are well described » Black Hole – need better waveforms » Search: matched templates 5 -June-03 Caltech Colloquium 49

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 5 -June-03 Caltech Colloquium 50

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 5 -June-03 Caltech Colloquium 51

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 5 -June-03 Caltech Colloquium 52

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 Detectable Range for S 2 data will reach Andromeda! 5 -June-03 Caltech Colloquium 53

Burst Sources signatures § 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). 5 -June-03 Caltech Colloquium 54

‘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 5 -June-03 Caltech Colloquium 55

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) 5 -June-03 10 Caltech Colloquium 56

Upper Limit 1 ms gaussian bursts Result is derived using ‘TFCLUSTERS’ algorithm Upper limit in strain compared to earlier (cryogenic bar) results: 90% confidence • 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 5 -June-03 Caltech Colloquium 57

Astrophysical Sources 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. An afterlife of stars 5 -June-03 Caltech Colloquium 58

Directed searches NO DETECTION EXPECTED at present sensitivities Crab Pulsar Limits of detectability for rotating NS with equatorial ellipticity e = d. I/Izz: 10 -3 , 10 -4 , 10 -5 @ 8. 5 kpc. PSR J 1939+2134 5 -June-03 Caltech Colloquium 1283. 86 Hz 59

Two Search Methods Frequency domain Time domain • Best suited for large parameter space searches • Maximum likelihood detection method + frequentist approach • 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 5 -June-03 Caltech Colloquium 60

The Data time behavior days 5 -June-03 Caltech Colloquium days 61

The Data frequency behavior 5 -June-03 Hz Hz Caltech Colloquium 62

PSR J 1939+2134 Frequency domain Injected signal in LLO: h = 2. 83 x 10 -22 • 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 5 -June-03 Caltech Colloquium 63

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 5 -June-03 95% h = 2. 1 x 10 -21 Caltech Colloquium 64

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 • Best previous results for PSR J 1939+2134: ho < 10 -20 (Glasgow, Hough et al. , 1983), 5 -June-03 Caltech Colloquium 65

Upper limit on pulsar ellipticity J 1939+2134 moment of inertia tensor gravitational ellipticity of pulsar h 0 < 1 10 -22 e < 7. 5 10 -5 R (M=1. 4 Msun, r=10 km, R=3. 6 kpc) • assuming emission due to deviation from axisymmetry: . . 5 -June-03 Caltech Colloquium 66

Early Universe stochastic background ‘Murmurs’ from the Big Bang Cosmic Microwave background WMAP 2003 5 -June-03 Caltech Colloquium 67

Stochastic Background § 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 5 -June-03 Hanford - Hanford Caltech Colloquium 68

Preliminary 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 cross-correlation; currently being investigated. § Previous best upper limits: » Measured: Garching-Glasgow interferometers : » Measured: EXPLORER-NAUTILUS (cryogenic bars): 5 -June-03 Caltech Colloquium 69

Stochastic Background sensitivities and theory E 7 results projected S 1 S 2 LIGO Adv LIGO 5 -June-03 Caltech Colloquium 70

Advanced LIGO improved subsystems Multiple Suspensions Active Seismic Sapphire Optics Higher Power Laser 5 -June-03 Caltech Colloquium 71

Advanced LIGO 2007 + • • Enhanced Systems laser suspension seismic isolation test mass Improvement factor in rate ~ 104 + narrow band optical configuration 5 -June-03 Caltech Colloquium 72

Probing the Universe with LIGO a glimpse at the science § 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 “in the can” from second data run – S 2 » 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 ! 5 -June-03 Caltech Colloquium 73

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